1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Peephole optimize the CFG.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Utils/Local.h"
15#include "llvm/ADT/DenseMap.h"
16#include "llvm/ADT/STLExtras.h"
17#include "llvm/ADT/SetOperations.h"
18#include "llvm/ADT/SetVector.h"
19#include "llvm/ADT/SmallPtrSet.h"
20#include "llvm/ADT/SmallVector.h"
21#include "llvm/ADT/Statistic.h"
22#include "llvm/Analysis/ConstantFolding.h"
23#include "llvm/Analysis/InstructionSimplify.h"
24#include "llvm/Analysis/TargetTransformInfo.h"
25#include "llvm/Analysis/ValueTracking.h"
26#include "llvm/IR/CFG.h"
27#include "llvm/IR/ConstantRange.h"
28#include "llvm/IR/Constants.h"
29#include "llvm/IR/DataLayout.h"
30#include "llvm/IR/DerivedTypes.h"
31#include "llvm/IR/GlobalVariable.h"
32#include "llvm/IR/IRBuilder.h"
33#include "llvm/IR/Instructions.h"
34#include "llvm/IR/IntrinsicInst.h"
35#include "llvm/IR/LLVMContext.h"
36#include "llvm/IR/MDBuilder.h"
37#include "llvm/IR/Metadata.h"
38#include "llvm/IR/Module.h"
39#include "llvm/IR/NoFolder.h"
40#include "llvm/IR/Operator.h"
41#include "llvm/IR/PatternMatch.h"
42#include "llvm/IR/Type.h"
43#include "llvm/Support/CommandLine.h"
44#include "llvm/Support/Debug.h"
45#include "llvm/Support/raw_ostream.h"
46#include "llvm/Transforms/Utils/BasicBlockUtils.h"
47#include "llvm/Transforms/Utils/ValueMapper.h"
48#include <algorithm>
49#include <map>
50#include <set>
51using namespace llvm;
52using namespace PatternMatch;
53
54#define DEBUG_TYPE "simplifycfg"
55
56// Chosen as 2 so as to be cheap, but still to have enough power to fold
57// a select, so the "clamp" idiom (of a min followed by a max) will be caught.
58// To catch this, we need to fold a compare and a select, hence '2' being the
59// minimum reasonable default.
60static cl::opt<unsigned>
61PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(2),
62   cl::desc("Control the amount of phi node folding to perform (default = 2)"));
63
64static cl::opt<bool>
65DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
66       cl::desc("Duplicate return instructions into unconditional branches"));
67
68static cl::opt<bool>
69SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
70       cl::desc("Sink common instructions down to the end block"));
71
72static cl::opt<bool> HoistCondStores(
73    "simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
74    cl::desc("Hoist conditional stores if an unconditional store precedes"));
75
76static cl::opt<bool> MergeCondStores(
77    "simplifycfg-merge-cond-stores", cl::Hidden, cl::init(true),
78    cl::desc("Hoist conditional stores even if an unconditional store does not "
79             "precede - hoist multiple conditional stores into a single "
80             "predicated store"));
81
82static cl::opt<bool> MergeCondStoresAggressively(
83    "simplifycfg-merge-cond-stores-aggressively", cl::Hidden, cl::init(false),
84    cl::desc("When merging conditional stores, do so even if the resultant "
85             "basic blocks are unlikely to be if-converted as a result"));
86
87static cl::opt<bool> SpeculateOneExpensiveInst(
88    "speculate-one-expensive-inst", cl::Hidden, cl::init(true),
89    cl::desc("Allow exactly one expensive instruction to be speculatively "
90             "executed"));
91
92STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
93STATISTIC(NumLinearMaps, "Number of switch instructions turned into linear mapping");
94STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
95STATISTIC(NumLookupTablesHoles, "Number of switch instructions turned into lookup tables (holes checked)");
96STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares");
97STATISTIC(NumSinkCommons, "Number of common instructions sunk down to the end block");
98STATISTIC(NumSpeculations, "Number of speculative executed instructions");
99
100namespace {
101  // The first field contains the value that the switch produces when a certain
102  // case group is selected, and the second field is a vector containing the
103  // cases composing the case group.
104  typedef SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>
105    SwitchCaseResultVectorTy;
106  // The first field contains the phi node that generates a result of the switch
107  // and the second field contains the value generated for a certain case in the
108  // switch for that PHI.
109  typedef SmallVector<std::pair<PHINode *, Constant *>, 4> SwitchCaseResultsTy;
110
111  /// ValueEqualityComparisonCase - Represents a case of a switch.
112  struct ValueEqualityComparisonCase {
113    ConstantInt *Value;
114    BasicBlock *Dest;
115
116    ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
117      : Value(Value), Dest(Dest) {}
118
119    bool operator<(ValueEqualityComparisonCase RHS) const {
120      // Comparing pointers is ok as we only rely on the order for uniquing.
121      return Value < RHS.Value;
122    }
123
124    bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
125  };
126
127class SimplifyCFGOpt {
128  const TargetTransformInfo &TTI;
129  const DataLayout &DL;
130  unsigned BonusInstThreshold;
131  AssumptionCache *AC;
132  Value *isValueEqualityComparison(TerminatorInst *TI);
133  BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
134                               std::vector<ValueEqualityComparisonCase> &Cases);
135  bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
136                                                     BasicBlock *Pred,
137                                                     IRBuilder<> &Builder);
138  bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
139                                           IRBuilder<> &Builder);
140
141  bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
142  bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
143  bool SimplifyCleanupReturn(CleanupReturnInst *RI);
144  bool SimplifyUnreachable(UnreachableInst *UI);
145  bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
146  bool SimplifyIndirectBr(IndirectBrInst *IBI);
147  bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
148  bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
149
150public:
151  SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL,
152                 unsigned BonusInstThreshold, AssumptionCache *AC)
153      : TTI(TTI), DL(DL), BonusInstThreshold(BonusInstThreshold), AC(AC) {}
154  bool run(BasicBlock *BB);
155};
156}
157
158/// Return true if it is safe to merge these two
159/// terminator instructions together.
160static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
161  if (SI1 == SI2) return false;  // Can't merge with self!
162
163  // It is not safe to merge these two switch instructions if they have a common
164  // successor, and if that successor has a PHI node, and if *that* PHI node has
165  // conflicting incoming values from the two switch blocks.
166  BasicBlock *SI1BB = SI1->getParent();
167  BasicBlock *SI2BB = SI2->getParent();
168  SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
169
170  for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
171    if (SI1Succs.count(*I))
172      for (BasicBlock::iterator BBI = (*I)->begin();
173           isa<PHINode>(BBI); ++BBI) {
174        PHINode *PN = cast<PHINode>(BBI);
175        if (PN->getIncomingValueForBlock(SI1BB) !=
176            PN->getIncomingValueForBlock(SI2BB))
177          return false;
178      }
179
180  return true;
181}
182
183/// Return true if it is safe and profitable to merge these two terminator
184/// instructions together, where SI1 is an unconditional branch. PhiNodes will
185/// store all PHI nodes in common successors.
186static bool isProfitableToFoldUnconditional(BranchInst *SI1,
187                                          BranchInst *SI2,
188                                          Instruction *Cond,
189                                          SmallVectorImpl<PHINode*> &PhiNodes) {
190  if (SI1 == SI2) return false;  // Can't merge with self!
191  assert(SI1->isUnconditional() && SI2->isConditional());
192
193  // We fold the unconditional branch if we can easily update all PHI nodes in
194  // common successors:
195  // 1> We have a constant incoming value for the conditional branch;
196  // 2> We have "Cond" as the incoming value for the unconditional branch;
197  // 3> SI2->getCondition() and Cond have same operands.
198  CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
199  if (!Ci2) return false;
200  if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
201        Cond->getOperand(1) == Ci2->getOperand(1)) &&
202      !(Cond->getOperand(0) == Ci2->getOperand(1) &&
203        Cond->getOperand(1) == Ci2->getOperand(0)))
204    return false;
205
206  BasicBlock *SI1BB = SI1->getParent();
207  BasicBlock *SI2BB = SI2->getParent();
208  SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
209  for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
210    if (SI1Succs.count(*I))
211      for (BasicBlock::iterator BBI = (*I)->begin();
212           isa<PHINode>(BBI); ++BBI) {
213        PHINode *PN = cast<PHINode>(BBI);
214        if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
215            !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
216          return false;
217        PhiNodes.push_back(PN);
218      }
219  return true;
220}
221
222/// Update PHI nodes in Succ to indicate that there will now be entries in it
223/// from the 'NewPred' block. The values that will be flowing into the PHI nodes
224/// will be the same as those coming in from ExistPred, an existing predecessor
225/// of Succ.
226static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
227                                  BasicBlock *ExistPred) {
228  if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
229
230  PHINode *PN;
231  for (BasicBlock::iterator I = Succ->begin();
232       (PN = dyn_cast<PHINode>(I)); ++I)
233    PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
234}
235
236/// Compute an abstract "cost" of speculating the given instruction,
237/// which is assumed to be safe to speculate. TCC_Free means cheap,
238/// TCC_Basic means less cheap, and TCC_Expensive means prohibitively
239/// expensive.
240static unsigned ComputeSpeculationCost(const User *I,
241                                       const TargetTransformInfo &TTI) {
242  assert(isSafeToSpeculativelyExecute(I) &&
243         "Instruction is not safe to speculatively execute!");
244  return TTI.getUserCost(I);
245}
246
247/// If we have a merge point of an "if condition" as accepted above,
248/// return true if the specified value dominates the block.  We
249/// don't handle the true generality of domination here, just a special case
250/// which works well enough for us.
251///
252/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
253/// see if V (which must be an instruction) and its recursive operands
254/// that do not dominate BB have a combined cost lower than CostRemaining and
255/// are non-trapping.  If both are true, the instruction is inserted into the
256/// set and true is returned.
257///
258/// The cost for most non-trapping instructions is defined as 1 except for
259/// Select whose cost is 2.
260///
261/// After this function returns, CostRemaining is decreased by the cost of
262/// V plus its non-dominating operands.  If that cost is greater than
263/// CostRemaining, false is returned and CostRemaining is undefined.
264static bool DominatesMergePoint(Value *V, BasicBlock *BB,
265                                SmallPtrSetImpl<Instruction*> *AggressiveInsts,
266                                unsigned &CostRemaining,
267                                const TargetTransformInfo &TTI,
268                                unsigned Depth = 0) {
269  Instruction *I = dyn_cast<Instruction>(V);
270  if (!I) {
271    // Non-instructions all dominate instructions, but not all constantexprs
272    // can be executed unconditionally.
273    if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
274      if (C->canTrap())
275        return false;
276    return true;
277  }
278  BasicBlock *PBB = I->getParent();
279
280  // We don't want to allow weird loops that might have the "if condition" in
281  // the bottom of this block.
282  if (PBB == BB) return false;
283
284  // If this instruction is defined in a block that contains an unconditional
285  // branch to BB, then it must be in the 'conditional' part of the "if
286  // statement".  If not, it definitely dominates the region.
287  BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
288  if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB)
289    return true;
290
291  // If we aren't allowing aggressive promotion anymore, then don't consider
292  // instructions in the 'if region'.
293  if (!AggressiveInsts) return false;
294
295  // If we have seen this instruction before, don't count it again.
296  if (AggressiveInsts->count(I)) return true;
297
298  // Okay, it looks like the instruction IS in the "condition".  Check to
299  // see if it's a cheap instruction to unconditionally compute, and if it
300  // only uses stuff defined outside of the condition.  If so, hoist it out.
301  if (!isSafeToSpeculativelyExecute(I))
302    return false;
303
304  unsigned Cost = ComputeSpeculationCost(I, TTI);
305
306  // Allow exactly one instruction to be speculated regardless of its cost
307  // (as long as it is safe to do so).
308  // This is intended to flatten the CFG even if the instruction is a division
309  // or other expensive operation. The speculation of an expensive instruction
310  // is expected to be undone in CodeGenPrepare if the speculation has not
311  // enabled further IR optimizations.
312  if (Cost > CostRemaining &&
313      (!SpeculateOneExpensiveInst || !AggressiveInsts->empty() || Depth > 0))
314    return false;
315
316  // Avoid unsigned wrap.
317  CostRemaining = (Cost > CostRemaining) ? 0 : CostRemaining - Cost;
318
319  // Okay, we can only really hoist these out if their operands do
320  // not take us over the cost threshold.
321  for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
322    if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI,
323                             Depth + 1))
324      return false;
325  // Okay, it's safe to do this!  Remember this instruction.
326  AggressiveInsts->insert(I);
327  return true;
328}
329
330/// Extract ConstantInt from value, looking through IntToPtr
331/// and PointerNullValue. Return NULL if value is not a constant int.
332static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
333  // Normal constant int.
334  ConstantInt *CI = dyn_cast<ConstantInt>(V);
335  if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy())
336    return CI;
337
338  // This is some kind of pointer constant. Turn it into a pointer-sized
339  // ConstantInt if possible.
340  IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
341
342  // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
343  if (isa<ConstantPointerNull>(V))
344    return ConstantInt::get(PtrTy, 0);
345
346  // IntToPtr const int.
347  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
348    if (CE->getOpcode() == Instruction::IntToPtr)
349      if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
350        // The constant is very likely to have the right type already.
351        if (CI->getType() == PtrTy)
352          return CI;
353        else
354          return cast<ConstantInt>
355            (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
356      }
357  return nullptr;
358}
359
360namespace {
361
362/// Given a chain of or (||) or and (&&) comparison of a value against a
363/// constant, this will try to recover the information required for a switch
364/// structure.
365/// It will depth-first traverse the chain of comparison, seeking for patterns
366/// like %a == 12 or %a < 4 and combine them to produce a set of integer
367/// representing the different cases for the switch.
368/// Note that if the chain is composed of '||' it will build the set of elements
369/// that matches the comparisons (i.e. any of this value validate the chain)
370/// while for a chain of '&&' it will build the set elements that make the test
371/// fail.
372struct ConstantComparesGatherer {
373  const DataLayout &DL;
374  Value *CompValue; /// Value found for the switch comparison
375  Value *Extra;     /// Extra clause to be checked before the switch
376  SmallVector<ConstantInt *, 8> Vals; /// Set of integers to match in switch
377  unsigned UsedICmps; /// Number of comparisons matched in the and/or chain
378
379  /// Construct and compute the result for the comparison instruction Cond
380  ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL)
381      : DL(DL), CompValue(nullptr), Extra(nullptr), UsedICmps(0) {
382    gather(Cond);
383  }
384
385  /// Prevent copy
386  ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
387  ConstantComparesGatherer &
388  operator=(const ConstantComparesGatherer &) = delete;
389
390private:
391
392  /// Try to set the current value used for the comparison, it succeeds only if
393  /// it wasn't set before or if the new value is the same as the old one
394  bool setValueOnce(Value *NewVal) {
395    if(CompValue && CompValue != NewVal) return false;
396    CompValue = NewVal;
397    return (CompValue != nullptr);
398  }
399
400  /// Try to match Instruction "I" as a comparison against a constant and
401  /// populates the array Vals with the set of values that match (or do not
402  /// match depending on isEQ).
403  /// Return false on failure. On success, the Value the comparison matched
404  /// against is placed in CompValue.
405  /// If CompValue is already set, the function is expected to fail if a match
406  /// is found but the value compared to is different.
407  bool matchInstruction(Instruction *I, bool isEQ) {
408    // If this is an icmp against a constant, handle this as one of the cases.
409    ICmpInst *ICI;
410    ConstantInt *C;
411    if (!((ICI = dyn_cast<ICmpInst>(I)) &&
412             (C = GetConstantInt(I->getOperand(1), DL)))) {
413      return false;
414    }
415
416    Value *RHSVal;
417    ConstantInt *RHSC;
418
419    // Pattern match a special case
420    // (x & ~2^x) == y --> x == y || x == y|2^x
421    // This undoes a transformation done by instcombine to fuse 2 compares.
422    if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
423      if (match(ICI->getOperand(0),
424                m_And(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
425        APInt Not = ~RHSC->getValue();
426        if (Not.isPowerOf2()) {
427          // If we already have a value for the switch, it has to match!
428          if(!setValueOnce(RHSVal))
429            return false;
430
431          Vals.push_back(C);
432          Vals.push_back(ConstantInt::get(C->getContext(),
433                                          C->getValue() | Not));
434          UsedICmps++;
435          return true;
436        }
437      }
438
439      // If we already have a value for the switch, it has to match!
440      if(!setValueOnce(ICI->getOperand(0)))
441        return false;
442
443      UsedICmps++;
444      Vals.push_back(C);
445      return ICI->getOperand(0);
446    }
447
448    // If we have "x ult 3", for example, then we can add 0,1,2 to the set.
449    ConstantRange Span = ConstantRange::makeAllowedICmpRegion(
450        ICI->getPredicate(), C->getValue());
451
452    // Shift the range if the compare is fed by an add. This is the range
453    // compare idiom as emitted by instcombine.
454    Value *CandidateVal = I->getOperand(0);
455    if(match(I->getOperand(0), m_Add(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
456      Span = Span.subtract(RHSC->getValue());
457      CandidateVal = RHSVal;
458    }
459
460    // If this is an and/!= check, then we are looking to build the set of
461    // value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
462    // x != 0 && x != 1.
463    if (!isEQ)
464      Span = Span.inverse();
465
466    // If there are a ton of values, we don't want to make a ginormous switch.
467    if (Span.getSetSize().ugt(8) || Span.isEmptySet()) {
468      return false;
469    }
470
471    // If we already have a value for the switch, it has to match!
472    if(!setValueOnce(CandidateVal))
473      return false;
474
475    // Add all values from the range to the set
476    for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
477      Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
478
479    UsedICmps++;
480    return true;
481
482  }
483
484  /// Given a potentially 'or'd or 'and'd together collection of icmp
485  /// eq/ne/lt/gt instructions that compare a value against a constant, extract
486  /// the value being compared, and stick the list constants into the Vals
487  /// vector.
488  /// One "Extra" case is allowed to differ from the other.
489  void gather(Value *V) {
490    Instruction *I = dyn_cast<Instruction>(V);
491    bool isEQ = (I->getOpcode() == Instruction::Or);
492
493    // Keep a stack (SmallVector for efficiency) for depth-first traversal
494    SmallVector<Value *, 8> DFT;
495
496    // Initialize
497    DFT.push_back(V);
498
499    while(!DFT.empty()) {
500      V = DFT.pop_back_val();
501
502      if (Instruction *I = dyn_cast<Instruction>(V)) {
503        // If it is a || (or && depending on isEQ), process the operands.
504        if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
505          DFT.push_back(I->getOperand(1));
506          DFT.push_back(I->getOperand(0));
507          continue;
508        }
509
510        // Try to match the current instruction
511        if (matchInstruction(I, isEQ))
512          // Match succeed, continue the loop
513          continue;
514      }
515
516      // One element of the sequence of || (or &&) could not be match as a
517      // comparison against the same value as the others.
518      // We allow only one "Extra" case to be checked before the switch
519      if (!Extra) {
520        Extra = V;
521        continue;
522      }
523      // Failed to parse a proper sequence, abort now
524      CompValue = nullptr;
525      break;
526    }
527  }
528};
529
530}
531
532static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
533  Instruction *Cond = nullptr;
534  if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
535    Cond = dyn_cast<Instruction>(SI->getCondition());
536  } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
537    if (BI->isConditional())
538      Cond = dyn_cast<Instruction>(BI->getCondition());
539  } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
540    Cond = dyn_cast<Instruction>(IBI->getAddress());
541  }
542
543  TI->eraseFromParent();
544  if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
545}
546
547/// Return true if the specified terminator checks
548/// to see if a value is equal to constant integer value.
549Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
550  Value *CV = nullptr;
551  if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
552    // Do not permit merging of large switch instructions into their
553    // predecessors unless there is only one predecessor.
554    if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
555                                             pred_end(SI->getParent())) <= 128)
556      CV = SI->getCondition();
557  } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
558    if (BI->isConditional() && BI->getCondition()->hasOneUse())
559      if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
560        if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL))
561          CV = ICI->getOperand(0);
562      }
563
564  // Unwrap any lossless ptrtoint cast.
565  if (CV) {
566    if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) {
567      Value *Ptr = PTII->getPointerOperand();
568      if (PTII->getType() == DL.getIntPtrType(Ptr->getType()))
569        CV = Ptr;
570    }
571  }
572  return CV;
573}
574
575/// Given a value comparison instruction,
576/// decode all of the 'cases' that it represents and return the 'default' block.
577BasicBlock *SimplifyCFGOpt::
578GetValueEqualityComparisonCases(TerminatorInst *TI,
579                                std::vector<ValueEqualityComparisonCase>
580                                                                       &Cases) {
581  if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
582    Cases.reserve(SI->getNumCases());
583    for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
584      Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
585                                                  i.getCaseSuccessor()));
586    return SI->getDefaultDest();
587  }
588
589  BranchInst *BI = cast<BranchInst>(TI);
590  ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
591  BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
592  Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
593                                                             DL),
594                                              Succ));
595  return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
596}
597
598
599/// Given a vector of bb/value pairs, remove any entries
600/// in the list that match the specified block.
601static void EliminateBlockCases(BasicBlock *BB,
602                              std::vector<ValueEqualityComparisonCase> &Cases) {
603  Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
604}
605
606/// Return true if there are any keys in C1 that exist in C2 as well.
607static bool
608ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
609              std::vector<ValueEqualityComparisonCase > &C2) {
610  std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
611
612  // Make V1 be smaller than V2.
613  if (V1->size() > V2->size())
614    std::swap(V1, V2);
615
616  if (V1->size() == 0) return false;
617  if (V1->size() == 1) {
618    // Just scan V2.
619    ConstantInt *TheVal = (*V1)[0].Value;
620    for (unsigned i = 0, e = V2->size(); i != e; ++i)
621      if (TheVal == (*V2)[i].Value)
622        return true;
623  }
624
625  // Otherwise, just sort both lists and compare element by element.
626  array_pod_sort(V1->begin(), V1->end());
627  array_pod_sort(V2->begin(), V2->end());
628  unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
629  while (i1 != e1 && i2 != e2) {
630    if ((*V1)[i1].Value == (*V2)[i2].Value)
631      return true;
632    if ((*V1)[i1].Value < (*V2)[i2].Value)
633      ++i1;
634    else
635      ++i2;
636  }
637  return false;
638}
639
640/// If TI is known to be a terminator instruction and its block is known to
641/// only have a single predecessor block, check to see if that predecessor is
642/// also a value comparison with the same value, and if that comparison
643/// determines the outcome of this comparison. If so, simplify TI. This does a
644/// very limited form of jump threading.
645bool SimplifyCFGOpt::
646SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
647                                              BasicBlock *Pred,
648                                              IRBuilder<> &Builder) {
649  Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
650  if (!PredVal) return false;  // Not a value comparison in predecessor.
651
652  Value *ThisVal = isValueEqualityComparison(TI);
653  assert(ThisVal && "This isn't a value comparison!!");
654  if (ThisVal != PredVal) return false;  // Different predicates.
655
656  // TODO: Preserve branch weight metadata, similarly to how
657  // FoldValueComparisonIntoPredecessors preserves it.
658
659  // Find out information about when control will move from Pred to TI's block.
660  std::vector<ValueEqualityComparisonCase> PredCases;
661  BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
662                                                        PredCases);
663  EliminateBlockCases(PredDef, PredCases);  // Remove default from cases.
664
665  // Find information about how control leaves this block.
666  std::vector<ValueEqualityComparisonCase> ThisCases;
667  BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
668  EliminateBlockCases(ThisDef, ThisCases);  // Remove default from cases.
669
670  // If TI's block is the default block from Pred's comparison, potentially
671  // simplify TI based on this knowledge.
672  if (PredDef == TI->getParent()) {
673    // If we are here, we know that the value is none of those cases listed in
674    // PredCases.  If there are any cases in ThisCases that are in PredCases, we
675    // can simplify TI.
676    if (!ValuesOverlap(PredCases, ThisCases))
677      return false;
678
679    if (isa<BranchInst>(TI)) {
680      // Okay, one of the successors of this condbr is dead.  Convert it to a
681      // uncond br.
682      assert(ThisCases.size() == 1 && "Branch can only have one case!");
683      // Insert the new branch.
684      Instruction *NI = Builder.CreateBr(ThisDef);
685      (void) NI;
686
687      // Remove PHI node entries for the dead edge.
688      ThisCases[0].Dest->removePredecessor(TI->getParent());
689
690      DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
691           << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
692
693      EraseTerminatorInstAndDCECond(TI);
694      return true;
695    }
696
697    SwitchInst *SI = cast<SwitchInst>(TI);
698    // Okay, TI has cases that are statically dead, prune them away.
699    SmallPtrSet<Constant*, 16> DeadCases;
700    for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
701      DeadCases.insert(PredCases[i].Value);
702
703    DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
704                 << "Through successor TI: " << *TI);
705
706    // Collect branch weights into a vector.
707    SmallVector<uint32_t, 8> Weights;
708    MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
709    bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
710    if (HasWeight)
711      for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
712           ++MD_i) {
713        ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
714        Weights.push_back(CI->getValue().getZExtValue());
715      }
716    for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
717      --i;
718      if (DeadCases.count(i.getCaseValue())) {
719        if (HasWeight) {
720          std::swap(Weights[i.getCaseIndex()+1], Weights.back());
721          Weights.pop_back();
722        }
723        i.getCaseSuccessor()->removePredecessor(TI->getParent());
724        SI->removeCase(i);
725      }
726    }
727    if (HasWeight && Weights.size() >= 2)
728      SI->setMetadata(LLVMContext::MD_prof,
729                      MDBuilder(SI->getParent()->getContext()).
730                      createBranchWeights(Weights));
731
732    DEBUG(dbgs() << "Leaving: " << *TI << "\n");
733    return true;
734  }
735
736  // Otherwise, TI's block must correspond to some matched value.  Find out
737  // which value (or set of values) this is.
738  ConstantInt *TIV = nullptr;
739  BasicBlock *TIBB = TI->getParent();
740  for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
741    if (PredCases[i].Dest == TIBB) {
742      if (TIV)
743        return false;  // Cannot handle multiple values coming to this block.
744      TIV = PredCases[i].Value;
745    }
746  assert(TIV && "No edge from pred to succ?");
747
748  // Okay, we found the one constant that our value can be if we get into TI's
749  // BB.  Find out which successor will unconditionally be branched to.
750  BasicBlock *TheRealDest = nullptr;
751  for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
752    if (ThisCases[i].Value == TIV) {
753      TheRealDest = ThisCases[i].Dest;
754      break;
755    }
756
757  // If not handled by any explicit cases, it is handled by the default case.
758  if (!TheRealDest) TheRealDest = ThisDef;
759
760  // Remove PHI node entries for dead edges.
761  BasicBlock *CheckEdge = TheRealDest;
762  for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
763    if (*SI != CheckEdge)
764      (*SI)->removePredecessor(TIBB);
765    else
766      CheckEdge = nullptr;
767
768  // Insert the new branch.
769  Instruction *NI = Builder.CreateBr(TheRealDest);
770  (void) NI;
771
772  DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
773            << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
774
775  EraseTerminatorInstAndDCECond(TI);
776  return true;
777}
778
779namespace {
780  /// This class implements a stable ordering of constant
781  /// integers that does not depend on their address.  This is important for
782  /// applications that sort ConstantInt's to ensure uniqueness.
783  struct ConstantIntOrdering {
784    bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
785      return LHS->getValue().ult(RHS->getValue());
786    }
787  };
788}
789
790static int ConstantIntSortPredicate(ConstantInt *const *P1,
791                                    ConstantInt *const *P2) {
792  const ConstantInt *LHS = *P1;
793  const ConstantInt *RHS = *P2;
794  if (LHS->getValue().ult(RHS->getValue()))
795    return 1;
796  if (LHS->getValue() == RHS->getValue())
797    return 0;
798  return -1;
799}
800
801static inline bool HasBranchWeights(const Instruction* I) {
802  MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof);
803  if (ProfMD && ProfMD->getOperand(0))
804    if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
805      return MDS->getString().equals("branch_weights");
806
807  return false;
808}
809
810/// Get Weights of a given TerminatorInst, the default weight is at the front
811/// of the vector. If TI is a conditional eq, we need to swap the branch-weight
812/// metadata.
813static void GetBranchWeights(TerminatorInst *TI,
814                             SmallVectorImpl<uint64_t> &Weights) {
815  MDNode *MD = TI->getMetadata(LLVMContext::MD_prof);
816  assert(MD);
817  for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
818    ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i));
819    Weights.push_back(CI->getValue().getZExtValue());
820  }
821
822  // If TI is a conditional eq, the default case is the false case,
823  // and the corresponding branch-weight data is at index 2. We swap the
824  // default weight to be the first entry.
825  if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
826    assert(Weights.size() == 2);
827    ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
828    if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
829      std::swap(Weights.front(), Weights.back());
830  }
831}
832
833/// Keep halving the weights until all can fit in uint32_t.
834static void FitWeights(MutableArrayRef<uint64_t> Weights) {
835  uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
836  if (Max > UINT_MAX) {
837    unsigned Offset = 32 - countLeadingZeros(Max);
838    for (uint64_t &I : Weights)
839      I >>= Offset;
840  }
841}
842
843/// The specified terminator is a value equality comparison instruction
844/// (either a switch or a branch on "X == c").
845/// See if any of the predecessors of the terminator block are value comparisons
846/// on the same value.  If so, and if safe to do so, fold them together.
847bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
848                                                         IRBuilder<> &Builder) {
849  BasicBlock *BB = TI->getParent();
850  Value *CV = isValueEqualityComparison(TI);  // CondVal
851  assert(CV && "Not a comparison?");
852  bool Changed = false;
853
854  SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
855  while (!Preds.empty()) {
856    BasicBlock *Pred = Preds.pop_back_val();
857
858    // See if the predecessor is a comparison with the same value.
859    TerminatorInst *PTI = Pred->getTerminator();
860    Value *PCV = isValueEqualityComparison(PTI);  // PredCondVal
861
862    if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
863      // Figure out which 'cases' to copy from SI to PSI.
864      std::vector<ValueEqualityComparisonCase> BBCases;
865      BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
866
867      std::vector<ValueEqualityComparisonCase> PredCases;
868      BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
869
870      // Based on whether the default edge from PTI goes to BB or not, fill in
871      // PredCases and PredDefault with the new switch cases we would like to
872      // build.
873      SmallVector<BasicBlock*, 8> NewSuccessors;
874
875      // Update the branch weight metadata along the way
876      SmallVector<uint64_t, 8> Weights;
877      bool PredHasWeights = HasBranchWeights(PTI);
878      bool SuccHasWeights = HasBranchWeights(TI);
879
880      if (PredHasWeights) {
881        GetBranchWeights(PTI, Weights);
882        // branch-weight metadata is inconsistent here.
883        if (Weights.size() != 1 + PredCases.size())
884          PredHasWeights = SuccHasWeights = false;
885      } else if (SuccHasWeights)
886        // If there are no predecessor weights but there are successor weights,
887        // populate Weights with 1, which will later be scaled to the sum of
888        // successor's weights
889        Weights.assign(1 + PredCases.size(), 1);
890
891      SmallVector<uint64_t, 8> SuccWeights;
892      if (SuccHasWeights) {
893        GetBranchWeights(TI, SuccWeights);
894        // branch-weight metadata is inconsistent here.
895        if (SuccWeights.size() != 1 + BBCases.size())
896          PredHasWeights = SuccHasWeights = false;
897      } else if (PredHasWeights)
898        SuccWeights.assign(1 + BBCases.size(), 1);
899
900      if (PredDefault == BB) {
901        // If this is the default destination from PTI, only the edges in TI
902        // that don't occur in PTI, or that branch to BB will be activated.
903        std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
904        for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
905          if (PredCases[i].Dest != BB)
906            PTIHandled.insert(PredCases[i].Value);
907          else {
908            // The default destination is BB, we don't need explicit targets.
909            std::swap(PredCases[i], PredCases.back());
910
911            if (PredHasWeights || SuccHasWeights) {
912              // Increase weight for the default case.
913              Weights[0] += Weights[i+1];
914              std::swap(Weights[i+1], Weights.back());
915              Weights.pop_back();
916            }
917
918            PredCases.pop_back();
919            --i; --e;
920          }
921
922        // Reconstruct the new switch statement we will be building.
923        if (PredDefault != BBDefault) {
924          PredDefault->removePredecessor(Pred);
925          PredDefault = BBDefault;
926          NewSuccessors.push_back(BBDefault);
927        }
928
929        unsigned CasesFromPred = Weights.size();
930        uint64_t ValidTotalSuccWeight = 0;
931        for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
932          if (!PTIHandled.count(BBCases[i].Value) &&
933              BBCases[i].Dest != BBDefault) {
934            PredCases.push_back(BBCases[i]);
935            NewSuccessors.push_back(BBCases[i].Dest);
936            if (SuccHasWeights || PredHasWeights) {
937              // The default weight is at index 0, so weight for the ith case
938              // should be at index i+1. Scale the cases from successor by
939              // PredDefaultWeight (Weights[0]).
940              Weights.push_back(Weights[0] * SuccWeights[i+1]);
941              ValidTotalSuccWeight += SuccWeights[i+1];
942            }
943          }
944
945        if (SuccHasWeights || PredHasWeights) {
946          ValidTotalSuccWeight += SuccWeights[0];
947          // Scale the cases from predecessor by ValidTotalSuccWeight.
948          for (unsigned i = 1; i < CasesFromPred; ++i)
949            Weights[i] *= ValidTotalSuccWeight;
950          // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
951          Weights[0] *= SuccWeights[0];
952        }
953      } else {
954        // If this is not the default destination from PSI, only the edges
955        // in SI that occur in PSI with a destination of BB will be
956        // activated.
957        std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
958        std::map<ConstantInt*, uint64_t> WeightsForHandled;
959        for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
960          if (PredCases[i].Dest == BB) {
961            PTIHandled.insert(PredCases[i].Value);
962
963            if (PredHasWeights || SuccHasWeights) {
964              WeightsForHandled[PredCases[i].Value] = Weights[i+1];
965              std::swap(Weights[i+1], Weights.back());
966              Weights.pop_back();
967            }
968
969            std::swap(PredCases[i], PredCases.back());
970            PredCases.pop_back();
971            --i; --e;
972          }
973
974        // Okay, now we know which constants were sent to BB from the
975        // predecessor.  Figure out where they will all go now.
976        for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
977          if (PTIHandled.count(BBCases[i].Value)) {
978            // If this is one we are capable of getting...
979            if (PredHasWeights || SuccHasWeights)
980              Weights.push_back(WeightsForHandled[BBCases[i].Value]);
981            PredCases.push_back(BBCases[i]);
982            NewSuccessors.push_back(BBCases[i].Dest);
983            PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
984          }
985
986        // If there are any constants vectored to BB that TI doesn't handle,
987        // they must go to the default destination of TI.
988        for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
989                                    PTIHandled.begin(),
990               E = PTIHandled.end(); I != E; ++I) {
991          if (PredHasWeights || SuccHasWeights)
992            Weights.push_back(WeightsForHandled[*I]);
993          PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
994          NewSuccessors.push_back(BBDefault);
995        }
996      }
997
998      // Okay, at this point, we know which new successor Pred will get.  Make
999      // sure we update the number of entries in the PHI nodes for these
1000      // successors.
1001      for (BasicBlock *NewSuccessor : NewSuccessors)
1002        AddPredecessorToBlock(NewSuccessor, Pred, BB);
1003
1004      Builder.SetInsertPoint(PTI);
1005      // Convert pointer to int before we switch.
1006      if (CV->getType()->isPointerTy()) {
1007        CV = Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()),
1008                                    "magicptr");
1009      }
1010
1011      // Now that the successors are updated, create the new Switch instruction.
1012      SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
1013                                               PredCases.size());
1014      NewSI->setDebugLoc(PTI->getDebugLoc());
1015      for (ValueEqualityComparisonCase &V : PredCases)
1016        NewSI->addCase(V.Value, V.Dest);
1017
1018      if (PredHasWeights || SuccHasWeights) {
1019        // Halve the weights if any of them cannot fit in an uint32_t
1020        FitWeights(Weights);
1021
1022        SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1023
1024        NewSI->setMetadata(LLVMContext::MD_prof,
1025                           MDBuilder(BB->getContext()).
1026                           createBranchWeights(MDWeights));
1027      }
1028
1029      EraseTerminatorInstAndDCECond(PTI);
1030
1031      // Okay, last check.  If BB is still a successor of PSI, then we must
1032      // have an infinite loop case.  If so, add an infinitely looping block
1033      // to handle the case to preserve the behavior of the code.
1034      BasicBlock *InfLoopBlock = nullptr;
1035      for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1036        if (NewSI->getSuccessor(i) == BB) {
1037          if (!InfLoopBlock) {
1038            // Insert it at the end of the function, because it's either code,
1039            // or it won't matter if it's hot. :)
1040            InfLoopBlock = BasicBlock::Create(BB->getContext(),
1041                                              "infloop", BB->getParent());
1042            BranchInst::Create(InfLoopBlock, InfLoopBlock);
1043          }
1044          NewSI->setSuccessor(i, InfLoopBlock);
1045        }
1046
1047      Changed = true;
1048    }
1049  }
1050  return Changed;
1051}
1052
1053// If we would need to insert a select that uses the value of this invoke
1054// (comments in HoistThenElseCodeToIf explain why we would need to do this), we
1055// can't hoist the invoke, as there is nowhere to put the select in this case.
1056static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1057                                Instruction *I1, Instruction *I2) {
1058  for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1059    PHINode *PN;
1060    for (BasicBlock::iterator BBI = SI->begin();
1061         (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1062      Value *BB1V = PN->getIncomingValueForBlock(BB1);
1063      Value *BB2V = PN->getIncomingValueForBlock(BB2);
1064      if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
1065        return false;
1066      }
1067    }
1068  }
1069  return true;
1070}
1071
1072static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I);
1073
1074/// Given a conditional branch that goes to BB1 and BB2, hoist any common code
1075/// in the two blocks up into the branch block. The caller of this function
1076/// guarantees that BI's block dominates BB1 and BB2.
1077static bool HoistThenElseCodeToIf(BranchInst *BI,
1078                                  const TargetTransformInfo &TTI) {
1079  // This does very trivial matching, with limited scanning, to find identical
1080  // instructions in the two blocks.  In particular, we don't want to get into
1081  // O(M*N) situations here where M and N are the sizes of BB1 and BB2.  As
1082  // such, we currently just scan for obviously identical instructions in an
1083  // identical order.
1084  BasicBlock *BB1 = BI->getSuccessor(0);  // The true destination.
1085  BasicBlock *BB2 = BI->getSuccessor(1);  // The false destination
1086
1087  BasicBlock::iterator BB1_Itr = BB1->begin();
1088  BasicBlock::iterator BB2_Itr = BB2->begin();
1089
1090  Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
1091  // Skip debug info if it is not identical.
1092  DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1093  DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1094  if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1095    while (isa<DbgInfoIntrinsic>(I1))
1096      I1 = &*BB1_Itr++;
1097    while (isa<DbgInfoIntrinsic>(I2))
1098      I2 = &*BB2_Itr++;
1099  }
1100  if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1101      (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1102    return false;
1103
1104  BasicBlock *BIParent = BI->getParent();
1105
1106  bool Changed = false;
1107  do {
1108    // If we are hoisting the terminator instruction, don't move one (making a
1109    // broken BB), instead clone it, and remove BI.
1110    if (isa<TerminatorInst>(I1))
1111      goto HoistTerminator;
1112
1113    if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
1114      return Changed;
1115
1116    // For a normal instruction, we just move one to right before the branch,
1117    // then replace all uses of the other with the first.  Finally, we remove
1118    // the now redundant second instruction.
1119    BIParent->getInstList().splice(BI->getIterator(), BB1->getInstList(), I1);
1120    if (!I2->use_empty())
1121      I2->replaceAllUsesWith(I1);
1122    I1->intersectOptionalDataWith(I2);
1123    unsigned KnownIDs[] = {
1124        LLVMContext::MD_tbaa,    LLVMContext::MD_range,
1125        LLVMContext::MD_fpmath,  LLVMContext::MD_invariant_load,
1126        LLVMContext::MD_nonnull, LLVMContext::MD_invariant_group,
1127        LLVMContext::MD_align,   LLVMContext::MD_dereferenceable,
1128        LLVMContext::MD_dereferenceable_or_null};
1129    combineMetadata(I1, I2, KnownIDs);
1130    I2->eraseFromParent();
1131    Changed = true;
1132
1133    I1 = &*BB1_Itr++;
1134    I2 = &*BB2_Itr++;
1135    // Skip debug info if it is not identical.
1136    DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1137    DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1138    if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1139      while (isa<DbgInfoIntrinsic>(I1))
1140        I1 = &*BB1_Itr++;
1141      while (isa<DbgInfoIntrinsic>(I2))
1142        I2 = &*BB2_Itr++;
1143    }
1144  } while (I1->isIdenticalToWhenDefined(I2));
1145
1146  return true;
1147
1148HoistTerminator:
1149  // It may not be possible to hoist an invoke.
1150  if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1151    return Changed;
1152
1153  for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1154    PHINode *PN;
1155    for (BasicBlock::iterator BBI = SI->begin();
1156         (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1157      Value *BB1V = PN->getIncomingValueForBlock(BB1);
1158      Value *BB2V = PN->getIncomingValueForBlock(BB2);
1159      if (BB1V == BB2V)
1160        continue;
1161
1162      // Check for passingValueIsAlwaysUndefined here because we would rather
1163      // eliminate undefined control flow then converting it to a select.
1164      if (passingValueIsAlwaysUndefined(BB1V, PN) ||
1165          passingValueIsAlwaysUndefined(BB2V, PN))
1166       return Changed;
1167
1168      if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
1169        return Changed;
1170      if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
1171        return Changed;
1172    }
1173  }
1174
1175  // Okay, it is safe to hoist the terminator.
1176  Instruction *NT = I1->clone();
1177  BIParent->getInstList().insert(BI->getIterator(), NT);
1178  if (!NT->getType()->isVoidTy()) {
1179    I1->replaceAllUsesWith(NT);
1180    I2->replaceAllUsesWith(NT);
1181    NT->takeName(I1);
1182  }
1183
1184  IRBuilder<true, NoFolder> Builder(NT);
1185  // Hoisting one of the terminators from our successor is a great thing.
1186  // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1187  // them.  If they do, all PHI entries for BB1/BB2 must agree for all PHI
1188  // nodes, so we insert select instruction to compute the final result.
1189  std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
1190  for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1191    PHINode *PN;
1192    for (BasicBlock::iterator BBI = SI->begin();
1193         (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1194      Value *BB1V = PN->getIncomingValueForBlock(BB1);
1195      Value *BB2V = PN->getIncomingValueForBlock(BB2);
1196      if (BB1V == BB2V) continue;
1197
1198      // These values do not agree.  Insert a select instruction before NT
1199      // that determines the right value.
1200      SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1201      if (!SI)
1202        SI = cast<SelectInst>
1203          (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1204                                BB1V->getName()+"."+BB2V->getName()));
1205
1206      // Make the PHI node use the select for all incoming values for BB1/BB2
1207      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
1208        if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
1209          PN->setIncomingValue(i, SI);
1210    }
1211  }
1212
1213  // Update any PHI nodes in our new successors.
1214  for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
1215    AddPredecessorToBlock(*SI, BIParent, BB1);
1216
1217  EraseTerminatorInstAndDCECond(BI);
1218  return true;
1219}
1220
1221/// Given an unconditional branch that goes to BBEnd,
1222/// check whether BBEnd has only two predecessors and the other predecessor
1223/// ends with an unconditional branch. If it is true, sink any common code
1224/// in the two predecessors to BBEnd.
1225static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
1226  assert(BI1->isUnconditional());
1227  BasicBlock *BB1 = BI1->getParent();
1228  BasicBlock *BBEnd = BI1->getSuccessor(0);
1229
1230  // Check that BBEnd has two predecessors and the other predecessor ends with
1231  // an unconditional branch.
1232  pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd);
1233  BasicBlock *Pred0 = *PI++;
1234  if (PI == PE) // Only one predecessor.
1235    return false;
1236  BasicBlock *Pred1 = *PI++;
1237  if (PI != PE) // More than two predecessors.
1238    return false;
1239  BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0;
1240  BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
1241  if (!BI2 || !BI2->isUnconditional())
1242    return false;
1243
1244  // Gather the PHI nodes in BBEnd.
1245  SmallDenseMap<std::pair<Value *, Value *>, PHINode *> JointValueMap;
1246  Instruction *FirstNonPhiInBBEnd = nullptr;
1247  for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end(); I != E; ++I) {
1248    if (PHINode *PN = dyn_cast<PHINode>(I)) {
1249      Value *BB1V = PN->getIncomingValueForBlock(BB1);
1250      Value *BB2V = PN->getIncomingValueForBlock(BB2);
1251      JointValueMap[std::make_pair(BB1V, BB2V)] = PN;
1252    } else {
1253      FirstNonPhiInBBEnd = &*I;
1254      break;
1255    }
1256  }
1257  if (!FirstNonPhiInBBEnd)
1258    return false;
1259
1260  // This does very trivial matching, with limited scanning, to find identical
1261  // instructions in the two blocks.  We scan backward for obviously identical
1262  // instructions in an identical order.
1263  BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(),
1264                                             RE1 = BB1->getInstList().rend(),
1265                                             RI2 = BB2->getInstList().rbegin(),
1266                                             RE2 = BB2->getInstList().rend();
1267  // Skip debug info.
1268  while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1269  if (RI1 == RE1)
1270    return false;
1271  while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1272  if (RI2 == RE2)
1273    return false;
1274  // Skip the unconditional branches.
1275  ++RI1;
1276  ++RI2;
1277
1278  bool Changed = false;
1279  while (RI1 != RE1 && RI2 != RE2) {
1280    // Skip debug info.
1281    while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1282    if (RI1 == RE1)
1283      return Changed;
1284    while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1285    if (RI2 == RE2)
1286      return Changed;
1287
1288    Instruction *I1 = &*RI1, *I2 = &*RI2;
1289    auto InstPair = std::make_pair(I1, I2);
1290    // I1 and I2 should have a single use in the same PHI node, and they
1291    // perform the same operation.
1292    // Cannot move control-flow-involving, volatile loads, vaarg, etc.
1293    if (isa<PHINode>(I1) || isa<PHINode>(I2) ||
1294        isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) ||
1295        I1->isEHPad() || I2->isEHPad() ||
1296        isa<AllocaInst>(I1) || isa<AllocaInst>(I2) ||
1297        I1->mayHaveSideEffects() || I2->mayHaveSideEffects() ||
1298        I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() ||
1299        !I1->hasOneUse() || !I2->hasOneUse() ||
1300        !JointValueMap.count(InstPair))
1301      return Changed;
1302
1303    // Check whether we should swap the operands of ICmpInst.
1304    // TODO: Add support of communativity.
1305    ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2);
1306    bool SwapOpnds = false;
1307    if (ICmp1 && ICmp2 &&
1308        ICmp1->getOperand(0) != ICmp2->getOperand(0) &&
1309        ICmp1->getOperand(1) != ICmp2->getOperand(1) &&
1310        (ICmp1->getOperand(0) == ICmp2->getOperand(1) ||
1311         ICmp1->getOperand(1) == ICmp2->getOperand(0))) {
1312      ICmp2->swapOperands();
1313      SwapOpnds = true;
1314    }
1315    if (!I1->isSameOperationAs(I2)) {
1316      if (SwapOpnds)
1317        ICmp2->swapOperands();
1318      return Changed;
1319    }
1320
1321    // The operands should be either the same or they need to be generated
1322    // with a PHI node after sinking. We only handle the case where there is
1323    // a single pair of different operands.
1324    Value *DifferentOp1 = nullptr, *DifferentOp2 = nullptr;
1325    unsigned Op1Idx = ~0U;
1326    for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) {
1327      if (I1->getOperand(I) == I2->getOperand(I))
1328        continue;
1329      // Early exit if we have more-than one pair of different operands or if
1330      // we need a PHI node to replace a constant.
1331      if (Op1Idx != ~0U ||
1332          isa<Constant>(I1->getOperand(I)) ||
1333          isa<Constant>(I2->getOperand(I))) {
1334        // If we can't sink the instructions, undo the swapping.
1335        if (SwapOpnds)
1336          ICmp2->swapOperands();
1337        return Changed;
1338      }
1339      DifferentOp1 = I1->getOperand(I);
1340      Op1Idx = I;
1341      DifferentOp2 = I2->getOperand(I);
1342    }
1343
1344    DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n");
1345    DEBUG(dbgs() << "                         " << *I2 << "\n");
1346
1347    // We insert the pair of different operands to JointValueMap and
1348    // remove (I1, I2) from JointValueMap.
1349    if (Op1Idx != ~0U) {
1350      auto &NewPN = JointValueMap[std::make_pair(DifferentOp1, DifferentOp2)];
1351      if (!NewPN) {
1352        NewPN =
1353            PHINode::Create(DifferentOp1->getType(), 2,
1354                            DifferentOp1->getName() + ".sink", &BBEnd->front());
1355        NewPN->addIncoming(DifferentOp1, BB1);
1356        NewPN->addIncoming(DifferentOp2, BB2);
1357        DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";);
1358      }
1359      // I1 should use NewPN instead of DifferentOp1.
1360      I1->setOperand(Op1Idx, NewPN);
1361    }
1362    PHINode *OldPN = JointValueMap[InstPair];
1363    JointValueMap.erase(InstPair);
1364
1365    // We need to update RE1 and RE2 if we are going to sink the first
1366    // instruction in the basic block down.
1367    bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin());
1368    // Sink the instruction.
1369    BBEnd->getInstList().splice(FirstNonPhiInBBEnd->getIterator(),
1370                                BB1->getInstList(), I1);
1371    if (!OldPN->use_empty())
1372      OldPN->replaceAllUsesWith(I1);
1373    OldPN->eraseFromParent();
1374
1375    if (!I2->use_empty())
1376      I2->replaceAllUsesWith(I1);
1377    I1->intersectOptionalDataWith(I2);
1378    // TODO: Use combineMetadata here to preserve what metadata we can
1379    // (analogous to the hoisting case above).
1380    I2->eraseFromParent();
1381
1382    if (UpdateRE1)
1383      RE1 = BB1->getInstList().rend();
1384    if (UpdateRE2)
1385      RE2 = BB2->getInstList().rend();
1386    FirstNonPhiInBBEnd = &*I1;
1387    NumSinkCommons++;
1388    Changed = true;
1389  }
1390  return Changed;
1391}
1392
1393/// \brief Determine if we can hoist sink a sole store instruction out of a
1394/// conditional block.
1395///
1396/// We are looking for code like the following:
1397///   BrBB:
1398///     store i32 %add, i32* %arrayidx2
1399///     ... // No other stores or function calls (we could be calling a memory
1400///     ... // function).
1401///     %cmp = icmp ult %x, %y
1402///     br i1 %cmp, label %EndBB, label %ThenBB
1403///   ThenBB:
1404///     store i32 %add5, i32* %arrayidx2
1405///     br label EndBB
1406///   EndBB:
1407///     ...
1408///   We are going to transform this into:
1409///   BrBB:
1410///     store i32 %add, i32* %arrayidx2
1411///     ... //
1412///     %cmp = icmp ult %x, %y
1413///     %add.add5 = select i1 %cmp, i32 %add, %add5
1414///     store i32 %add.add5, i32* %arrayidx2
1415///     ...
1416///
1417/// \return The pointer to the value of the previous store if the store can be
1418///         hoisted into the predecessor block. 0 otherwise.
1419static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
1420                                     BasicBlock *StoreBB, BasicBlock *EndBB) {
1421  StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
1422  if (!StoreToHoist)
1423    return nullptr;
1424
1425  // Volatile or atomic.
1426  if (!StoreToHoist->isSimple())
1427    return nullptr;
1428
1429  Value *StorePtr = StoreToHoist->getPointerOperand();
1430
1431  // Look for a store to the same pointer in BrBB.
1432  unsigned MaxNumInstToLookAt = 10;
1433  for (BasicBlock::reverse_iterator RI = BrBB->rbegin(),
1434       RE = BrBB->rend(); RI != RE && (--MaxNumInstToLookAt); ++RI) {
1435    Instruction *CurI = &*RI;
1436
1437    // Could be calling an instruction that effects memory like free().
1438    if (CurI->mayHaveSideEffects() && !isa<StoreInst>(CurI))
1439      return nullptr;
1440
1441    StoreInst *SI = dyn_cast<StoreInst>(CurI);
1442    // Found the previous store make sure it stores to the same location.
1443    if (SI && SI->getPointerOperand() == StorePtr)
1444      // Found the previous store, return its value operand.
1445      return SI->getValueOperand();
1446    else if (SI)
1447      return nullptr; // Unknown store.
1448  }
1449
1450  return nullptr;
1451}
1452
1453/// \brief Speculate a conditional basic block flattening the CFG.
1454///
1455/// Note that this is a very risky transform currently. Speculating
1456/// instructions like this is most often not desirable. Instead, there is an MI
1457/// pass which can do it with full awareness of the resource constraints.
1458/// However, some cases are "obvious" and we should do directly. An example of
1459/// this is speculating a single, reasonably cheap instruction.
1460///
1461/// There is only one distinct advantage to flattening the CFG at the IR level:
1462/// it makes very common but simplistic optimizations such as are common in
1463/// instcombine and the DAG combiner more powerful by removing CFG edges and
1464/// modeling their effects with easier to reason about SSA value graphs.
1465///
1466///
1467/// An illustration of this transform is turning this IR:
1468/// \code
1469///   BB:
1470///     %cmp = icmp ult %x, %y
1471///     br i1 %cmp, label %EndBB, label %ThenBB
1472///   ThenBB:
1473///     %sub = sub %x, %y
1474///     br label BB2
1475///   EndBB:
1476///     %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
1477///     ...
1478/// \endcode
1479///
1480/// Into this IR:
1481/// \code
1482///   BB:
1483///     %cmp = icmp ult %x, %y
1484///     %sub = sub %x, %y
1485///     %cond = select i1 %cmp, 0, %sub
1486///     ...
1487/// \endcode
1488///
1489/// \returns true if the conditional block is removed.
1490static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
1491                                   const TargetTransformInfo &TTI) {
1492  // Be conservative for now. FP select instruction can often be expensive.
1493  Value *BrCond = BI->getCondition();
1494  if (isa<FCmpInst>(BrCond))
1495    return false;
1496
1497  BasicBlock *BB = BI->getParent();
1498  BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
1499
1500  // If ThenBB is actually on the false edge of the conditional branch, remember
1501  // to swap the select operands later.
1502  bool Invert = false;
1503  if (ThenBB != BI->getSuccessor(0)) {
1504    assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?");
1505    Invert = true;
1506  }
1507  assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block");
1508
1509  // Keep a count of how many times instructions are used within CondBB when
1510  // they are candidates for sinking into CondBB. Specifically:
1511  // - They are defined in BB, and
1512  // - They have no side effects, and
1513  // - All of their uses are in CondBB.
1514  SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
1515
1516  unsigned SpeculationCost = 0;
1517  Value *SpeculatedStoreValue = nullptr;
1518  StoreInst *SpeculatedStore = nullptr;
1519  for (BasicBlock::iterator BBI = ThenBB->begin(),
1520                            BBE = std::prev(ThenBB->end());
1521       BBI != BBE; ++BBI) {
1522    Instruction *I = &*BBI;
1523    // Skip debug info.
1524    if (isa<DbgInfoIntrinsic>(I))
1525      continue;
1526
1527    // Only speculatively execute a single instruction (not counting the
1528    // terminator) for now.
1529    ++SpeculationCost;
1530    if (SpeculationCost > 1)
1531      return false;
1532
1533    // Don't hoist the instruction if it's unsafe or expensive.
1534    if (!isSafeToSpeculativelyExecute(I) &&
1535        !(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore(
1536                                  I, BB, ThenBB, EndBB))))
1537      return false;
1538    if (!SpeculatedStoreValue &&
1539        ComputeSpeculationCost(I, TTI) >
1540            PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic)
1541      return false;
1542
1543    // Store the store speculation candidate.
1544    if (SpeculatedStoreValue)
1545      SpeculatedStore = cast<StoreInst>(I);
1546
1547    // Do not hoist the instruction if any of its operands are defined but not
1548    // used in BB. The transformation will prevent the operand from
1549    // being sunk into the use block.
1550    for (User::op_iterator i = I->op_begin(), e = I->op_end();
1551         i != e; ++i) {
1552      Instruction *OpI = dyn_cast<Instruction>(*i);
1553      if (!OpI || OpI->getParent() != BB ||
1554          OpI->mayHaveSideEffects())
1555        continue; // Not a candidate for sinking.
1556
1557      ++SinkCandidateUseCounts[OpI];
1558    }
1559  }
1560
1561  // Consider any sink candidates which are only used in CondBB as costs for
1562  // speculation. Note, while we iterate over a DenseMap here, we are summing
1563  // and so iteration order isn't significant.
1564  for (SmallDenseMap<Instruction *, unsigned, 4>::iterator I =
1565           SinkCandidateUseCounts.begin(), E = SinkCandidateUseCounts.end();
1566       I != E; ++I)
1567    if (I->first->getNumUses() == I->second) {
1568      ++SpeculationCost;
1569      if (SpeculationCost > 1)
1570        return false;
1571    }
1572
1573  // Check that the PHI nodes can be converted to selects.
1574  bool HaveRewritablePHIs = false;
1575  for (BasicBlock::iterator I = EndBB->begin();
1576       PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1577    Value *OrigV = PN->getIncomingValueForBlock(BB);
1578    Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
1579
1580    // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
1581    // Skip PHIs which are trivial.
1582    if (ThenV == OrigV)
1583      continue;
1584
1585    // Don't convert to selects if we could remove undefined behavior instead.
1586    if (passingValueIsAlwaysUndefined(OrigV, PN) ||
1587        passingValueIsAlwaysUndefined(ThenV, PN))
1588      return false;
1589
1590    HaveRewritablePHIs = true;
1591    ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
1592    ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
1593    if (!OrigCE && !ThenCE)
1594      continue; // Known safe and cheap.
1595
1596    if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
1597        (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
1598      return false;
1599    unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE, TTI) : 0;
1600    unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE, TTI) : 0;
1601    unsigned MaxCost = 2 * PHINodeFoldingThreshold *
1602      TargetTransformInfo::TCC_Basic;
1603    if (OrigCost + ThenCost > MaxCost)
1604      return false;
1605
1606    // Account for the cost of an unfolded ConstantExpr which could end up
1607    // getting expanded into Instructions.
1608    // FIXME: This doesn't account for how many operations are combined in the
1609    // constant expression.
1610    ++SpeculationCost;
1611    if (SpeculationCost > 1)
1612      return false;
1613  }
1614
1615  // If there are no PHIs to process, bail early. This helps ensure idempotence
1616  // as well.
1617  if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
1618    return false;
1619
1620  // If we get here, we can hoist the instruction and if-convert.
1621  DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";);
1622
1623  // Insert a select of the value of the speculated store.
1624  if (SpeculatedStoreValue) {
1625    IRBuilder<true, NoFolder> Builder(BI);
1626    Value *TrueV = SpeculatedStore->getValueOperand();
1627    Value *FalseV = SpeculatedStoreValue;
1628    if (Invert)
1629      std::swap(TrueV, FalseV);
1630    Value *S = Builder.CreateSelect(BrCond, TrueV, FalseV, TrueV->getName() +
1631                                    "." + FalseV->getName());
1632    SpeculatedStore->setOperand(0, S);
1633  }
1634
1635  // Metadata can be dependent on the condition we are hoisting above.
1636  // Conservatively strip all metadata on the instruction.
1637  for (auto &I: *ThenBB)
1638    I.dropUnknownNonDebugMetadata();
1639
1640  // Hoist the instructions.
1641  BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
1642                           ThenBB->begin(), std::prev(ThenBB->end()));
1643
1644  // Insert selects and rewrite the PHI operands.
1645  IRBuilder<true, NoFolder> Builder(BI);
1646  for (BasicBlock::iterator I = EndBB->begin();
1647       PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1648    unsigned OrigI = PN->getBasicBlockIndex(BB);
1649    unsigned ThenI = PN->getBasicBlockIndex(ThenBB);
1650    Value *OrigV = PN->getIncomingValue(OrigI);
1651    Value *ThenV = PN->getIncomingValue(ThenI);
1652
1653    // Skip PHIs which are trivial.
1654    if (OrigV == ThenV)
1655      continue;
1656
1657    // Create a select whose true value is the speculatively executed value and
1658    // false value is the preexisting value. Swap them if the branch
1659    // destinations were inverted.
1660    Value *TrueV = ThenV, *FalseV = OrigV;
1661    if (Invert)
1662      std::swap(TrueV, FalseV);
1663    Value *V = Builder.CreateSelect(BrCond, TrueV, FalseV,
1664                                    TrueV->getName() + "." + FalseV->getName());
1665    PN->setIncomingValue(OrigI, V);
1666    PN->setIncomingValue(ThenI, V);
1667  }
1668
1669  ++NumSpeculations;
1670  return true;
1671}
1672
1673/// \returns True if this block contains a CallInst with the NoDuplicate
1674/// attribute.
1675static bool HasNoDuplicateCall(const BasicBlock *BB) {
1676  for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1677    const CallInst *CI = dyn_cast<CallInst>(I);
1678    if (!CI)
1679      continue;
1680    if (CI->cannotDuplicate())
1681      return true;
1682  }
1683  return false;
1684}
1685
1686/// Return true if we can thread a branch across this block.
1687static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1688  BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1689  unsigned Size = 0;
1690
1691  for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1692    if (isa<DbgInfoIntrinsic>(BBI))
1693      continue;
1694    if (Size > 10) return false;  // Don't clone large BB's.
1695    ++Size;
1696
1697    // We can only support instructions that do not define values that are
1698    // live outside of the current basic block.
1699    for (User *U : BBI->users()) {
1700      Instruction *UI = cast<Instruction>(U);
1701      if (UI->getParent() != BB || isa<PHINode>(UI)) return false;
1702    }
1703
1704    // Looks ok, continue checking.
1705  }
1706
1707  return true;
1708}
1709
1710/// If we have a conditional branch on a PHI node value that is defined in the
1711/// same block as the branch and if any PHI entries are constants, thread edges
1712/// corresponding to that entry to be branches to their ultimate destination.
1713static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL) {
1714  BasicBlock *BB = BI->getParent();
1715  PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1716  // NOTE: we currently cannot transform this case if the PHI node is used
1717  // outside of the block.
1718  if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1719    return false;
1720
1721  // Degenerate case of a single entry PHI.
1722  if (PN->getNumIncomingValues() == 1) {
1723    FoldSingleEntryPHINodes(PN->getParent());
1724    return true;
1725  }
1726
1727  // Now we know that this block has multiple preds and two succs.
1728  if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1729
1730  if (HasNoDuplicateCall(BB)) return false;
1731
1732  // Okay, this is a simple enough basic block.  See if any phi values are
1733  // constants.
1734  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1735    ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1736    if (!CB || !CB->getType()->isIntegerTy(1)) continue;
1737
1738    // Okay, we now know that all edges from PredBB should be revectored to
1739    // branch to RealDest.
1740    BasicBlock *PredBB = PN->getIncomingBlock(i);
1741    BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1742
1743    if (RealDest == BB) continue;  // Skip self loops.
1744    // Skip if the predecessor's terminator is an indirect branch.
1745    if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1746
1747    // The dest block might have PHI nodes, other predecessors and other
1748    // difficult cases.  Instead of being smart about this, just insert a new
1749    // block that jumps to the destination block, effectively splitting
1750    // the edge we are about to create.
1751    BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1752                                            RealDest->getName()+".critedge",
1753                                            RealDest->getParent(), RealDest);
1754    BranchInst::Create(RealDest, EdgeBB);
1755
1756    // Update PHI nodes.
1757    AddPredecessorToBlock(RealDest, EdgeBB, BB);
1758
1759    // BB may have instructions that are being threaded over.  Clone these
1760    // instructions into EdgeBB.  We know that there will be no uses of the
1761    // cloned instructions outside of EdgeBB.
1762    BasicBlock::iterator InsertPt = EdgeBB->begin();
1763    DenseMap<Value*, Value*> TranslateMap;  // Track translated values.
1764    for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1765      if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1766        TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1767        continue;
1768      }
1769      // Clone the instruction.
1770      Instruction *N = BBI->clone();
1771      if (BBI->hasName()) N->setName(BBI->getName()+".c");
1772
1773      // Update operands due to translation.
1774      for (User::op_iterator i = N->op_begin(), e = N->op_end();
1775           i != e; ++i) {
1776        DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1777        if (PI != TranslateMap.end())
1778          *i = PI->second;
1779      }
1780
1781      // Check for trivial simplification.
1782      if (Value *V = SimplifyInstruction(N, DL)) {
1783        TranslateMap[&*BBI] = V;
1784        delete N;   // Instruction folded away, don't need actual inst
1785      } else {
1786        // Insert the new instruction into its new home.
1787        EdgeBB->getInstList().insert(InsertPt, N);
1788        if (!BBI->use_empty())
1789          TranslateMap[&*BBI] = N;
1790      }
1791    }
1792
1793    // Loop over all of the edges from PredBB to BB, changing them to branch
1794    // to EdgeBB instead.
1795    TerminatorInst *PredBBTI = PredBB->getTerminator();
1796    for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1797      if (PredBBTI->getSuccessor(i) == BB) {
1798        BB->removePredecessor(PredBB);
1799        PredBBTI->setSuccessor(i, EdgeBB);
1800      }
1801
1802    // Recurse, simplifying any other constants.
1803    return FoldCondBranchOnPHI(BI, DL) | true;
1804  }
1805
1806  return false;
1807}
1808
1809/// Given a BB that starts with the specified two-entry PHI node,
1810/// see if we can eliminate it.
1811static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
1812                                const DataLayout &DL) {
1813  // Ok, this is a two entry PHI node.  Check to see if this is a simple "if
1814  // statement", which has a very simple dominance structure.  Basically, we
1815  // are trying to find the condition that is being branched on, which
1816  // subsequently causes this merge to happen.  We really want control
1817  // dependence information for this check, but simplifycfg can't keep it up
1818  // to date, and this catches most of the cases we care about anyway.
1819  BasicBlock *BB = PN->getParent();
1820  BasicBlock *IfTrue, *IfFalse;
1821  Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1822  if (!IfCond ||
1823      // Don't bother if the branch will be constant folded trivially.
1824      isa<ConstantInt>(IfCond))
1825    return false;
1826
1827  // Okay, we found that we can merge this two-entry phi node into a select.
1828  // Doing so would require us to fold *all* two entry phi nodes in this block.
1829  // At some point this becomes non-profitable (particularly if the target
1830  // doesn't support cmov's).  Only do this transformation if there are two or
1831  // fewer PHI nodes in this block.
1832  unsigned NumPhis = 0;
1833  for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1834    if (NumPhis > 2)
1835      return false;
1836
1837  // Loop over the PHI's seeing if we can promote them all to select
1838  // instructions.  While we are at it, keep track of the instructions
1839  // that need to be moved to the dominating block.
1840  SmallPtrSet<Instruction*, 4> AggressiveInsts;
1841  unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1842           MaxCostVal1 = PHINodeFoldingThreshold;
1843  MaxCostVal0 *= TargetTransformInfo::TCC_Basic;
1844  MaxCostVal1 *= TargetTransformInfo::TCC_Basic;
1845
1846  for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1847    PHINode *PN = cast<PHINode>(II++);
1848    if (Value *V = SimplifyInstruction(PN, DL)) {
1849      PN->replaceAllUsesWith(V);
1850      PN->eraseFromParent();
1851      continue;
1852    }
1853
1854    if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1855                             MaxCostVal0, TTI) ||
1856        !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1857                             MaxCostVal1, TTI))
1858      return false;
1859  }
1860
1861  // If we folded the first phi, PN dangles at this point.  Refresh it.  If
1862  // we ran out of PHIs then we simplified them all.
1863  PN = dyn_cast<PHINode>(BB->begin());
1864  if (!PN) return true;
1865
1866  // Don't fold i1 branches on PHIs which contain binary operators.  These can
1867  // often be turned into switches and other things.
1868  if (PN->getType()->isIntegerTy(1) &&
1869      (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1870       isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1871       isa<BinaryOperator>(IfCond)))
1872    return false;
1873
1874  // If we all PHI nodes are promotable, check to make sure that all
1875  // instructions in the predecessor blocks can be promoted as well.  If
1876  // not, we won't be able to get rid of the control flow, so it's not
1877  // worth promoting to select instructions.
1878  BasicBlock *DomBlock = nullptr;
1879  BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1880  BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1881  if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1882    IfBlock1 = nullptr;
1883  } else {
1884    DomBlock = *pred_begin(IfBlock1);
1885    for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1886      if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
1887        // This is not an aggressive instruction that we can promote.
1888        // Because of this, we won't be able to get rid of the control
1889        // flow, so the xform is not worth it.
1890        return false;
1891      }
1892  }
1893
1894  if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1895    IfBlock2 = nullptr;
1896  } else {
1897    DomBlock = *pred_begin(IfBlock2);
1898    for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1899      if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I)) {
1900        // This is not an aggressive instruction that we can promote.
1901        // Because of this, we won't be able to get rid of the control
1902        // flow, so the xform is not worth it.
1903        return false;
1904      }
1905  }
1906
1907  DEBUG(dbgs() << "FOUND IF CONDITION!  " << *IfCond << "  T: "
1908               << IfTrue->getName() << "  F: " << IfFalse->getName() << "\n");
1909
1910  // If we can still promote the PHI nodes after this gauntlet of tests,
1911  // do all of the PHI's now.
1912  Instruction *InsertPt = DomBlock->getTerminator();
1913  IRBuilder<true, NoFolder> Builder(InsertPt);
1914
1915  // Move all 'aggressive' instructions, which are defined in the
1916  // conditional parts of the if's up to the dominating block.
1917  if (IfBlock1)
1918    DomBlock->getInstList().splice(InsertPt->getIterator(),
1919                                   IfBlock1->getInstList(), IfBlock1->begin(),
1920                                   IfBlock1->getTerminator()->getIterator());
1921  if (IfBlock2)
1922    DomBlock->getInstList().splice(InsertPt->getIterator(),
1923                                   IfBlock2->getInstList(), IfBlock2->begin(),
1924                                   IfBlock2->getTerminator()->getIterator());
1925
1926  while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1927    // Change the PHI node into a select instruction.
1928    Value *TrueVal  = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1929    Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1930
1931    SelectInst *NV =
1932      cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1933    PN->replaceAllUsesWith(NV);
1934    NV->takeName(PN);
1935    PN->eraseFromParent();
1936  }
1937
1938  // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1939  // has been flattened.  Change DomBlock to jump directly to our new block to
1940  // avoid other simplifycfg's kicking in on the diamond.
1941  TerminatorInst *OldTI = DomBlock->getTerminator();
1942  Builder.SetInsertPoint(OldTI);
1943  Builder.CreateBr(BB);
1944  OldTI->eraseFromParent();
1945  return true;
1946}
1947
1948/// If we found a conditional branch that goes to two returning blocks,
1949/// try to merge them together into one return,
1950/// introducing a select if the return values disagree.
1951static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1952                                           IRBuilder<> &Builder) {
1953  assert(BI->isConditional() && "Must be a conditional branch");
1954  BasicBlock *TrueSucc = BI->getSuccessor(0);
1955  BasicBlock *FalseSucc = BI->getSuccessor(1);
1956  ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1957  ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1958
1959  // Check to ensure both blocks are empty (just a return) or optionally empty
1960  // with PHI nodes.  If there are other instructions, merging would cause extra
1961  // computation on one path or the other.
1962  if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1963    return false;
1964  if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1965    return false;
1966
1967  Builder.SetInsertPoint(BI);
1968  // Okay, we found a branch that is going to two return nodes.  If
1969  // there is no return value for this function, just change the
1970  // branch into a return.
1971  if (FalseRet->getNumOperands() == 0) {
1972    TrueSucc->removePredecessor(BI->getParent());
1973    FalseSucc->removePredecessor(BI->getParent());
1974    Builder.CreateRetVoid();
1975    EraseTerminatorInstAndDCECond(BI);
1976    return true;
1977  }
1978
1979  // Otherwise, figure out what the true and false return values are
1980  // so we can insert a new select instruction.
1981  Value *TrueValue = TrueRet->getReturnValue();
1982  Value *FalseValue = FalseRet->getReturnValue();
1983
1984  // Unwrap any PHI nodes in the return blocks.
1985  if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1986    if (TVPN->getParent() == TrueSucc)
1987      TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1988  if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1989    if (FVPN->getParent() == FalseSucc)
1990      FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1991
1992  // In order for this transformation to be safe, we must be able to
1993  // unconditionally execute both operands to the return.  This is
1994  // normally the case, but we could have a potentially-trapping
1995  // constant expression that prevents this transformation from being
1996  // safe.
1997  if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1998    if (TCV->canTrap())
1999      return false;
2000  if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
2001    if (FCV->canTrap())
2002      return false;
2003
2004  // Okay, we collected all the mapped values and checked them for sanity, and
2005  // defined to really do this transformation.  First, update the CFG.
2006  TrueSucc->removePredecessor(BI->getParent());
2007  FalseSucc->removePredecessor(BI->getParent());
2008
2009  // Insert select instructions where needed.
2010  Value *BrCond = BI->getCondition();
2011  if (TrueValue) {
2012    // Insert a select if the results differ.
2013    if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
2014    } else if (isa<UndefValue>(TrueValue)) {
2015      TrueValue = FalseValue;
2016    } else {
2017      TrueValue = Builder.CreateSelect(BrCond, TrueValue,
2018                                       FalseValue, "retval");
2019    }
2020  }
2021
2022  Value *RI = !TrueValue ?
2023    Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
2024
2025  (void) RI;
2026
2027  DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
2028               << "\n  " << *BI << "NewRet = " << *RI
2029               << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
2030
2031  EraseTerminatorInstAndDCECond(BI);
2032
2033  return true;
2034}
2035
2036/// Given a conditional BranchInstruction, retrieve the probabilities of the
2037/// branch taking each edge. Fills in the two APInt parameters and returns true,
2038/// or returns false if no or invalid metadata was found.
2039static bool ExtractBranchMetadata(BranchInst *BI,
2040                                  uint64_t &ProbTrue, uint64_t &ProbFalse) {
2041  assert(BI->isConditional() &&
2042         "Looking for probabilities on unconditional branch?");
2043  MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
2044  if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
2045  ConstantInt *CITrue =
2046      mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(1));
2047  ConstantInt *CIFalse =
2048      mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(2));
2049  if (!CITrue || !CIFalse) return false;
2050  ProbTrue = CITrue->getValue().getZExtValue();
2051  ProbFalse = CIFalse->getValue().getZExtValue();
2052  return true;
2053}
2054
2055/// Return true if the given instruction is available
2056/// in its predecessor block. If yes, the instruction will be removed.
2057static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
2058  if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
2059    return false;
2060  for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
2061    Instruction *PBI = &*I;
2062    // Check whether Inst and PBI generate the same value.
2063    if (Inst->isIdenticalTo(PBI)) {
2064      Inst->replaceAllUsesWith(PBI);
2065      Inst->eraseFromParent();
2066      return true;
2067    }
2068  }
2069  return false;
2070}
2071
2072/// If this basic block is simple enough, and if a predecessor branches to us
2073/// and one of our successors, fold the block into the predecessor and use
2074/// logical operations to pick the right destination.
2075bool llvm::FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold) {
2076  BasicBlock *BB = BI->getParent();
2077
2078  Instruction *Cond = nullptr;
2079  if (BI->isConditional())
2080    Cond = dyn_cast<Instruction>(BI->getCondition());
2081  else {
2082    // For unconditional branch, check for a simple CFG pattern, where
2083    // BB has a single predecessor and BB's successor is also its predecessor's
2084    // successor. If such pattern exisits, check for CSE between BB and its
2085    // predecessor.
2086    if (BasicBlock *PB = BB->getSinglePredecessor())
2087      if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
2088        if (PBI->isConditional() &&
2089            (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
2090             BI->getSuccessor(0) == PBI->getSuccessor(1))) {
2091          for (BasicBlock::iterator I = BB->begin(), E = BB->end();
2092               I != E; ) {
2093            Instruction *Curr = &*I++;
2094            if (isa<CmpInst>(Curr)) {
2095              Cond = Curr;
2096              break;
2097            }
2098            // Quit if we can't remove this instruction.
2099            if (!checkCSEInPredecessor(Curr, PB))
2100              return false;
2101          }
2102        }
2103
2104    if (!Cond)
2105      return false;
2106  }
2107
2108  if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
2109      Cond->getParent() != BB || !Cond->hasOneUse())
2110  return false;
2111
2112  // Make sure the instruction after the condition is the cond branch.
2113  BasicBlock::iterator CondIt = ++Cond->getIterator();
2114
2115  // Ignore dbg intrinsics.
2116  while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
2117
2118  if (&*CondIt != BI)
2119    return false;
2120
2121  // Only allow this transformation if computing the condition doesn't involve
2122  // too many instructions and these involved instructions can be executed
2123  // unconditionally. We denote all involved instructions except the condition
2124  // as "bonus instructions", and only allow this transformation when the
2125  // number of the bonus instructions does not exceed a certain threshold.
2126  unsigned NumBonusInsts = 0;
2127  for (auto I = BB->begin(); Cond != I; ++I) {
2128    // Ignore dbg intrinsics.
2129    if (isa<DbgInfoIntrinsic>(I))
2130      continue;
2131    if (!I->hasOneUse() || !isSafeToSpeculativelyExecute(&*I))
2132      return false;
2133    // I has only one use and can be executed unconditionally.
2134    Instruction *User = dyn_cast<Instruction>(I->user_back());
2135    if (User == nullptr || User->getParent() != BB)
2136      return false;
2137    // I is used in the same BB. Since BI uses Cond and doesn't have more slots
2138    // to use any other instruction, User must be an instruction between next(I)
2139    // and Cond.
2140    ++NumBonusInsts;
2141    // Early exits once we reach the limit.
2142    if (NumBonusInsts > BonusInstThreshold)
2143      return false;
2144  }
2145
2146  // Cond is known to be a compare or binary operator.  Check to make sure that
2147  // neither operand is a potentially-trapping constant expression.
2148  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
2149    if (CE->canTrap())
2150      return false;
2151  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
2152    if (CE->canTrap())
2153      return false;
2154
2155  // Finally, don't infinitely unroll conditional loops.
2156  BasicBlock *TrueDest  = BI->getSuccessor(0);
2157  BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : nullptr;
2158  if (TrueDest == BB || FalseDest == BB)
2159    return false;
2160
2161  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2162    BasicBlock *PredBlock = *PI;
2163    BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
2164
2165    // Check that we have two conditional branches.  If there is a PHI node in
2166    // the common successor, verify that the same value flows in from both
2167    // blocks.
2168    SmallVector<PHINode*, 4> PHIs;
2169    if (!PBI || PBI->isUnconditional() ||
2170        (BI->isConditional() &&
2171         !SafeToMergeTerminators(BI, PBI)) ||
2172        (!BI->isConditional() &&
2173         !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
2174      continue;
2175
2176    // Determine if the two branches share a common destination.
2177    Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
2178    bool InvertPredCond = false;
2179
2180    if (BI->isConditional()) {
2181      if (PBI->getSuccessor(0) == TrueDest)
2182        Opc = Instruction::Or;
2183      else if (PBI->getSuccessor(1) == FalseDest)
2184        Opc = Instruction::And;
2185      else if (PBI->getSuccessor(0) == FalseDest)
2186        Opc = Instruction::And, InvertPredCond = true;
2187      else if (PBI->getSuccessor(1) == TrueDest)
2188        Opc = Instruction::Or, InvertPredCond = true;
2189      else
2190        continue;
2191    } else {
2192      if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
2193        continue;
2194    }
2195
2196    DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
2197    IRBuilder<> Builder(PBI);
2198
2199    // If we need to invert the condition in the pred block to match, do so now.
2200    if (InvertPredCond) {
2201      Value *NewCond = PBI->getCondition();
2202
2203      if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2204        CmpInst *CI = cast<CmpInst>(NewCond);
2205        CI->setPredicate(CI->getInversePredicate());
2206      } else {
2207        NewCond = Builder.CreateNot(NewCond,
2208                                    PBI->getCondition()->getName()+".not");
2209      }
2210
2211      PBI->setCondition(NewCond);
2212      PBI->swapSuccessors();
2213    }
2214
2215    // If we have bonus instructions, clone them into the predecessor block.
2216    // Note that there may be multiple predecessor blocks, so we cannot move
2217    // bonus instructions to a predecessor block.
2218    ValueToValueMapTy VMap; // maps original values to cloned values
2219    // We already make sure Cond is the last instruction before BI. Therefore,
2220    // all instructions before Cond other than DbgInfoIntrinsic are bonus
2221    // instructions.
2222    for (auto BonusInst = BB->begin(); Cond != BonusInst; ++BonusInst) {
2223      if (isa<DbgInfoIntrinsic>(BonusInst))
2224        continue;
2225      Instruction *NewBonusInst = BonusInst->clone();
2226      RemapInstruction(NewBonusInst, VMap,
2227                       RF_NoModuleLevelChanges | RF_IgnoreMissingEntries);
2228      VMap[&*BonusInst] = NewBonusInst;
2229
2230      // If we moved a load, we cannot any longer claim any knowledge about
2231      // its potential value. The previous information might have been valid
2232      // only given the branch precondition.
2233      // For an analogous reason, we must also drop all the metadata whose
2234      // semantics we don't understand.
2235      NewBonusInst->dropUnknownNonDebugMetadata();
2236
2237      PredBlock->getInstList().insert(PBI->getIterator(), NewBonusInst);
2238      NewBonusInst->takeName(&*BonusInst);
2239      BonusInst->setName(BonusInst->getName() + ".old");
2240    }
2241
2242    // Clone Cond into the predecessor basic block, and or/and the
2243    // two conditions together.
2244    Instruction *New = Cond->clone();
2245    RemapInstruction(New, VMap,
2246                     RF_NoModuleLevelChanges | RF_IgnoreMissingEntries);
2247    PredBlock->getInstList().insert(PBI->getIterator(), New);
2248    New->takeName(Cond);
2249    Cond->setName(New->getName() + ".old");
2250
2251    if (BI->isConditional()) {
2252      Instruction *NewCond =
2253        cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
2254                                            New, "or.cond"));
2255      PBI->setCondition(NewCond);
2256
2257      uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2258      bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2259                                                  PredFalseWeight);
2260      bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2261                                                  SuccFalseWeight);
2262      SmallVector<uint64_t, 8> NewWeights;
2263
2264      if (PBI->getSuccessor(0) == BB) {
2265        if (PredHasWeights && SuccHasWeights) {
2266          // PBI: br i1 %x, BB, FalseDest
2267          // BI:  br i1 %y, TrueDest, FalseDest
2268          //TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2269          NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2270          //FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2271          //               TrueWeight for PBI * FalseWeight for BI.
2272          // We assume that total weights of a BranchInst can fit into 32 bits.
2273          // Therefore, we will not have overflow using 64-bit arithmetic.
2274          NewWeights.push_back(PredFalseWeight * (SuccFalseWeight +
2275               SuccTrueWeight) + PredTrueWeight * SuccFalseWeight);
2276        }
2277        AddPredecessorToBlock(TrueDest, PredBlock, BB);
2278        PBI->setSuccessor(0, TrueDest);
2279      }
2280      if (PBI->getSuccessor(1) == BB) {
2281        if (PredHasWeights && SuccHasWeights) {
2282          // PBI: br i1 %x, TrueDest, BB
2283          // BI:  br i1 %y, TrueDest, FalseDest
2284          //TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2285          //              FalseWeight for PBI * TrueWeight for BI.
2286          NewWeights.push_back(PredTrueWeight * (SuccFalseWeight +
2287              SuccTrueWeight) + PredFalseWeight * SuccTrueWeight);
2288          //FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2289          NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2290        }
2291        AddPredecessorToBlock(FalseDest, PredBlock, BB);
2292        PBI->setSuccessor(1, FalseDest);
2293      }
2294      if (NewWeights.size() == 2) {
2295        // Halve the weights if any of them cannot fit in an uint32_t
2296        FitWeights(NewWeights);
2297
2298        SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end());
2299        PBI->setMetadata(LLVMContext::MD_prof,
2300                         MDBuilder(BI->getContext()).
2301                         createBranchWeights(MDWeights));
2302      } else
2303        PBI->setMetadata(LLVMContext::MD_prof, nullptr);
2304    } else {
2305      // Update PHI nodes in the common successors.
2306      for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2307        ConstantInt *PBI_C = cast<ConstantInt>(
2308          PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2309        assert(PBI_C->getType()->isIntegerTy(1));
2310        Instruction *MergedCond = nullptr;
2311        if (PBI->getSuccessor(0) == TrueDest) {
2312          // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2313          // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2314          //       is false: !PBI_Cond and BI_Value
2315          Instruction *NotCond =
2316            cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2317                                "not.cond"));
2318          MergedCond =
2319            cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2320                                NotCond, New,
2321                                "and.cond"));
2322          if (PBI_C->isOne())
2323            MergedCond =
2324              cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2325                                  PBI->getCondition(), MergedCond,
2326                                  "or.cond"));
2327        } else {
2328          // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2329          // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2330          //       is false: PBI_Cond and BI_Value
2331          MergedCond =
2332            cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2333                                PBI->getCondition(), New,
2334                                "and.cond"));
2335          if (PBI_C->isOne()) {
2336            Instruction *NotCond =
2337              cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2338                                  "not.cond"));
2339            MergedCond =
2340              cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2341                                  NotCond, MergedCond,
2342                                  "or.cond"));
2343          }
2344        }
2345        // Update PHI Node.
2346        PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2347                                  MergedCond);
2348      }
2349      // Change PBI from Conditional to Unconditional.
2350      BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2351      EraseTerminatorInstAndDCECond(PBI);
2352      PBI = New_PBI;
2353    }
2354
2355    // TODO: If BB is reachable from all paths through PredBlock, then we
2356    // could replace PBI's branch probabilities with BI's.
2357
2358    // Copy any debug value intrinsics into the end of PredBlock.
2359    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
2360      if (isa<DbgInfoIntrinsic>(*I))
2361        I->clone()->insertBefore(PBI);
2362
2363    return true;
2364  }
2365  return false;
2366}
2367
2368// If there is only one store in BB1 and BB2, return it, otherwise return
2369// nullptr.
2370static StoreInst *findUniqueStoreInBlocks(BasicBlock *BB1, BasicBlock *BB2) {
2371  StoreInst *S = nullptr;
2372  for (auto *BB : {BB1, BB2}) {
2373    if (!BB)
2374      continue;
2375    for (auto &I : *BB)
2376      if (auto *SI = dyn_cast<StoreInst>(&I)) {
2377        if (S)
2378          // Multiple stores seen.
2379          return nullptr;
2380        else
2381          S = SI;
2382      }
2383  }
2384  return S;
2385}
2386
2387static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
2388                                              Value *AlternativeV = nullptr) {
2389  // PHI is going to be a PHI node that allows the value V that is defined in
2390  // BB to be referenced in BB's only successor.
2391  //
2392  // If AlternativeV is nullptr, the only value we care about in PHI is V. It
2393  // doesn't matter to us what the other operand is (it'll never get used). We
2394  // could just create a new PHI with an undef incoming value, but that could
2395  // increase register pressure if EarlyCSE/InstCombine can't fold it with some
2396  // other PHI. So here we directly look for some PHI in BB's successor with V
2397  // as an incoming operand. If we find one, we use it, else we create a new
2398  // one.
2399  //
2400  // If AlternativeV is not nullptr, we care about both incoming values in PHI.
2401  // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV]
2402  // where OtherBB is the single other predecessor of BB's only successor.
2403  PHINode *PHI = nullptr;
2404  BasicBlock *Succ = BB->getSingleSuccessor();
2405
2406  for (auto I = Succ->begin(); isa<PHINode>(I); ++I)
2407    if (cast<PHINode>(I)->getIncomingValueForBlock(BB) == V) {
2408      PHI = cast<PHINode>(I);
2409      if (!AlternativeV)
2410        break;
2411
2412      assert(std::distance(pred_begin(Succ), pred_end(Succ)) == 2);
2413      auto PredI = pred_begin(Succ);
2414      BasicBlock *OtherPredBB = *PredI == BB ? *++PredI : *PredI;
2415      if (PHI->getIncomingValueForBlock(OtherPredBB) == AlternativeV)
2416        break;
2417      PHI = nullptr;
2418    }
2419  if (PHI)
2420    return PHI;
2421
2422  // If V is not an instruction defined in BB, just return it.
2423  if (!AlternativeV &&
2424      (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB))
2425    return V;
2426
2427  PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front());
2428  PHI->addIncoming(V, BB);
2429  for (BasicBlock *PredBB : predecessors(Succ))
2430    if (PredBB != BB)
2431      PHI->addIncoming(AlternativeV ? AlternativeV : UndefValue::get(V->getType()),
2432                       PredBB);
2433  return PHI;
2434}
2435
2436static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB,
2437                                           BasicBlock *QTB, BasicBlock *QFB,
2438                                           BasicBlock *PostBB, Value *Address,
2439                                           bool InvertPCond, bool InvertQCond) {
2440  auto IsaBitcastOfPointerType = [](const Instruction &I) {
2441    return Operator::getOpcode(&I) == Instruction::BitCast &&
2442           I.getType()->isPointerTy();
2443  };
2444
2445  // If we're not in aggressive mode, we only optimize if we have some
2446  // confidence that by optimizing we'll allow P and/or Q to be if-converted.
2447  auto IsWorthwhile = [&](BasicBlock *BB) {
2448    if (!BB)
2449      return true;
2450    // Heuristic: if the block can be if-converted/phi-folded and the
2451    // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
2452    // thread this store.
2453    unsigned N = 0;
2454    for (auto &I : *BB) {
2455      // Cheap instructions viable for folding.
2456      if (isa<BinaryOperator>(I) || isa<GetElementPtrInst>(I) ||
2457          isa<StoreInst>(I))
2458        ++N;
2459      // Free instructions.
2460      else if (isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) ||
2461               IsaBitcastOfPointerType(I))
2462        continue;
2463      else
2464        return false;
2465    }
2466    return N <= PHINodeFoldingThreshold;
2467  };
2468
2469  if (!MergeCondStoresAggressively && (!IsWorthwhile(PTB) ||
2470                                       !IsWorthwhile(PFB) ||
2471                                       !IsWorthwhile(QTB) ||
2472                                       !IsWorthwhile(QFB)))
2473    return false;
2474
2475  // For every pointer, there must be exactly two stores, one coming from
2476  // PTB or PFB, and the other from QTB or QFB. We don't support more than one
2477  // store (to any address) in PTB,PFB or QTB,QFB.
2478  // FIXME: We could relax this restriction with a bit more work and performance
2479  // testing.
2480  StoreInst *PStore = findUniqueStoreInBlocks(PTB, PFB);
2481  StoreInst *QStore = findUniqueStoreInBlocks(QTB, QFB);
2482  if (!PStore || !QStore)
2483    return false;
2484
2485  // Now check the stores are compatible.
2486  if (!QStore->isUnordered() || !PStore->isUnordered())
2487    return false;
2488
2489  // Check that sinking the store won't cause program behavior changes. Sinking
2490  // the store out of the Q blocks won't change any behavior as we're sinking
2491  // from a block to its unconditional successor. But we're moving a store from
2492  // the P blocks down through the middle block (QBI) and past both QFB and QTB.
2493  // So we need to check that there are no aliasing loads or stores in
2494  // QBI, QTB and QFB. We also need to check there are no conflicting memory
2495  // operations between PStore and the end of its parent block.
2496  //
2497  // The ideal way to do this is to query AliasAnalysis, but we don't
2498  // preserve AA currently so that is dangerous. Be super safe and just
2499  // check there are no other memory operations at all.
2500  for (auto &I : *QFB->getSinglePredecessor())
2501    if (I.mayReadOrWriteMemory())
2502      return false;
2503  for (auto &I : *QFB)
2504    if (&I != QStore && I.mayReadOrWriteMemory())
2505      return false;
2506  if (QTB)
2507    for (auto &I : *QTB)
2508      if (&I != QStore && I.mayReadOrWriteMemory())
2509        return false;
2510  for (auto I = BasicBlock::iterator(PStore), E = PStore->getParent()->end();
2511       I != E; ++I)
2512    if (&*I != PStore && I->mayReadOrWriteMemory())
2513      return false;
2514
2515  // OK, we're going to sink the stores to PostBB. The store has to be
2516  // conditional though, so first create the predicate.
2517  Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator())
2518                     ->getCondition();
2519  Value *QCond = cast<BranchInst>(QFB->getSinglePredecessor()->getTerminator())
2520                     ->getCondition();
2521
2522  Value *PPHI = ensureValueAvailableInSuccessor(PStore->getValueOperand(),
2523                                                PStore->getParent());
2524  Value *QPHI = ensureValueAvailableInSuccessor(QStore->getValueOperand(),
2525                                                QStore->getParent(), PPHI);
2526
2527  IRBuilder<> QB(&*PostBB->getFirstInsertionPt());
2528
2529  Value *PPred = PStore->getParent() == PTB ? PCond : QB.CreateNot(PCond);
2530  Value *QPred = QStore->getParent() == QTB ? QCond : QB.CreateNot(QCond);
2531
2532  if (InvertPCond)
2533    PPred = QB.CreateNot(PPred);
2534  if (InvertQCond)
2535    QPred = QB.CreateNot(QPred);
2536  Value *CombinedPred = QB.CreateOr(PPred, QPred);
2537
2538  auto *T =
2539      SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(), false);
2540  QB.SetInsertPoint(T);
2541  StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address));
2542  AAMDNodes AAMD;
2543  PStore->getAAMetadata(AAMD, /*Merge=*/false);
2544  PStore->getAAMetadata(AAMD, /*Merge=*/true);
2545  SI->setAAMetadata(AAMD);
2546
2547  QStore->eraseFromParent();
2548  PStore->eraseFromParent();
2549
2550  return true;
2551}
2552
2553static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI) {
2554  // The intention here is to find diamonds or triangles (see below) where each
2555  // conditional block contains a store to the same address. Both of these
2556  // stores are conditional, so they can't be unconditionally sunk. But it may
2557  // be profitable to speculatively sink the stores into one merged store at the
2558  // end, and predicate the merged store on the union of the two conditions of
2559  // PBI and QBI.
2560  //
2561  // This can reduce the number of stores executed if both of the conditions are
2562  // true, and can allow the blocks to become small enough to be if-converted.
2563  // This optimization will also chain, so that ladders of test-and-set
2564  // sequences can be if-converted away.
2565  //
2566  // We only deal with simple diamonds or triangles:
2567  //
2568  //     PBI       or      PBI        or a combination of the two
2569  //    /   \               | \
2570  //   PTB  PFB             |  PFB
2571  //    \   /               | /
2572  //     QBI                QBI
2573  //    /  \                | \
2574  //   QTB  QFB             |  QFB
2575  //    \  /                | /
2576  //    PostBB            PostBB
2577  //
2578  // We model triangles as a type of diamond with a nullptr "true" block.
2579  // Triangles are canonicalized so that the fallthrough edge is represented by
2580  // a true condition, as in the diagram above.
2581  //
2582  BasicBlock *PTB = PBI->getSuccessor(0);
2583  BasicBlock *PFB = PBI->getSuccessor(1);
2584  BasicBlock *QTB = QBI->getSuccessor(0);
2585  BasicBlock *QFB = QBI->getSuccessor(1);
2586  BasicBlock *PostBB = QFB->getSingleSuccessor();
2587
2588  bool InvertPCond = false, InvertQCond = false;
2589  // Canonicalize fallthroughs to the true branches.
2590  if (PFB == QBI->getParent()) {
2591    std::swap(PFB, PTB);
2592    InvertPCond = true;
2593  }
2594  if (QFB == PostBB) {
2595    std::swap(QFB, QTB);
2596    InvertQCond = true;
2597  }
2598
2599  // From this point on we can assume PTB or QTB may be fallthroughs but PFB
2600  // and QFB may not. Model fallthroughs as a nullptr block.
2601  if (PTB == QBI->getParent())
2602    PTB = nullptr;
2603  if (QTB == PostBB)
2604    QTB = nullptr;
2605
2606  // Legality bailouts. We must have at least the non-fallthrough blocks and
2607  // the post-dominating block, and the non-fallthroughs must only have one
2608  // predecessor.
2609  auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) {
2610    return BB->getSinglePredecessor() == P &&
2611           BB->getSingleSuccessor() == S;
2612  };
2613  if (!PostBB ||
2614      !HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
2615      !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB))
2616    return false;
2617  if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||
2618      (QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB)))
2619    return false;
2620  if (PostBB->getNumUses() != 2 || QBI->getParent()->getNumUses() != 2)
2621    return false;
2622
2623  // OK, this is a sequence of two diamonds or triangles.
2624  // Check if there are stores in PTB or PFB that are repeated in QTB or QFB.
2625  SmallPtrSet<Value *,4> PStoreAddresses, QStoreAddresses;
2626  for (auto *BB : {PTB, PFB}) {
2627    if (!BB)
2628      continue;
2629    for (auto &I : *BB)
2630      if (StoreInst *SI = dyn_cast<StoreInst>(&I))
2631        PStoreAddresses.insert(SI->getPointerOperand());
2632  }
2633  for (auto *BB : {QTB, QFB}) {
2634    if (!BB)
2635      continue;
2636    for (auto &I : *BB)
2637      if (StoreInst *SI = dyn_cast<StoreInst>(&I))
2638        QStoreAddresses.insert(SI->getPointerOperand());
2639  }
2640
2641  set_intersect(PStoreAddresses, QStoreAddresses);
2642  // set_intersect mutates PStoreAddresses in place. Rename it here to make it
2643  // clear what it contains.
2644  auto &CommonAddresses = PStoreAddresses;
2645
2646  bool Changed = false;
2647  for (auto *Address : CommonAddresses)
2648    Changed |= mergeConditionalStoreToAddress(
2649        PTB, PFB, QTB, QFB, PostBB, Address, InvertPCond, InvertQCond);
2650  return Changed;
2651}
2652
2653/// If we have a conditional branch as a predecessor of another block,
2654/// this function tries to simplify it.  We know
2655/// that PBI and BI are both conditional branches, and BI is in one of the
2656/// successor blocks of PBI - PBI branches to BI.
2657static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
2658                                           const DataLayout &DL) {
2659  assert(PBI->isConditional() && BI->isConditional());
2660  BasicBlock *BB = BI->getParent();
2661
2662  // If this block ends with a branch instruction, and if there is a
2663  // predecessor that ends on a branch of the same condition, make
2664  // this conditional branch redundant.
2665  if (PBI->getCondition() == BI->getCondition() &&
2666      PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2667    // Okay, the outcome of this conditional branch is statically
2668    // knowable.  If this block had a single pred, handle specially.
2669    if (BB->getSinglePredecessor()) {
2670      // Turn this into a branch on constant.
2671      bool CondIsTrue = PBI->getSuccessor(0) == BB;
2672      BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2673                                        CondIsTrue));
2674      return true;  // Nuke the branch on constant.
2675    }
2676
2677    // Otherwise, if there are multiple predecessors, insert a PHI that merges
2678    // in the constant and simplify the block result.  Subsequent passes of
2679    // simplifycfg will thread the block.
2680    if (BlockIsSimpleEnoughToThreadThrough(BB)) {
2681      pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
2682      PHINode *NewPN = PHINode::Create(
2683          Type::getInt1Ty(BB->getContext()), std::distance(PB, PE),
2684          BI->getCondition()->getName() + ".pr", &BB->front());
2685      // Okay, we're going to insert the PHI node.  Since PBI is not the only
2686      // predecessor, compute the PHI'd conditional value for all of the preds.
2687      // Any predecessor where the condition is not computable we keep symbolic.
2688      for (pred_iterator PI = PB; PI != PE; ++PI) {
2689        BasicBlock *P = *PI;
2690        if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
2691            PBI != BI && PBI->isConditional() &&
2692            PBI->getCondition() == BI->getCondition() &&
2693            PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2694          bool CondIsTrue = PBI->getSuccessor(0) == BB;
2695          NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2696                                              CondIsTrue), P);
2697        } else {
2698          NewPN->addIncoming(BI->getCondition(), P);
2699        }
2700      }
2701
2702      BI->setCondition(NewPN);
2703      return true;
2704    }
2705  }
2706
2707  if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
2708    if (CE->canTrap())
2709      return false;
2710
2711  // If BI is reached from the true path of PBI and PBI's condition implies
2712  // BI's condition, we know the direction of the BI branch.
2713  if (PBI->getSuccessor(0) == BI->getParent() &&
2714      isImpliedCondition(PBI->getCondition(), BI->getCondition(), DL) &&
2715      PBI->getSuccessor(0) != PBI->getSuccessor(1) &&
2716      BB->getSinglePredecessor()) {
2717    // Turn this into a branch on constant.
2718    auto *OldCond = BI->getCondition();
2719    BI->setCondition(ConstantInt::getTrue(BB->getContext()));
2720    RecursivelyDeleteTriviallyDeadInstructions(OldCond);
2721    return true;  // Nuke the branch on constant.
2722  }
2723
2724  // If both branches are conditional and both contain stores to the same
2725  // address, remove the stores from the conditionals and create a conditional
2726  // merged store at the end.
2727  if (MergeCondStores && mergeConditionalStores(PBI, BI))
2728    return true;
2729
2730  // If this is a conditional branch in an empty block, and if any
2731  // predecessors are a conditional branch to one of our destinations,
2732  // fold the conditions into logical ops and one cond br.
2733  BasicBlock::iterator BBI = BB->begin();
2734  // Ignore dbg intrinsics.
2735  while (isa<DbgInfoIntrinsic>(BBI))
2736    ++BBI;
2737  if (&*BBI != BI)
2738    return false;
2739
2740  int PBIOp, BIOp;
2741  if (PBI->getSuccessor(0) == BI->getSuccessor(0))
2742    PBIOp = BIOp = 0;
2743  else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
2744    PBIOp = 0, BIOp = 1;
2745  else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
2746    PBIOp = 1, BIOp = 0;
2747  else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
2748    PBIOp = BIOp = 1;
2749  else
2750    return false;
2751
2752  // Check to make sure that the other destination of this branch
2753  // isn't BB itself.  If so, this is an infinite loop that will
2754  // keep getting unwound.
2755  if (PBI->getSuccessor(PBIOp) == BB)
2756    return false;
2757
2758  // Do not perform this transformation if it would require
2759  // insertion of a large number of select instructions. For targets
2760  // without predication/cmovs, this is a big pessimization.
2761
2762  // Also do not perform this transformation if any phi node in the common
2763  // destination block can trap when reached by BB or PBB (PR17073). In that
2764  // case, it would be unsafe to hoist the operation into a select instruction.
2765
2766  BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
2767  unsigned NumPhis = 0;
2768  for (BasicBlock::iterator II = CommonDest->begin();
2769       isa<PHINode>(II); ++II, ++NumPhis) {
2770    if (NumPhis > 2) // Disable this xform.
2771      return false;
2772
2773    PHINode *PN = cast<PHINode>(II);
2774    Value *BIV = PN->getIncomingValueForBlock(BB);
2775    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV))
2776      if (CE->canTrap())
2777        return false;
2778
2779    unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2780    Value *PBIV = PN->getIncomingValue(PBBIdx);
2781    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV))
2782      if (CE->canTrap())
2783        return false;
2784  }
2785
2786  // Finally, if everything is ok, fold the branches to logical ops.
2787  BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
2788
2789  DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
2790               << "AND: " << *BI->getParent());
2791
2792
2793  // If OtherDest *is* BB, then BB is a basic block with a single conditional
2794  // branch in it, where one edge (OtherDest) goes back to itself but the other
2795  // exits.  We don't *know* that the program avoids the infinite loop
2796  // (even though that seems likely).  If we do this xform naively, we'll end up
2797  // recursively unpeeling the loop.  Since we know that (after the xform is
2798  // done) that the block *is* infinite if reached, we just make it an obviously
2799  // infinite loop with no cond branch.
2800  if (OtherDest == BB) {
2801    // Insert it at the end of the function, because it's either code,
2802    // or it won't matter if it's hot. :)
2803    BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
2804                                                  "infloop", BB->getParent());
2805    BranchInst::Create(InfLoopBlock, InfLoopBlock);
2806    OtherDest = InfLoopBlock;
2807  }
2808
2809  DEBUG(dbgs() << *PBI->getParent()->getParent());
2810
2811  // BI may have other predecessors.  Because of this, we leave
2812  // it alone, but modify PBI.
2813
2814  // Make sure we get to CommonDest on True&True directions.
2815  Value *PBICond = PBI->getCondition();
2816  IRBuilder<true, NoFolder> Builder(PBI);
2817  if (PBIOp)
2818    PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
2819
2820  Value *BICond = BI->getCondition();
2821  if (BIOp)
2822    BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
2823
2824  // Merge the conditions.
2825  Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
2826
2827  // Modify PBI to branch on the new condition to the new dests.
2828  PBI->setCondition(Cond);
2829  PBI->setSuccessor(0, CommonDest);
2830  PBI->setSuccessor(1, OtherDest);
2831
2832  // Update branch weight for PBI.
2833  uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2834  bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2835                                              PredFalseWeight);
2836  bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2837                                              SuccFalseWeight);
2838  if (PredHasWeights && SuccHasWeights) {
2839    uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
2840    uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
2841    uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
2842    uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
2843    // The weight to CommonDest should be PredCommon * SuccTotal +
2844    //                                    PredOther * SuccCommon.
2845    // The weight to OtherDest should be PredOther * SuccOther.
2846    uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
2847                                  PredOther * SuccCommon,
2848                              PredOther * SuccOther};
2849    // Halve the weights if any of them cannot fit in an uint32_t
2850    FitWeights(NewWeights);
2851
2852    PBI->setMetadata(LLVMContext::MD_prof,
2853                     MDBuilder(BI->getContext())
2854                         .createBranchWeights(NewWeights[0], NewWeights[1]));
2855  }
2856
2857  // OtherDest may have phi nodes.  If so, add an entry from PBI's
2858  // block that are identical to the entries for BI's block.
2859  AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
2860
2861  // We know that the CommonDest already had an edge from PBI to
2862  // it.  If it has PHIs though, the PHIs may have different
2863  // entries for BB and PBI's BB.  If so, insert a select to make
2864  // them agree.
2865  PHINode *PN;
2866  for (BasicBlock::iterator II = CommonDest->begin();
2867       (PN = dyn_cast<PHINode>(II)); ++II) {
2868    Value *BIV = PN->getIncomingValueForBlock(BB);
2869    unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2870    Value *PBIV = PN->getIncomingValue(PBBIdx);
2871    if (BIV != PBIV) {
2872      // Insert a select in PBI to pick the right value.
2873      Value *NV = cast<SelectInst>
2874        (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
2875      PN->setIncomingValue(PBBIdx, NV);
2876    }
2877  }
2878
2879  DEBUG(dbgs() << "INTO: " << *PBI->getParent());
2880  DEBUG(dbgs() << *PBI->getParent()->getParent());
2881
2882  // This basic block is probably dead.  We know it has at least
2883  // one fewer predecessor.
2884  return true;
2885}
2886
2887// Simplifies a terminator by replacing it with a branch to TrueBB if Cond is
2888// true or to FalseBB if Cond is false.
2889// Takes care of updating the successors and removing the old terminator.
2890// Also makes sure not to introduce new successors by assuming that edges to
2891// non-successor TrueBBs and FalseBBs aren't reachable.
2892static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
2893                                       BasicBlock *TrueBB, BasicBlock *FalseBB,
2894                                       uint32_t TrueWeight,
2895                                       uint32_t FalseWeight){
2896  // Remove any superfluous successor edges from the CFG.
2897  // First, figure out which successors to preserve.
2898  // If TrueBB and FalseBB are equal, only try to preserve one copy of that
2899  // successor.
2900  BasicBlock *KeepEdge1 = TrueBB;
2901  BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
2902
2903  // Then remove the rest.
2904  for (BasicBlock *Succ : OldTerm->successors()) {
2905    // Make sure only to keep exactly one copy of each edge.
2906    if (Succ == KeepEdge1)
2907      KeepEdge1 = nullptr;
2908    else if (Succ == KeepEdge2)
2909      KeepEdge2 = nullptr;
2910    else
2911      Succ->removePredecessor(OldTerm->getParent(),
2912                              /*DontDeleteUselessPHIs=*/true);
2913  }
2914
2915  IRBuilder<> Builder(OldTerm);
2916  Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
2917
2918  // Insert an appropriate new terminator.
2919  if (!KeepEdge1 && !KeepEdge2) {
2920    if (TrueBB == FalseBB)
2921      // We were only looking for one successor, and it was present.
2922      // Create an unconditional branch to it.
2923      Builder.CreateBr(TrueBB);
2924    else {
2925      // We found both of the successors we were looking for.
2926      // Create a conditional branch sharing the condition of the select.
2927      BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
2928      if (TrueWeight != FalseWeight)
2929        NewBI->setMetadata(LLVMContext::MD_prof,
2930                           MDBuilder(OldTerm->getContext()).
2931                           createBranchWeights(TrueWeight, FalseWeight));
2932    }
2933  } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
2934    // Neither of the selected blocks were successors, so this
2935    // terminator must be unreachable.
2936    new UnreachableInst(OldTerm->getContext(), OldTerm);
2937  } else {
2938    // One of the selected values was a successor, but the other wasn't.
2939    // Insert an unconditional branch to the one that was found;
2940    // the edge to the one that wasn't must be unreachable.
2941    if (!KeepEdge1)
2942      // Only TrueBB was found.
2943      Builder.CreateBr(TrueBB);
2944    else
2945      // Only FalseBB was found.
2946      Builder.CreateBr(FalseBB);
2947  }
2948
2949  EraseTerminatorInstAndDCECond(OldTerm);
2950  return true;
2951}
2952
2953// Replaces
2954//   (switch (select cond, X, Y)) on constant X, Y
2955// with a branch - conditional if X and Y lead to distinct BBs,
2956// unconditional otherwise.
2957static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2958  // Check for constant integer values in the select.
2959  ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2960  ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2961  if (!TrueVal || !FalseVal)
2962    return false;
2963
2964  // Find the relevant condition and destinations.
2965  Value *Condition = Select->getCondition();
2966  BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2967  BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2968
2969  // Get weight for TrueBB and FalseBB.
2970  uint32_t TrueWeight = 0, FalseWeight = 0;
2971  SmallVector<uint64_t, 8> Weights;
2972  bool HasWeights = HasBranchWeights(SI);
2973  if (HasWeights) {
2974    GetBranchWeights(SI, Weights);
2975    if (Weights.size() == 1 + SI->getNumCases()) {
2976      TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal).
2977                                     getSuccessorIndex()];
2978      FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal).
2979                                      getSuccessorIndex()];
2980    }
2981  }
2982
2983  // Perform the actual simplification.
2984  return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB,
2985                                    TrueWeight, FalseWeight);
2986}
2987
2988// Replaces
2989//   (indirectbr (select cond, blockaddress(@fn, BlockA),
2990//                             blockaddress(@fn, BlockB)))
2991// with
2992//   (br cond, BlockA, BlockB).
2993static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2994  // Check that both operands of the select are block addresses.
2995  BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2996  BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2997  if (!TBA || !FBA)
2998    return false;
2999
3000  // Extract the actual blocks.
3001  BasicBlock *TrueBB = TBA->getBasicBlock();
3002  BasicBlock *FalseBB = FBA->getBasicBlock();
3003
3004  // Perform the actual simplification.
3005  return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB,
3006                                    0, 0);
3007}
3008
3009/// This is called when we find an icmp instruction
3010/// (a seteq/setne with a constant) as the only instruction in a
3011/// block that ends with an uncond branch.  We are looking for a very specific
3012/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified.  In
3013/// this case, we merge the first two "or's of icmp" into a switch, but then the
3014/// default value goes to an uncond block with a seteq in it, we get something
3015/// like:
3016///
3017///   switch i8 %A, label %DEFAULT [ i8 1, label %end    i8 2, label %end ]
3018/// DEFAULT:
3019///   %tmp = icmp eq i8 %A, 92
3020///   br label %end
3021/// end:
3022///   ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
3023///
3024/// We prefer to split the edge to 'end' so that there is a true/false entry to
3025/// the PHI, merging the third icmp into the switch.
3026static bool TryToSimplifyUncondBranchWithICmpInIt(
3027    ICmpInst *ICI, IRBuilder<> &Builder, const DataLayout &DL,
3028    const TargetTransformInfo &TTI, unsigned BonusInstThreshold,
3029    AssumptionCache *AC) {
3030  BasicBlock *BB = ICI->getParent();
3031
3032  // If the block has any PHIs in it or the icmp has multiple uses, it is too
3033  // complex.
3034  if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
3035
3036  Value *V = ICI->getOperand(0);
3037  ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
3038
3039  // The pattern we're looking for is where our only predecessor is a switch on
3040  // 'V' and this block is the default case for the switch.  In this case we can
3041  // fold the compared value into the switch to simplify things.
3042  BasicBlock *Pred = BB->getSinglePredecessor();
3043  if (!Pred || !isa<SwitchInst>(Pred->getTerminator())) return false;
3044
3045  SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
3046  if (SI->getCondition() != V)
3047    return false;
3048
3049  // If BB is reachable on a non-default case, then we simply know the value of
3050  // V in this block.  Substitute it and constant fold the icmp instruction
3051  // away.
3052  if (SI->getDefaultDest() != BB) {
3053    ConstantInt *VVal = SI->findCaseDest(BB);
3054    assert(VVal && "Should have a unique destination value");
3055    ICI->setOperand(0, VVal);
3056
3057    if (Value *V = SimplifyInstruction(ICI, DL)) {
3058      ICI->replaceAllUsesWith(V);
3059      ICI->eraseFromParent();
3060    }
3061    // BB is now empty, so it is likely to simplify away.
3062    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
3063  }
3064
3065  // Ok, the block is reachable from the default dest.  If the constant we're
3066  // comparing exists in one of the other edges, then we can constant fold ICI
3067  // and zap it.
3068  if (SI->findCaseValue(Cst) != SI->case_default()) {
3069    Value *V;
3070    if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
3071      V = ConstantInt::getFalse(BB->getContext());
3072    else
3073      V = ConstantInt::getTrue(BB->getContext());
3074
3075    ICI->replaceAllUsesWith(V);
3076    ICI->eraseFromParent();
3077    // BB is now empty, so it is likely to simplify away.
3078    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
3079  }
3080
3081  // The use of the icmp has to be in the 'end' block, by the only PHI node in
3082  // the block.
3083  BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
3084  PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back());
3085  if (PHIUse == nullptr || PHIUse != &SuccBlock->front() ||
3086      isa<PHINode>(++BasicBlock::iterator(PHIUse)))
3087    return false;
3088
3089  // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
3090  // true in the PHI.
3091  Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
3092  Constant *NewCst     = ConstantInt::getFalse(BB->getContext());
3093
3094  if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
3095    std::swap(DefaultCst, NewCst);
3096
3097  // Replace ICI (which is used by the PHI for the default value) with true or
3098  // false depending on if it is EQ or NE.
3099  ICI->replaceAllUsesWith(DefaultCst);
3100  ICI->eraseFromParent();
3101
3102  // Okay, the switch goes to this block on a default value.  Add an edge from
3103  // the switch to the merge point on the compared value.
3104  BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
3105                                         BB->getParent(), BB);
3106  SmallVector<uint64_t, 8> Weights;
3107  bool HasWeights = HasBranchWeights(SI);
3108  if (HasWeights) {
3109    GetBranchWeights(SI, Weights);
3110    if (Weights.size() == 1 + SI->getNumCases()) {
3111      // Split weight for default case to case for "Cst".
3112      Weights[0] = (Weights[0]+1) >> 1;
3113      Weights.push_back(Weights[0]);
3114
3115      SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3116      SI->setMetadata(LLVMContext::MD_prof,
3117                      MDBuilder(SI->getContext()).
3118                      createBranchWeights(MDWeights));
3119    }
3120  }
3121  SI->addCase(Cst, NewBB);
3122
3123  // NewBB branches to the phi block, add the uncond branch and the phi entry.
3124  Builder.SetInsertPoint(NewBB);
3125  Builder.SetCurrentDebugLocation(SI->getDebugLoc());
3126  Builder.CreateBr(SuccBlock);
3127  PHIUse->addIncoming(NewCst, NewBB);
3128  return true;
3129}
3130
3131/// The specified branch is a conditional branch.
3132/// Check to see if it is branching on an or/and chain of icmp instructions, and
3133/// fold it into a switch instruction if so.
3134static bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
3135                                      const DataLayout &DL) {
3136  Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
3137  if (!Cond) return false;
3138
3139  // Change br (X == 0 | X == 1), T, F into a switch instruction.
3140  // If this is a bunch of seteq's or'd together, or if it's a bunch of
3141  // 'setne's and'ed together, collect them.
3142
3143  // Try to gather values from a chain of and/or to be turned into a switch
3144  ConstantComparesGatherer ConstantCompare(Cond, DL);
3145  // Unpack the result
3146  SmallVectorImpl<ConstantInt*> &Values = ConstantCompare.Vals;
3147  Value *CompVal = ConstantCompare.CompValue;
3148  unsigned UsedICmps = ConstantCompare.UsedICmps;
3149  Value *ExtraCase = ConstantCompare.Extra;
3150
3151  // If we didn't have a multiply compared value, fail.
3152  if (!CompVal) return false;
3153
3154  // Avoid turning single icmps into a switch.
3155  if (UsedICmps <= 1)
3156    return false;
3157
3158  bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);
3159
3160  // There might be duplicate constants in the list, which the switch
3161  // instruction can't handle, remove them now.
3162  array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
3163  Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
3164
3165  // If Extra was used, we require at least two switch values to do the
3166  // transformation.  A switch with one value is just a conditional branch.
3167  if (ExtraCase && Values.size() < 2) return false;
3168
3169  // TODO: Preserve branch weight metadata, similarly to how
3170  // FoldValueComparisonIntoPredecessors preserves it.
3171
3172  // Figure out which block is which destination.
3173  BasicBlock *DefaultBB = BI->getSuccessor(1);
3174  BasicBlock *EdgeBB    = BI->getSuccessor(0);
3175  if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
3176
3177  BasicBlock *BB = BI->getParent();
3178
3179  DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
3180               << " cases into SWITCH.  BB is:\n" << *BB);
3181
3182  // If there are any extra values that couldn't be folded into the switch
3183  // then we evaluate them with an explicit branch first.  Split the block
3184  // right before the condbr to handle it.
3185  if (ExtraCase) {
3186    BasicBlock *NewBB =
3187        BB->splitBasicBlock(BI->getIterator(), "switch.early.test");
3188    // Remove the uncond branch added to the old block.
3189    TerminatorInst *OldTI = BB->getTerminator();
3190    Builder.SetInsertPoint(OldTI);
3191
3192    if (TrueWhenEqual)
3193      Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
3194    else
3195      Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
3196
3197    OldTI->eraseFromParent();
3198
3199    // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
3200    // for the edge we just added.
3201    AddPredecessorToBlock(EdgeBB, BB, NewBB);
3202
3203    DEBUG(dbgs() << "  ** 'icmp' chain unhandled condition: " << *ExtraCase
3204          << "\nEXTRABB = " << *BB);
3205    BB = NewBB;
3206  }
3207
3208  Builder.SetInsertPoint(BI);
3209  // Convert pointer to int before we switch.
3210  if (CompVal->getType()->isPointerTy()) {
3211    CompVal = Builder.CreatePtrToInt(
3212        CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr");
3213  }
3214
3215  // Create the new switch instruction now.
3216  SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
3217
3218  // Add all of the 'cases' to the switch instruction.
3219  for (unsigned i = 0, e = Values.size(); i != e; ++i)
3220    New->addCase(Values[i], EdgeBB);
3221
3222  // We added edges from PI to the EdgeBB.  As such, if there were any
3223  // PHI nodes in EdgeBB, they need entries to be added corresponding to
3224  // the number of edges added.
3225  for (BasicBlock::iterator BBI = EdgeBB->begin();
3226       isa<PHINode>(BBI); ++BBI) {
3227    PHINode *PN = cast<PHINode>(BBI);
3228    Value *InVal = PN->getIncomingValueForBlock(BB);
3229    for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
3230      PN->addIncoming(InVal, BB);
3231  }
3232
3233  // Erase the old branch instruction.
3234  EraseTerminatorInstAndDCECond(BI);
3235
3236  DEBUG(dbgs() << "  ** 'icmp' chain result is:\n" << *BB << '\n');
3237  return true;
3238}
3239
3240bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
3241  // If this is a trivial landing pad that just continues unwinding the caught
3242  // exception then zap the landing pad, turning its invokes into calls.
3243  BasicBlock *BB = RI->getParent();
3244  LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
3245  if (RI->getValue() != LPInst)
3246    // Not a landing pad, or the resume is not unwinding the exception that
3247    // caused control to branch here.
3248    return false;
3249
3250  // Check that there are no other instructions except for debug intrinsics.
3251  BasicBlock::iterator I = LPInst->getIterator(), E = RI->getIterator();
3252  while (++I != E)
3253    if (!isa<DbgInfoIntrinsic>(I))
3254      return false;
3255
3256  // Turn all invokes that unwind here into calls and delete the basic block.
3257  for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3258    BasicBlock *Pred = *PI++;
3259    removeUnwindEdge(Pred);
3260  }
3261
3262  // The landingpad is now unreachable.  Zap it.
3263  BB->eraseFromParent();
3264  return true;
3265}
3266
3267bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
3268  // If this is a trivial cleanup pad that executes no instructions, it can be
3269  // eliminated.  If the cleanup pad continues to the caller, any predecessor
3270  // that is an EH pad will be updated to continue to the caller and any
3271  // predecessor that terminates with an invoke instruction will have its invoke
3272  // instruction converted to a call instruction.  If the cleanup pad being
3273  // simplified does not continue to the caller, each predecessor will be
3274  // updated to continue to the unwind destination of the cleanup pad being
3275  // simplified.
3276  BasicBlock *BB = RI->getParent();
3277  CleanupPadInst *CPInst = RI->getCleanupPad();
3278  if (CPInst->getParent() != BB)
3279    // This isn't an empty cleanup.
3280    return false;
3281
3282  // Check that there are no other instructions except for debug intrinsics.
3283  BasicBlock::iterator I = CPInst->getIterator(), E = RI->getIterator();
3284  while (++I != E)
3285    if (!isa<DbgInfoIntrinsic>(I))
3286      return false;
3287
3288  // If the cleanup return we are simplifying unwinds to the caller, this will
3289  // set UnwindDest to nullptr.
3290  BasicBlock *UnwindDest = RI->getUnwindDest();
3291  Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr;
3292
3293  // We're about to remove BB from the control flow.  Before we do, sink any
3294  // PHINodes into the unwind destination.  Doing this before changing the
3295  // control flow avoids some potentially slow checks, since we can currently
3296  // be certain that UnwindDest and BB have no common predecessors (since they
3297  // are both EH pads).
3298  if (UnwindDest) {
3299    // First, go through the PHI nodes in UnwindDest and update any nodes that
3300    // reference the block we are removing
3301    for (BasicBlock::iterator I = UnwindDest->begin(),
3302                              IE = DestEHPad->getIterator();
3303         I != IE; ++I) {
3304      PHINode *DestPN = cast<PHINode>(I);
3305
3306      int Idx = DestPN->getBasicBlockIndex(BB);
3307      // Since BB unwinds to UnwindDest, it has to be in the PHI node.
3308      assert(Idx != -1);
3309      // This PHI node has an incoming value that corresponds to a control
3310      // path through the cleanup pad we are removing.  If the incoming
3311      // value is in the cleanup pad, it must be a PHINode (because we
3312      // verified above that the block is otherwise empty).  Otherwise, the
3313      // value is either a constant or a value that dominates the cleanup
3314      // pad being removed.
3315      //
3316      // Because BB and UnwindDest are both EH pads, all of their
3317      // predecessors must unwind to these blocks, and since no instruction
3318      // can have multiple unwind destinations, there will be no overlap in
3319      // incoming blocks between SrcPN and DestPN.
3320      Value *SrcVal = DestPN->getIncomingValue(Idx);
3321      PHINode *SrcPN = dyn_cast<PHINode>(SrcVal);
3322
3323      // Remove the entry for the block we are deleting.
3324      DestPN->removeIncomingValue(Idx, false);
3325
3326      if (SrcPN && SrcPN->getParent() == BB) {
3327        // If the incoming value was a PHI node in the cleanup pad we are
3328        // removing, we need to merge that PHI node's incoming values into
3329        // DestPN.
3330        for (unsigned SrcIdx = 0, SrcE = SrcPN->getNumIncomingValues();
3331              SrcIdx != SrcE; ++SrcIdx) {
3332          DestPN->addIncoming(SrcPN->getIncomingValue(SrcIdx),
3333                              SrcPN->getIncomingBlock(SrcIdx));
3334        }
3335      } else {
3336        // Otherwise, the incoming value came from above BB and
3337        // so we can just reuse it.  We must associate all of BB's
3338        // predecessors with this value.
3339        for (auto *pred : predecessors(BB)) {
3340          DestPN->addIncoming(SrcVal, pred);
3341        }
3342      }
3343    }
3344
3345    // Sink any remaining PHI nodes directly into UnwindDest.
3346    Instruction *InsertPt = DestEHPad;
3347    for (BasicBlock::iterator I = BB->begin(),
3348                              IE = BB->getFirstNonPHI()->getIterator();
3349         I != IE;) {
3350      // The iterator must be incremented here because the instructions are
3351      // being moved to another block.
3352      PHINode *PN = cast<PHINode>(I++);
3353      if (PN->use_empty())
3354        // If the PHI node has no uses, just leave it.  It will be erased
3355        // when we erase BB below.
3356        continue;
3357
3358      // Otherwise, sink this PHI node into UnwindDest.
3359      // Any predecessors to UnwindDest which are not already represented
3360      // must be back edges which inherit the value from the path through
3361      // BB.  In this case, the PHI value must reference itself.
3362      for (auto *pred : predecessors(UnwindDest))
3363        if (pred != BB)
3364          PN->addIncoming(PN, pred);
3365      PN->moveBefore(InsertPt);
3366    }
3367  }
3368
3369  for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
3370    // The iterator must be updated here because we are removing this pred.
3371    BasicBlock *PredBB = *PI++;
3372    if (UnwindDest == nullptr) {
3373      removeUnwindEdge(PredBB);
3374    } else {
3375      TerminatorInst *TI = PredBB->getTerminator();
3376      TI->replaceUsesOfWith(BB, UnwindDest);
3377    }
3378  }
3379
3380  // The cleanup pad is now unreachable.  Zap it.
3381  BB->eraseFromParent();
3382  return true;
3383}
3384
3385bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
3386  BasicBlock *BB = RI->getParent();
3387  if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
3388
3389  // Find predecessors that end with branches.
3390  SmallVector<BasicBlock*, 8> UncondBranchPreds;
3391  SmallVector<BranchInst*, 8> CondBranchPreds;
3392  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
3393    BasicBlock *P = *PI;
3394    TerminatorInst *PTI = P->getTerminator();
3395    if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
3396      if (BI->isUnconditional())
3397        UncondBranchPreds.push_back(P);
3398      else
3399        CondBranchPreds.push_back(BI);
3400    }
3401  }
3402
3403  // If we found some, do the transformation!
3404  if (!UncondBranchPreds.empty() && DupRet) {
3405    while (!UncondBranchPreds.empty()) {
3406      BasicBlock *Pred = UncondBranchPreds.pop_back_val();
3407      DEBUG(dbgs() << "FOLDING: " << *BB
3408            << "INTO UNCOND BRANCH PRED: " << *Pred);
3409      (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
3410    }
3411
3412    // If we eliminated all predecessors of the block, delete the block now.
3413    if (pred_empty(BB))
3414      // We know there are no successors, so just nuke the block.
3415      BB->eraseFromParent();
3416
3417    return true;
3418  }
3419
3420  // Check out all of the conditional branches going to this return
3421  // instruction.  If any of them just select between returns, change the
3422  // branch itself into a select/return pair.
3423  while (!CondBranchPreds.empty()) {
3424    BranchInst *BI = CondBranchPreds.pop_back_val();
3425
3426    // Check to see if the non-BB successor is also a return block.
3427    if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
3428        isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
3429        SimplifyCondBranchToTwoReturns(BI, Builder))
3430      return true;
3431  }
3432  return false;
3433}
3434
3435bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
3436  BasicBlock *BB = UI->getParent();
3437
3438  bool Changed = false;
3439
3440  // If there are any instructions immediately before the unreachable that can
3441  // be removed, do so.
3442  while (UI->getIterator() != BB->begin()) {
3443    BasicBlock::iterator BBI = UI->getIterator();
3444    --BBI;
3445    // Do not delete instructions that can have side effects which might cause
3446    // the unreachable to not be reachable; specifically, calls and volatile
3447    // operations may have this effect.
3448    if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
3449
3450    if (BBI->mayHaveSideEffects()) {
3451      if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
3452        if (SI->isVolatile())
3453          break;
3454      } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
3455        if (LI->isVolatile())
3456          break;
3457      } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
3458        if (RMWI->isVolatile())
3459          break;
3460      } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
3461        if (CXI->isVolatile())
3462          break;
3463      } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
3464                 !isa<LandingPadInst>(BBI)) {
3465        break;
3466      }
3467      // Note that deleting LandingPad's here is in fact okay, although it
3468      // involves a bit of subtle reasoning. If this inst is a LandingPad,
3469      // all the predecessors of this block will be the unwind edges of Invokes,
3470      // and we can therefore guarantee this block will be erased.
3471    }
3472
3473    // Delete this instruction (any uses are guaranteed to be dead)
3474    if (!BBI->use_empty())
3475      BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
3476    BBI->eraseFromParent();
3477    Changed = true;
3478  }
3479
3480  // If the unreachable instruction is the first in the block, take a gander
3481  // at all of the predecessors of this instruction, and simplify them.
3482  if (&BB->front() != UI) return Changed;
3483
3484  SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
3485  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
3486    TerminatorInst *TI = Preds[i]->getTerminator();
3487    IRBuilder<> Builder(TI);
3488    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
3489      if (BI->isUnconditional()) {
3490        if (BI->getSuccessor(0) == BB) {
3491          new UnreachableInst(TI->getContext(), TI);
3492          TI->eraseFromParent();
3493          Changed = true;
3494        }
3495      } else {
3496        if (BI->getSuccessor(0) == BB) {
3497          Builder.CreateBr(BI->getSuccessor(1));
3498          EraseTerminatorInstAndDCECond(BI);
3499        } else if (BI->getSuccessor(1) == BB) {
3500          Builder.CreateBr(BI->getSuccessor(0));
3501          EraseTerminatorInstAndDCECond(BI);
3502          Changed = true;
3503        }
3504      }
3505    } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
3506      for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
3507           i != e; ++i)
3508        if (i.getCaseSuccessor() == BB) {
3509          BB->removePredecessor(SI->getParent());
3510          SI->removeCase(i);
3511          --i; --e;
3512          Changed = true;
3513        }
3514    } else if ((isa<InvokeInst>(TI) &&
3515                cast<InvokeInst>(TI)->getUnwindDest() == BB) ||
3516               isa<CatchSwitchInst>(TI)) {
3517      removeUnwindEdge(TI->getParent());
3518      Changed = true;
3519    } else if (isa<CleanupReturnInst>(TI)) {
3520      new UnreachableInst(TI->getContext(), TI);
3521      TI->eraseFromParent();
3522      Changed = true;
3523    }
3524    // TODO: We can remove a catchswitch if all it's catchpads end in
3525    // unreachable.
3526  }
3527
3528  // If this block is now dead, remove it.
3529  if (pred_empty(BB) &&
3530      BB != &BB->getParent()->getEntryBlock()) {
3531    // We know there are no successors, so just nuke the block.
3532    BB->eraseFromParent();
3533    return true;
3534  }
3535
3536  return Changed;
3537}
3538
3539static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
3540  assert(Cases.size() >= 1);
3541
3542  array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
3543  for (size_t I = 1, E = Cases.size(); I != E; ++I) {
3544    if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
3545      return false;
3546  }
3547  return true;
3548}
3549
3550/// Turn a switch with two reachable destinations into an integer range
3551/// comparison and branch.
3552static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
3553  assert(SI->getNumCases() > 1 && "Degenerate switch?");
3554
3555  bool HasDefault =
3556      !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
3557
3558  // Partition the cases into two sets with different destinations.
3559  BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
3560  BasicBlock *DestB = nullptr;
3561  SmallVector <ConstantInt *, 16> CasesA;
3562  SmallVector <ConstantInt *, 16> CasesB;
3563
3564  for (SwitchInst::CaseIt I : SI->cases()) {
3565    BasicBlock *Dest = I.getCaseSuccessor();
3566    if (!DestA) DestA = Dest;
3567    if (Dest == DestA) {
3568      CasesA.push_back(I.getCaseValue());
3569      continue;
3570    }
3571    if (!DestB) DestB = Dest;
3572    if (Dest == DestB) {
3573      CasesB.push_back(I.getCaseValue());
3574      continue;
3575    }
3576    return false;  // More than two destinations.
3577  }
3578
3579  assert(DestA && DestB && "Single-destination switch should have been folded.");
3580  assert(DestA != DestB);
3581  assert(DestB != SI->getDefaultDest());
3582  assert(!CasesB.empty() && "There must be non-default cases.");
3583  assert(!CasesA.empty() || HasDefault);
3584
3585  // Figure out if one of the sets of cases form a contiguous range.
3586  SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
3587  BasicBlock *ContiguousDest = nullptr;
3588  BasicBlock *OtherDest = nullptr;
3589  if (!CasesA.empty() && CasesAreContiguous(CasesA)) {
3590    ContiguousCases = &CasesA;
3591    ContiguousDest = DestA;
3592    OtherDest = DestB;
3593  } else if (CasesAreContiguous(CasesB)) {
3594    ContiguousCases = &CasesB;
3595    ContiguousDest = DestB;
3596    OtherDest = DestA;
3597  } else
3598    return false;
3599
3600  // Start building the compare and branch.
3601
3602  Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
3603  Constant *NumCases = ConstantInt::get(Offset->getType(), ContiguousCases->size());
3604
3605  Value *Sub = SI->getCondition();
3606  if (!Offset->isNullValue())
3607    Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
3608
3609  Value *Cmp;
3610  // If NumCases overflowed, then all possible values jump to the successor.
3611  if (NumCases->isNullValue() && !ContiguousCases->empty())
3612    Cmp = ConstantInt::getTrue(SI->getContext());
3613  else
3614    Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
3615  BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
3616
3617  // Update weight for the newly-created conditional branch.
3618  if (HasBranchWeights(SI)) {
3619    SmallVector<uint64_t, 8> Weights;
3620    GetBranchWeights(SI, Weights);
3621    if (Weights.size() == 1 + SI->getNumCases()) {
3622      uint64_t TrueWeight = 0;
3623      uint64_t FalseWeight = 0;
3624      for (size_t I = 0, E = Weights.size(); I != E; ++I) {
3625        if (SI->getSuccessor(I) == ContiguousDest)
3626          TrueWeight += Weights[I];
3627        else
3628          FalseWeight += Weights[I];
3629      }
3630      while (TrueWeight > UINT32_MAX || FalseWeight > UINT32_MAX) {
3631        TrueWeight /= 2;
3632        FalseWeight /= 2;
3633      }
3634      NewBI->setMetadata(LLVMContext::MD_prof,
3635                         MDBuilder(SI->getContext()).createBranchWeights(
3636                             (uint32_t)TrueWeight, (uint32_t)FalseWeight));
3637    }
3638  }
3639
3640  // Prune obsolete incoming values off the successors' PHI nodes.
3641  for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
3642    unsigned PreviousEdges = ContiguousCases->size();
3643    if (ContiguousDest == SI->getDefaultDest()) ++PreviousEdges;
3644    for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
3645      cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
3646  }
3647  for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
3648    unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
3649    if (OtherDest == SI->getDefaultDest()) ++PreviousEdges;
3650    for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
3651      cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
3652  }
3653
3654  // Drop the switch.
3655  SI->eraseFromParent();
3656
3657  return true;
3658}
3659
3660/// Compute masked bits for the condition of a switch
3661/// and use it to remove dead cases.
3662static bool EliminateDeadSwitchCases(SwitchInst *SI, AssumptionCache *AC,
3663                                     const DataLayout &DL) {
3664  Value *Cond = SI->getCondition();
3665  unsigned Bits = Cond->getType()->getIntegerBitWidth();
3666  APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
3667  computeKnownBits(Cond, KnownZero, KnownOne, DL, 0, AC, SI);
3668
3669  // Gather dead cases.
3670  SmallVector<ConstantInt*, 8> DeadCases;
3671  for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3672    if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
3673        (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
3674      DeadCases.push_back(I.getCaseValue());
3675      DEBUG(dbgs() << "SimplifyCFG: switch case '"
3676                   << I.getCaseValue() << "' is dead.\n");
3677    }
3678  }
3679
3680  // If we can prove that the cases must cover all possible values, the
3681  // default destination becomes dead and we can remove it.  If we know some
3682  // of the bits in the value, we can use that to more precisely compute the
3683  // number of possible unique case values.
3684  bool HasDefault =
3685    !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
3686  const unsigned NumUnknownBits = Bits -
3687    (KnownZero.Or(KnownOne)).countPopulation();
3688  assert(NumUnknownBits <= Bits);
3689  if (HasDefault && DeadCases.empty() &&
3690      NumUnknownBits < 64 /* avoid overflow */ &&
3691      SI->getNumCases() == (1ULL << NumUnknownBits)) {
3692    DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n");
3693    BasicBlock *NewDefault = SplitBlockPredecessors(SI->getDefaultDest(),
3694                                                    SI->getParent(), "");
3695    SI->setDefaultDest(&*NewDefault);
3696    SplitBlock(&*NewDefault, &NewDefault->front());
3697    auto *OldTI = NewDefault->getTerminator();
3698    new UnreachableInst(SI->getContext(), OldTI);
3699    EraseTerminatorInstAndDCECond(OldTI);
3700    return true;
3701  }
3702
3703  SmallVector<uint64_t, 8> Weights;
3704  bool HasWeight = HasBranchWeights(SI);
3705  if (HasWeight) {
3706    GetBranchWeights(SI, Weights);
3707    HasWeight = (Weights.size() == 1 + SI->getNumCases());
3708  }
3709
3710  // Remove dead cases from the switch.
3711  for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
3712    SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
3713    assert(Case != SI->case_default() &&
3714           "Case was not found. Probably mistake in DeadCases forming.");
3715    if (HasWeight) {
3716      std::swap(Weights[Case.getCaseIndex()+1], Weights.back());
3717      Weights.pop_back();
3718    }
3719
3720    // Prune unused values from PHI nodes.
3721    Case.getCaseSuccessor()->removePredecessor(SI->getParent());
3722    SI->removeCase(Case);
3723  }
3724  if (HasWeight && Weights.size() >= 2) {
3725    SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3726    SI->setMetadata(LLVMContext::MD_prof,
3727                    MDBuilder(SI->getParent()->getContext()).
3728                    createBranchWeights(MDWeights));
3729  }
3730
3731  return !DeadCases.empty();
3732}
3733
3734/// If BB would be eligible for simplification by
3735/// TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
3736/// by an unconditional branch), look at the phi node for BB in the successor
3737/// block and see if the incoming value is equal to CaseValue. If so, return
3738/// the phi node, and set PhiIndex to BB's index in the phi node.
3739static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
3740                                              BasicBlock *BB,
3741                                              int *PhiIndex) {
3742  if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
3743    return nullptr; // BB must be empty to be a candidate for simplification.
3744  if (!BB->getSinglePredecessor())
3745    return nullptr; // BB must be dominated by the switch.
3746
3747  BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
3748  if (!Branch || !Branch->isUnconditional())
3749    return nullptr; // Terminator must be unconditional branch.
3750
3751  BasicBlock *Succ = Branch->getSuccessor(0);
3752
3753  BasicBlock::iterator I = Succ->begin();
3754  while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3755    int Idx = PHI->getBasicBlockIndex(BB);
3756    assert(Idx >= 0 && "PHI has no entry for predecessor?");
3757
3758    Value *InValue = PHI->getIncomingValue(Idx);
3759    if (InValue != CaseValue) continue;
3760
3761    *PhiIndex = Idx;
3762    return PHI;
3763  }
3764
3765  return nullptr;
3766}
3767
3768/// Try to forward the condition of a switch instruction to a phi node
3769/// dominated by the switch, if that would mean that some of the destination
3770/// blocks of the switch can be folded away.
3771/// Returns true if a change is made.
3772static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
3773  typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
3774  ForwardingNodesMap ForwardingNodes;
3775
3776  for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3777    ConstantInt *CaseValue = I.getCaseValue();
3778    BasicBlock *CaseDest = I.getCaseSuccessor();
3779
3780    int PhiIndex;
3781    PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
3782                                                 &PhiIndex);
3783    if (!PHI) continue;
3784
3785    ForwardingNodes[PHI].push_back(PhiIndex);
3786  }
3787
3788  bool Changed = false;
3789
3790  for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
3791       E = ForwardingNodes.end(); I != E; ++I) {
3792    PHINode *Phi = I->first;
3793    SmallVectorImpl<int> &Indexes = I->second;
3794
3795    if (Indexes.size() < 2) continue;
3796
3797    for (size_t I = 0, E = Indexes.size(); I != E; ++I)
3798      Phi->setIncomingValue(Indexes[I], SI->getCondition());
3799    Changed = true;
3800  }
3801
3802  return Changed;
3803}
3804
3805/// Return true if the backend will be able to handle
3806/// initializing an array of constants like C.
3807static bool ValidLookupTableConstant(Constant *C) {
3808  if (C->isThreadDependent())
3809    return false;
3810  if (C->isDLLImportDependent())
3811    return false;
3812
3813  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
3814    return CE->isGEPWithNoNotionalOverIndexing();
3815
3816  return isa<ConstantFP>(C) ||
3817      isa<ConstantInt>(C) ||
3818      isa<ConstantPointerNull>(C) ||
3819      isa<GlobalValue>(C) ||
3820      isa<UndefValue>(C);
3821}
3822
3823/// If V is a Constant, return it. Otherwise, try to look up
3824/// its constant value in ConstantPool, returning 0 if it's not there.
3825static Constant *LookupConstant(Value *V,
3826                         const SmallDenseMap<Value*, Constant*>& ConstantPool) {
3827  if (Constant *C = dyn_cast<Constant>(V))
3828    return C;
3829  return ConstantPool.lookup(V);
3830}
3831
3832/// Try to fold instruction I into a constant. This works for
3833/// simple instructions such as binary operations where both operands are
3834/// constant or can be replaced by constants from the ConstantPool. Returns the
3835/// resulting constant on success, 0 otherwise.
3836static Constant *
3837ConstantFold(Instruction *I, const DataLayout &DL,
3838             const SmallDenseMap<Value *, Constant *> &ConstantPool) {
3839  if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
3840    Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
3841    if (!A)
3842      return nullptr;
3843    if (A->isAllOnesValue())
3844      return LookupConstant(Select->getTrueValue(), ConstantPool);
3845    if (A->isNullValue())
3846      return LookupConstant(Select->getFalseValue(), ConstantPool);
3847    return nullptr;
3848  }
3849
3850  SmallVector<Constant *, 4> COps;
3851  for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) {
3852    if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool))
3853      COps.push_back(A);
3854    else
3855      return nullptr;
3856  }
3857
3858  if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
3859    return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0],
3860                                           COps[1], DL);
3861  }
3862
3863  return ConstantFoldInstOperands(I->getOpcode(), I->getType(), COps, DL);
3864}
3865
3866/// Try to determine the resulting constant values in phi nodes
3867/// at the common destination basic block, *CommonDest, for one of the case
3868/// destionations CaseDest corresponding to value CaseVal (0 for the default
3869/// case), of a switch instruction SI.
3870static bool
3871GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
3872               BasicBlock **CommonDest,
3873               SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
3874               const DataLayout &DL) {
3875  // The block from which we enter the common destination.
3876  BasicBlock *Pred = SI->getParent();
3877
3878  // If CaseDest is empty except for some side-effect free instructions through
3879  // which we can constant-propagate the CaseVal, continue to its successor.
3880  SmallDenseMap<Value*, Constant*> ConstantPool;
3881  ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
3882  for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E;
3883       ++I) {
3884    if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) {
3885      // If the terminator is a simple branch, continue to the next block.
3886      if (T->getNumSuccessors() != 1)
3887        return false;
3888      Pred = CaseDest;
3889      CaseDest = T->getSuccessor(0);
3890    } else if (isa<DbgInfoIntrinsic>(I)) {
3891      // Skip debug intrinsic.
3892      continue;
3893    } else if (Constant *C = ConstantFold(&*I, DL, ConstantPool)) {
3894      // Instruction is side-effect free and constant.
3895
3896      // If the instruction has uses outside this block or a phi node slot for
3897      // the block, it is not safe to bypass the instruction since it would then
3898      // no longer dominate all its uses.
3899      for (auto &Use : I->uses()) {
3900        User *User = Use.getUser();
3901        if (Instruction *I = dyn_cast<Instruction>(User))
3902          if (I->getParent() == CaseDest)
3903            continue;
3904        if (PHINode *Phi = dyn_cast<PHINode>(User))
3905          if (Phi->getIncomingBlock(Use) == CaseDest)
3906            continue;
3907        return false;
3908      }
3909
3910      ConstantPool.insert(std::make_pair(&*I, C));
3911    } else {
3912      break;
3913    }
3914  }
3915
3916  // If we did not have a CommonDest before, use the current one.
3917  if (!*CommonDest)
3918    *CommonDest = CaseDest;
3919  // If the destination isn't the common one, abort.
3920  if (CaseDest != *CommonDest)
3921    return false;
3922
3923  // Get the values for this case from phi nodes in the destination block.
3924  BasicBlock::iterator I = (*CommonDest)->begin();
3925  while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3926    int Idx = PHI->getBasicBlockIndex(Pred);
3927    if (Idx == -1)
3928      continue;
3929
3930    Constant *ConstVal = LookupConstant(PHI->getIncomingValue(Idx),
3931                                        ConstantPool);
3932    if (!ConstVal)
3933      return false;
3934
3935    // Be conservative about which kinds of constants we support.
3936    if (!ValidLookupTableConstant(ConstVal))
3937      return false;
3938
3939    Res.push_back(std::make_pair(PHI, ConstVal));
3940  }
3941
3942  return Res.size() > 0;
3943}
3944
3945// Helper function used to add CaseVal to the list of cases that generate
3946// Result.
3947static void MapCaseToResult(ConstantInt *CaseVal,
3948    SwitchCaseResultVectorTy &UniqueResults,
3949    Constant *Result) {
3950  for (auto &I : UniqueResults) {
3951    if (I.first == Result) {
3952      I.second.push_back(CaseVal);
3953      return;
3954    }
3955  }
3956  UniqueResults.push_back(std::make_pair(Result,
3957        SmallVector<ConstantInt*, 4>(1, CaseVal)));
3958}
3959
3960// Helper function that initializes a map containing
3961// results for the PHI node of the common destination block for a switch
3962// instruction. Returns false if multiple PHI nodes have been found or if
3963// there is not a common destination block for the switch.
3964static bool InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
3965                                  BasicBlock *&CommonDest,
3966                                  SwitchCaseResultVectorTy &UniqueResults,
3967                                  Constant *&DefaultResult,
3968                                  const DataLayout &DL) {
3969  for (auto &I : SI->cases()) {
3970    ConstantInt *CaseVal = I.getCaseValue();
3971
3972    // Resulting value at phi nodes for this case value.
3973    SwitchCaseResultsTy Results;
3974    if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
3975                        DL))
3976      return false;
3977
3978    // Only one value per case is permitted
3979    if (Results.size() > 1)
3980      return false;
3981    MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
3982
3983    // Check the PHI consistency.
3984    if (!PHI)
3985      PHI = Results[0].first;
3986    else if (PHI != Results[0].first)
3987      return false;
3988  }
3989  // Find the default result value.
3990  SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
3991  BasicBlock *DefaultDest = SI->getDefaultDest();
3992  GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
3993                 DL);
3994  // If the default value is not found abort unless the default destination
3995  // is unreachable.
3996  DefaultResult =
3997      DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
3998  if ((!DefaultResult &&
3999        !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
4000    return false;
4001
4002  return true;
4003}
4004
4005// Helper function that checks if it is possible to transform a switch with only
4006// two cases (or two cases + default) that produces a result into a select.
4007// Example:
4008// switch (a) {
4009//   case 10:                %0 = icmp eq i32 %a, 10
4010//     return 10;            %1 = select i1 %0, i32 10, i32 4
4011//   case 20:        ---->   %2 = icmp eq i32 %a, 20
4012//     return 2;             %3 = select i1 %2, i32 2, i32 %1
4013//   default:
4014//     return 4;
4015// }
4016static Value *
4017ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
4018                     Constant *DefaultResult, Value *Condition,
4019                     IRBuilder<> &Builder) {
4020  assert(ResultVector.size() == 2 &&
4021      "We should have exactly two unique results at this point");
4022  // If we are selecting between only two cases transform into a simple
4023  // select or a two-way select if default is possible.
4024  if (ResultVector[0].second.size() == 1 &&
4025      ResultVector[1].second.size() == 1) {
4026    ConstantInt *const FirstCase = ResultVector[0].second[0];
4027    ConstantInt *const SecondCase = ResultVector[1].second[0];
4028
4029    bool DefaultCanTrigger = DefaultResult;
4030    Value *SelectValue = ResultVector[1].first;
4031    if (DefaultCanTrigger) {
4032      Value *const ValueCompare =
4033          Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
4034      SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
4035                                         DefaultResult, "switch.select");
4036    }
4037    Value *const ValueCompare =
4038        Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
4039    return Builder.CreateSelect(ValueCompare, ResultVector[0].first, SelectValue,
4040                                "switch.select");
4041  }
4042
4043  return nullptr;
4044}
4045
4046// Helper function to cleanup a switch instruction that has been converted into
4047// a select, fixing up PHI nodes and basic blocks.
4048static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
4049                                              Value *SelectValue,
4050                                              IRBuilder<> &Builder) {
4051  BasicBlock *SelectBB = SI->getParent();
4052  while (PHI->getBasicBlockIndex(SelectBB) >= 0)
4053    PHI->removeIncomingValue(SelectBB);
4054  PHI->addIncoming(SelectValue, SelectBB);
4055
4056  Builder.CreateBr(PHI->getParent());
4057
4058  // Remove the switch.
4059  for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
4060    BasicBlock *Succ = SI->getSuccessor(i);
4061
4062    if (Succ == PHI->getParent())
4063      continue;
4064    Succ->removePredecessor(SelectBB);
4065  }
4066  SI->eraseFromParent();
4067}
4068
4069/// If the switch is only used to initialize one or more
4070/// phi nodes in a common successor block with only two different
4071/// constant values, replace the switch with select.
4072static bool SwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
4073                           AssumptionCache *AC, const DataLayout &DL) {
4074  Value *const Cond = SI->getCondition();
4075  PHINode *PHI = nullptr;
4076  BasicBlock *CommonDest = nullptr;
4077  Constant *DefaultResult;
4078  SwitchCaseResultVectorTy UniqueResults;
4079  // Collect all the cases that will deliver the same value from the switch.
4080  if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
4081                             DL))
4082    return false;
4083  // Selects choose between maximum two values.
4084  if (UniqueResults.size() != 2)
4085    return false;
4086  assert(PHI != nullptr && "PHI for value select not found");
4087
4088  Builder.SetInsertPoint(SI);
4089  Value *SelectValue = ConvertTwoCaseSwitch(
4090      UniqueResults,
4091      DefaultResult, Cond, Builder);
4092  if (SelectValue) {
4093    RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder);
4094    return true;
4095  }
4096  // The switch couldn't be converted into a select.
4097  return false;
4098}
4099
4100namespace {
4101  /// This class represents a lookup table that can be used to replace a switch.
4102  class SwitchLookupTable {
4103  public:
4104    /// Create a lookup table to use as a switch replacement with the contents
4105    /// of Values, using DefaultValue to fill any holes in the table.
4106    SwitchLookupTable(
4107        Module &M, uint64_t TableSize, ConstantInt *Offset,
4108        const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4109        Constant *DefaultValue, const DataLayout &DL);
4110
4111    /// Build instructions with Builder to retrieve the value at
4112    /// the position given by Index in the lookup table.
4113    Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
4114
4115    /// Return true if a table with TableSize elements of
4116    /// type ElementType would fit in a target-legal register.
4117    static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize,
4118                                   Type *ElementType);
4119
4120  private:
4121    // Depending on the contents of the table, it can be represented in
4122    // different ways.
4123    enum {
4124      // For tables where each element contains the same value, we just have to
4125      // store that single value and return it for each lookup.
4126      SingleValueKind,
4127
4128      // For tables where there is a linear relationship between table index
4129      // and values. We calculate the result with a simple multiplication
4130      // and addition instead of a table lookup.
4131      LinearMapKind,
4132
4133      // For small tables with integer elements, we can pack them into a bitmap
4134      // that fits into a target-legal register. Values are retrieved by
4135      // shift and mask operations.
4136      BitMapKind,
4137
4138      // The table is stored as an array of values. Values are retrieved by load
4139      // instructions from the table.
4140      ArrayKind
4141    } Kind;
4142
4143    // For SingleValueKind, this is the single value.
4144    Constant *SingleValue;
4145
4146    // For BitMapKind, this is the bitmap.
4147    ConstantInt *BitMap;
4148    IntegerType *BitMapElementTy;
4149
4150    // For LinearMapKind, these are the constants used to derive the value.
4151    ConstantInt *LinearOffset;
4152    ConstantInt *LinearMultiplier;
4153
4154    // For ArrayKind, this is the array.
4155    GlobalVariable *Array;
4156  };
4157}
4158
4159SwitchLookupTable::SwitchLookupTable(
4160    Module &M, uint64_t TableSize, ConstantInt *Offset,
4161    const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
4162    Constant *DefaultValue, const DataLayout &DL)
4163    : SingleValue(nullptr), BitMap(nullptr), BitMapElementTy(nullptr),
4164      LinearOffset(nullptr), LinearMultiplier(nullptr), Array(nullptr) {
4165  assert(Values.size() && "Can't build lookup table without values!");
4166  assert(TableSize >= Values.size() && "Can't fit values in table!");
4167
4168  // If all values in the table are equal, this is that value.
4169  SingleValue = Values.begin()->second;
4170
4171  Type *ValueType = Values.begin()->second->getType();
4172
4173  // Build up the table contents.
4174  SmallVector<Constant*, 64> TableContents(TableSize);
4175  for (size_t I = 0, E = Values.size(); I != E; ++I) {
4176    ConstantInt *CaseVal = Values[I].first;
4177    Constant *CaseRes = Values[I].second;
4178    assert(CaseRes->getType() == ValueType);
4179
4180    uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
4181                   .getLimitedValue();
4182    TableContents[Idx] = CaseRes;
4183
4184    if (CaseRes != SingleValue)
4185      SingleValue = nullptr;
4186  }
4187
4188  // Fill in any holes in the table with the default result.
4189  if (Values.size() < TableSize) {
4190    assert(DefaultValue &&
4191           "Need a default value to fill the lookup table holes.");
4192    assert(DefaultValue->getType() == ValueType);
4193    for (uint64_t I = 0; I < TableSize; ++I) {
4194      if (!TableContents[I])
4195        TableContents[I] = DefaultValue;
4196    }
4197
4198    if (DefaultValue != SingleValue)
4199      SingleValue = nullptr;
4200  }
4201
4202  // If each element in the table contains the same value, we only need to store
4203  // that single value.
4204  if (SingleValue) {
4205    Kind = SingleValueKind;
4206    return;
4207  }
4208
4209  // Check if we can derive the value with a linear transformation from the
4210  // table index.
4211  if (isa<IntegerType>(ValueType)) {
4212    bool LinearMappingPossible = true;
4213    APInt PrevVal;
4214    APInt DistToPrev;
4215    assert(TableSize >= 2 && "Should be a SingleValue table.");
4216    // Check if there is the same distance between two consecutive values.
4217    for (uint64_t I = 0; I < TableSize; ++I) {
4218      ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]);
4219      if (!ConstVal) {
4220        // This is an undef. We could deal with it, but undefs in lookup tables
4221        // are very seldom. It's probably not worth the additional complexity.
4222        LinearMappingPossible = false;
4223        break;
4224      }
4225      APInt Val = ConstVal->getValue();
4226      if (I != 0) {
4227        APInt Dist = Val - PrevVal;
4228        if (I == 1) {
4229          DistToPrev = Dist;
4230        } else if (Dist != DistToPrev) {
4231          LinearMappingPossible = false;
4232          break;
4233        }
4234      }
4235      PrevVal = Val;
4236    }
4237    if (LinearMappingPossible) {
4238      LinearOffset = cast<ConstantInt>(TableContents[0]);
4239      LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
4240      Kind = LinearMapKind;
4241      ++NumLinearMaps;
4242      return;
4243    }
4244  }
4245
4246  // If the type is integer and the table fits in a register, build a bitmap.
4247  if (WouldFitInRegister(DL, TableSize, ValueType)) {
4248    IntegerType *IT = cast<IntegerType>(ValueType);
4249    APInt TableInt(TableSize * IT->getBitWidth(), 0);
4250    for (uint64_t I = TableSize; I > 0; --I) {
4251      TableInt <<= IT->getBitWidth();
4252      // Insert values into the bitmap. Undef values are set to zero.
4253      if (!isa<UndefValue>(TableContents[I - 1])) {
4254        ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
4255        TableInt |= Val->getValue().zext(TableInt.getBitWidth());
4256      }
4257    }
4258    BitMap = ConstantInt::get(M.getContext(), TableInt);
4259    BitMapElementTy = IT;
4260    Kind = BitMapKind;
4261    ++NumBitMaps;
4262    return;
4263  }
4264
4265  // Store the table in an array.
4266  ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
4267  Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
4268
4269  Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
4270                             GlobalVariable::PrivateLinkage,
4271                             Initializer,
4272                             "switch.table");
4273  Array->setUnnamedAddr(true);
4274  Kind = ArrayKind;
4275}
4276
4277Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
4278  switch (Kind) {
4279    case SingleValueKind:
4280      return SingleValue;
4281    case LinearMapKind: {
4282      // Derive the result value from the input value.
4283      Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(),
4284                                            false, "switch.idx.cast");
4285      if (!LinearMultiplier->isOne())
4286        Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult");
4287      if (!LinearOffset->isZero())
4288        Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset");
4289      return Result;
4290    }
4291    case BitMapKind: {
4292      // Type of the bitmap (e.g. i59).
4293      IntegerType *MapTy = BitMap->getType();
4294
4295      // Cast Index to the same type as the bitmap.
4296      // Note: The Index is <= the number of elements in the table, so
4297      // truncating it to the width of the bitmask is safe.
4298      Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
4299
4300      // Multiply the shift amount by the element width.
4301      ShiftAmt = Builder.CreateMul(ShiftAmt,
4302                      ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
4303                                   "switch.shiftamt");
4304
4305      // Shift down.
4306      Value *DownShifted = Builder.CreateLShr(BitMap, ShiftAmt,
4307                                              "switch.downshift");
4308      // Mask off.
4309      return Builder.CreateTrunc(DownShifted, BitMapElementTy,
4310                                 "switch.masked");
4311    }
4312    case ArrayKind: {
4313      // Make sure the table index will not overflow when treated as signed.
4314      IntegerType *IT = cast<IntegerType>(Index->getType());
4315      uint64_t TableSize = Array->getInitializer()->getType()
4316                                ->getArrayNumElements();
4317      if (TableSize > (1ULL << (IT->getBitWidth() - 1)))
4318        Index = Builder.CreateZExt(Index,
4319                                   IntegerType::get(IT->getContext(),
4320                                                    IT->getBitWidth() + 1),
4321                                   "switch.tableidx.zext");
4322
4323      Value *GEPIndices[] = { Builder.getInt32(0), Index };
4324      Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array,
4325                                             GEPIndices, "switch.gep");
4326      return Builder.CreateLoad(GEP, "switch.load");
4327    }
4328  }
4329  llvm_unreachable("Unknown lookup table kind!");
4330}
4331
4332bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL,
4333                                           uint64_t TableSize,
4334                                           Type *ElementType) {
4335  auto *IT = dyn_cast<IntegerType>(ElementType);
4336  if (!IT)
4337    return false;
4338  // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
4339  // are <= 15, we could try to narrow the type.
4340
4341  // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
4342  if (TableSize >= UINT_MAX/IT->getBitWidth())
4343    return false;
4344  return DL.fitsInLegalInteger(TableSize * IT->getBitWidth());
4345}
4346
4347/// Determine whether a lookup table should be built for this switch, based on
4348/// the number of cases, size of the table, and the types of the results.
4349static bool
4350ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
4351                       const TargetTransformInfo &TTI, const DataLayout &DL,
4352                       const SmallDenseMap<PHINode *, Type *> &ResultTypes) {
4353  if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10)
4354    return false; // TableSize overflowed, or mul below might overflow.
4355
4356  bool AllTablesFitInRegister = true;
4357  bool HasIllegalType = false;
4358  for (const auto &I : ResultTypes) {
4359    Type *Ty = I.second;
4360
4361    // Saturate this flag to true.
4362    HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
4363
4364    // Saturate this flag to false.
4365    AllTablesFitInRegister = AllTablesFitInRegister &&
4366      SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty);
4367
4368    // If both flags saturate, we're done. NOTE: This *only* works with
4369    // saturating flags, and all flags have to saturate first due to the
4370    // non-deterministic behavior of iterating over a dense map.
4371    if (HasIllegalType && !AllTablesFitInRegister)
4372      break;
4373  }
4374
4375  // If each table would fit in a register, we should build it anyway.
4376  if (AllTablesFitInRegister)
4377    return true;
4378
4379  // Don't build a table that doesn't fit in-register if it has illegal types.
4380  if (HasIllegalType)
4381    return false;
4382
4383  // The table density should be at least 40%. This is the same criterion as for
4384  // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
4385  // FIXME: Find the best cut-off.
4386  return SI->getNumCases() * 10 >= TableSize * 4;
4387}
4388
4389/// Try to reuse the switch table index compare. Following pattern:
4390/// \code
4391///     if (idx < tablesize)
4392///        r = table[idx]; // table does not contain default_value
4393///     else
4394///        r = default_value;
4395///     if (r != default_value)
4396///        ...
4397/// \endcode
4398/// Is optimized to:
4399/// \code
4400///     cond = idx < tablesize;
4401///     if (cond)
4402///        r = table[idx];
4403///     else
4404///        r = default_value;
4405///     if (cond)
4406///        ...
4407/// \endcode
4408/// Jump threading will then eliminate the second if(cond).
4409static void reuseTableCompare(User *PhiUser, BasicBlock *PhiBlock,
4410          BranchInst *RangeCheckBranch, Constant *DefaultValue,
4411          const SmallVectorImpl<std::pair<ConstantInt*, Constant*> >& Values) {
4412
4413  ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser);
4414  if (!CmpInst)
4415    return;
4416
4417  // We require that the compare is in the same block as the phi so that jump
4418  // threading can do its work afterwards.
4419  if (CmpInst->getParent() != PhiBlock)
4420    return;
4421
4422  Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1));
4423  if (!CmpOp1)
4424    return;
4425
4426  Value *RangeCmp = RangeCheckBranch->getCondition();
4427  Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType());
4428  Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType());
4429
4430  // Check if the compare with the default value is constant true or false.
4431  Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
4432                                                 DefaultValue, CmpOp1, true);
4433  if (DefaultConst != TrueConst && DefaultConst != FalseConst)
4434    return;
4435
4436  // Check if the compare with the case values is distinct from the default
4437  // compare result.
4438  for (auto ValuePair : Values) {
4439    Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
4440                              ValuePair.second, CmpOp1, true);
4441    if (!CaseConst || CaseConst == DefaultConst)
4442      return;
4443    assert((CaseConst == TrueConst || CaseConst == FalseConst) &&
4444           "Expect true or false as compare result.");
4445  }
4446
4447  // Check if the branch instruction dominates the phi node. It's a simple
4448  // dominance check, but sufficient for our needs.
4449  // Although this check is invariant in the calling loops, it's better to do it
4450  // at this late stage. Practically we do it at most once for a switch.
4451  BasicBlock *BranchBlock = RangeCheckBranch->getParent();
4452  for (auto PI = pred_begin(PhiBlock), E = pred_end(PhiBlock); PI != E; ++PI) {
4453    BasicBlock *Pred = *PI;
4454    if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock)
4455      return;
4456  }
4457
4458  if (DefaultConst == FalseConst) {
4459    // The compare yields the same result. We can replace it.
4460    CmpInst->replaceAllUsesWith(RangeCmp);
4461    ++NumTableCmpReuses;
4462  } else {
4463    // The compare yields the same result, just inverted. We can replace it.
4464    Value *InvertedTableCmp = BinaryOperator::CreateXor(RangeCmp,
4465                ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp",
4466                RangeCheckBranch);
4467    CmpInst->replaceAllUsesWith(InvertedTableCmp);
4468    ++NumTableCmpReuses;
4469  }
4470}
4471
4472/// If the switch is only used to initialize one or more phi nodes in a common
4473/// successor block with different constant values, replace the switch with
4474/// lookup tables.
4475static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
4476                                const DataLayout &DL,
4477                                const TargetTransformInfo &TTI) {
4478  assert(SI->getNumCases() > 1 && "Degenerate switch?");
4479
4480  // Only build lookup table when we have a target that supports it.
4481  if (!TTI.shouldBuildLookupTables())
4482    return false;
4483
4484  // FIXME: If the switch is too sparse for a lookup table, perhaps we could
4485  // split off a dense part and build a lookup table for that.
4486
4487  // FIXME: This creates arrays of GEPs to constant strings, which means each
4488  // GEP needs a runtime relocation in PIC code. We should just build one big
4489  // string and lookup indices into that.
4490
4491  // Ignore switches with less than three cases. Lookup tables will not make them
4492  // faster, so we don't analyze them.
4493  if (SI->getNumCases() < 3)
4494    return false;
4495
4496  // Figure out the corresponding result for each case value and phi node in the
4497  // common destination, as well as the min and max case values.
4498  assert(SI->case_begin() != SI->case_end());
4499  SwitchInst::CaseIt CI = SI->case_begin();
4500  ConstantInt *MinCaseVal = CI.getCaseValue();
4501  ConstantInt *MaxCaseVal = CI.getCaseValue();
4502
4503  BasicBlock *CommonDest = nullptr;
4504  typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy;
4505  SmallDenseMap<PHINode*, ResultListTy> ResultLists;
4506  SmallDenseMap<PHINode*, Constant*> DefaultResults;
4507  SmallDenseMap<PHINode*, Type*> ResultTypes;
4508  SmallVector<PHINode*, 4> PHIs;
4509
4510  for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
4511    ConstantInt *CaseVal = CI.getCaseValue();
4512    if (CaseVal->getValue().slt(MinCaseVal->getValue()))
4513      MinCaseVal = CaseVal;
4514    if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
4515      MaxCaseVal = CaseVal;
4516
4517    // Resulting value at phi nodes for this case value.
4518    typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy;
4519    ResultsTy Results;
4520    if (!GetCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest,
4521                        Results, DL))
4522      return false;
4523
4524    // Append the result from this case to the list for each phi.
4525    for (const auto &I : Results) {
4526      PHINode *PHI = I.first;
4527      Constant *Value = I.second;
4528      if (!ResultLists.count(PHI))
4529        PHIs.push_back(PHI);
4530      ResultLists[PHI].push_back(std::make_pair(CaseVal, Value));
4531    }
4532  }
4533
4534  // Keep track of the result types.
4535  for (PHINode *PHI : PHIs) {
4536    ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
4537  }
4538
4539  uint64_t NumResults = ResultLists[PHIs[0]].size();
4540  APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
4541  uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
4542  bool TableHasHoles = (NumResults < TableSize);
4543
4544  // If the table has holes, we need a constant result for the default case
4545  // or a bitmask that fits in a register.
4546  SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
4547  bool HasDefaultResults = GetCaseResults(SI, nullptr, SI->getDefaultDest(),
4548                                          &CommonDest, DefaultResultsList, DL);
4549
4550  bool NeedMask = (TableHasHoles && !HasDefaultResults);
4551  if (NeedMask) {
4552    // As an extra penalty for the validity test we require more cases.
4553    if (SI->getNumCases() < 4)  // FIXME: Find best threshold value (benchmark).
4554      return false;
4555    if (!DL.fitsInLegalInteger(TableSize))
4556      return false;
4557  }
4558
4559  for (const auto &I : DefaultResultsList) {
4560    PHINode *PHI = I.first;
4561    Constant *Result = I.second;
4562    DefaultResults[PHI] = Result;
4563  }
4564
4565  if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
4566    return false;
4567
4568  // Create the BB that does the lookups.
4569  Module &Mod = *CommonDest->getParent()->getParent();
4570  BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
4571                                            "switch.lookup",
4572                                            CommonDest->getParent(),
4573                                            CommonDest);
4574
4575  // Compute the table index value.
4576  Builder.SetInsertPoint(SI);
4577  Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
4578                                        "switch.tableidx");
4579
4580  // Compute the maximum table size representable by the integer type we are
4581  // switching upon.
4582  unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
4583  uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX : 1ULL << CaseSize;
4584  assert(MaxTableSize >= TableSize &&
4585         "It is impossible for a switch to have more entries than the max "
4586         "representable value of its input integer type's size.");
4587
4588  // If the default destination is unreachable, or if the lookup table covers
4589  // all values of the conditional variable, branch directly to the lookup table
4590  // BB. Otherwise, check that the condition is within the case range.
4591  const bool DefaultIsReachable =
4592      !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4593  const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
4594  BranchInst *RangeCheckBranch = nullptr;
4595
4596  if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
4597    Builder.CreateBr(LookupBB);
4598    // Note: We call removeProdecessor later since we need to be able to get the
4599    // PHI value for the default case in case we're using a bit mask.
4600  } else {
4601    Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
4602                                       MinCaseVal->getType(), TableSize));
4603    RangeCheckBranch = Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
4604  }
4605
4606  // Populate the BB that does the lookups.
4607  Builder.SetInsertPoint(LookupBB);
4608
4609  if (NeedMask) {
4610    // Before doing the lookup we do the hole check.
4611    // The LookupBB is therefore re-purposed to do the hole check
4612    // and we create a new LookupBB.
4613    BasicBlock *MaskBB = LookupBB;
4614    MaskBB->setName("switch.hole_check");
4615    LookupBB = BasicBlock::Create(Mod.getContext(),
4616                                  "switch.lookup",
4617                                  CommonDest->getParent(),
4618                                  CommonDest);
4619
4620    // Make the mask's bitwidth at least 8bit and a power-of-2 to avoid
4621    // unnecessary illegal types.
4622    uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
4623    APInt MaskInt(TableSizePowOf2, 0);
4624    APInt One(TableSizePowOf2, 1);
4625    // Build bitmask; fill in a 1 bit for every case.
4626    const ResultListTy &ResultList = ResultLists[PHIs[0]];
4627    for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
4628      uint64_t Idx = (ResultList[I].first->getValue() -
4629                      MinCaseVal->getValue()).getLimitedValue();
4630      MaskInt |= One << Idx;
4631    }
4632    ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt);
4633
4634    // Get the TableIndex'th bit of the bitmask.
4635    // If this bit is 0 (meaning hole) jump to the default destination,
4636    // else continue with table lookup.
4637    IntegerType *MapTy = TableMask->getType();
4638    Value *MaskIndex = Builder.CreateZExtOrTrunc(TableIndex, MapTy,
4639                                                 "switch.maskindex");
4640    Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex,
4641                                        "switch.shifted");
4642    Value *LoBit = Builder.CreateTrunc(Shifted,
4643                                       Type::getInt1Ty(Mod.getContext()),
4644                                       "switch.lobit");
4645    Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest());
4646
4647    Builder.SetInsertPoint(LookupBB);
4648    AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent());
4649  }
4650
4651  if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
4652    // We cached PHINodes in PHIs, to avoid accessing deleted PHINodes later,
4653    // do not delete PHINodes here.
4654    SI->getDefaultDest()->removePredecessor(SI->getParent(),
4655                                            /*DontDeleteUselessPHIs=*/true);
4656  }
4657
4658  bool ReturnedEarly = false;
4659  for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
4660    PHINode *PHI = PHIs[I];
4661    const ResultListTy &ResultList = ResultLists[PHI];
4662
4663    // If using a bitmask, use any value to fill the lookup table holes.
4664    Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI];
4665    SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL);
4666
4667    Value *Result = Table.BuildLookup(TableIndex, Builder);
4668
4669    // If the result is used to return immediately from the function, we want to
4670    // do that right here.
4671    if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->user_begin()) &&
4672        PHI->user_back() == CommonDest->getFirstNonPHIOrDbg()) {
4673      Builder.CreateRet(Result);
4674      ReturnedEarly = true;
4675      break;
4676    }
4677
4678    // Do a small peephole optimization: re-use the switch table compare if
4679    // possible.
4680    if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) {
4681      BasicBlock *PhiBlock = PHI->getParent();
4682      // Search for compare instructions which use the phi.
4683      for (auto *User : PHI->users()) {
4684        reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList);
4685      }
4686    }
4687
4688    PHI->addIncoming(Result, LookupBB);
4689  }
4690
4691  if (!ReturnedEarly)
4692    Builder.CreateBr(CommonDest);
4693
4694  // Remove the switch.
4695  for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
4696    BasicBlock *Succ = SI->getSuccessor(i);
4697
4698    if (Succ == SI->getDefaultDest())
4699      continue;
4700    Succ->removePredecessor(SI->getParent());
4701  }
4702  SI->eraseFromParent();
4703
4704  ++NumLookupTables;
4705  if (NeedMask)
4706    ++NumLookupTablesHoles;
4707  return true;
4708}
4709
4710bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
4711  BasicBlock *BB = SI->getParent();
4712
4713  if (isValueEqualityComparison(SI)) {
4714    // If we only have one predecessor, and if it is a branch on this value,
4715    // see if that predecessor totally determines the outcome of this switch.
4716    if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
4717      if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
4718        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4719
4720    Value *Cond = SI->getCondition();
4721    if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
4722      if (SimplifySwitchOnSelect(SI, Select))
4723        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4724
4725    // If the block only contains the switch, see if we can fold the block
4726    // away into any preds.
4727    BasicBlock::iterator BBI = BB->begin();
4728    // Ignore dbg intrinsics.
4729    while (isa<DbgInfoIntrinsic>(BBI))
4730      ++BBI;
4731    if (SI == &*BBI)
4732      if (FoldValueComparisonIntoPredecessors(SI, Builder))
4733        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4734  }
4735
4736  // Try to transform the switch into an icmp and a branch.
4737  if (TurnSwitchRangeIntoICmp(SI, Builder))
4738    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4739
4740  // Remove unreachable cases.
4741  if (EliminateDeadSwitchCases(SI, AC, DL))
4742    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4743
4744  if (SwitchToSelect(SI, Builder, AC, DL))
4745    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4746
4747  if (ForwardSwitchConditionToPHI(SI))
4748    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4749
4750  if (SwitchToLookupTable(SI, Builder, DL, TTI))
4751    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4752
4753  return false;
4754}
4755
4756bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
4757  BasicBlock *BB = IBI->getParent();
4758  bool Changed = false;
4759
4760  // Eliminate redundant destinations.
4761  SmallPtrSet<Value *, 8> Succs;
4762  for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
4763    BasicBlock *Dest = IBI->getDestination(i);
4764    if (!Dest->hasAddressTaken() || !Succs.insert(Dest).second) {
4765      Dest->removePredecessor(BB);
4766      IBI->removeDestination(i);
4767      --i; --e;
4768      Changed = true;
4769    }
4770  }
4771
4772  if (IBI->getNumDestinations() == 0) {
4773    // If the indirectbr has no successors, change it to unreachable.
4774    new UnreachableInst(IBI->getContext(), IBI);
4775    EraseTerminatorInstAndDCECond(IBI);
4776    return true;
4777  }
4778
4779  if (IBI->getNumDestinations() == 1) {
4780    // If the indirectbr has one successor, change it to a direct branch.
4781    BranchInst::Create(IBI->getDestination(0), IBI);
4782    EraseTerminatorInstAndDCECond(IBI);
4783    return true;
4784  }
4785
4786  if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
4787    if (SimplifyIndirectBrOnSelect(IBI, SI))
4788      return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4789  }
4790  return Changed;
4791}
4792
4793/// Given an block with only a single landing pad and a unconditional branch
4794/// try to find another basic block which this one can be merged with.  This
4795/// handles cases where we have multiple invokes with unique landing pads, but
4796/// a shared handler.
4797///
4798/// We specifically choose to not worry about merging non-empty blocks
4799/// here.  That is a PRE/scheduling problem and is best solved elsewhere.  In
4800/// practice, the optimizer produces empty landing pad blocks quite frequently
4801/// when dealing with exception dense code.  (see: instcombine, gvn, if-else
4802/// sinking in this file)
4803///
4804/// This is primarily a code size optimization.  We need to avoid performing
4805/// any transform which might inhibit optimization (such as our ability to
4806/// specialize a particular handler via tail commoning).  We do this by not
4807/// merging any blocks which require us to introduce a phi.  Since the same
4808/// values are flowing through both blocks, we don't loose any ability to
4809/// specialize.  If anything, we make such specialization more likely.
4810///
4811/// TODO - This transformation could remove entries from a phi in the target
4812/// block when the inputs in the phi are the same for the two blocks being
4813/// merged.  In some cases, this could result in removal of the PHI entirely.
4814static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
4815                                 BasicBlock *BB) {
4816  auto Succ = BB->getUniqueSuccessor();
4817  assert(Succ);
4818  // If there's a phi in the successor block, we'd likely have to introduce
4819  // a phi into the merged landing pad block.
4820  if (isa<PHINode>(*Succ->begin()))
4821    return false;
4822
4823  for (BasicBlock *OtherPred : predecessors(Succ)) {
4824    if (BB == OtherPred)
4825      continue;
4826    BasicBlock::iterator I = OtherPred->begin();
4827    LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I);
4828    if (!LPad2 || !LPad2->isIdenticalTo(LPad))
4829      continue;
4830    for (++I; isa<DbgInfoIntrinsic>(I); ++I) {}
4831    BranchInst *BI2 = dyn_cast<BranchInst>(I);
4832    if (!BI2 || !BI2->isIdenticalTo(BI))
4833      continue;
4834
4835    // We've found an identical block.  Update our predeccessors to take that
4836    // path instead and make ourselves dead.
4837    SmallSet<BasicBlock *, 16> Preds;
4838    Preds.insert(pred_begin(BB), pred_end(BB));
4839    for (BasicBlock *Pred : Preds) {
4840      InvokeInst *II = cast<InvokeInst>(Pred->getTerminator());
4841      assert(II->getNormalDest() != BB &&
4842             II->getUnwindDest() == BB && "unexpected successor");
4843      II->setUnwindDest(OtherPred);
4844    }
4845
4846    // The debug info in OtherPred doesn't cover the merged control flow that
4847    // used to go through BB.  We need to delete it or update it.
4848    for (auto I = OtherPred->begin(), E = OtherPred->end();
4849         I != E;) {
4850      Instruction &Inst = *I; I++;
4851      if (isa<DbgInfoIntrinsic>(Inst))
4852        Inst.eraseFromParent();
4853    }
4854
4855    SmallSet<BasicBlock *, 16> Succs;
4856    Succs.insert(succ_begin(BB), succ_end(BB));
4857    for (BasicBlock *Succ : Succs) {
4858      Succ->removePredecessor(BB);
4859    }
4860
4861    IRBuilder<> Builder(BI);
4862    Builder.CreateUnreachable();
4863    BI->eraseFromParent();
4864    return true;
4865  }
4866  return false;
4867}
4868
4869bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
4870  BasicBlock *BB = BI->getParent();
4871
4872  if (SinkCommon && SinkThenElseCodeToEnd(BI))
4873    return true;
4874
4875  // If the Terminator is the only non-phi instruction, simplify the block.
4876  BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
4877  if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
4878      TryToSimplifyUncondBranchFromEmptyBlock(BB))
4879    return true;
4880
4881  // If the only instruction in the block is a seteq/setne comparison
4882  // against a constant, try to simplify the block.
4883  if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
4884    if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
4885      for (++I; isa<DbgInfoIntrinsic>(I); ++I)
4886        ;
4887      if (I->isTerminator() &&
4888          TryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, DL, TTI,
4889                                                BonusInstThreshold, AC))
4890        return true;
4891    }
4892
4893  // See if we can merge an empty landing pad block with another which is
4894  // equivalent.
4895  if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) {
4896    for (++I; isa<DbgInfoIntrinsic>(I); ++I) {}
4897    if (I->isTerminator() &&
4898        TryToMergeLandingPad(LPad, BI, BB))
4899      return true;
4900  }
4901
4902  // If this basic block is ONLY a compare and a branch, and if a predecessor
4903  // branches to us and our successor, fold the comparison into the
4904  // predecessor and use logical operations to update the incoming value
4905  // for PHI nodes in common successor.
4906  if (FoldBranchToCommonDest(BI, BonusInstThreshold))
4907    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4908  return false;
4909}
4910
4911static BasicBlock *allPredecessorsComeFromSameSource(BasicBlock *BB) {
4912  BasicBlock *PredPred = nullptr;
4913  for (auto *P : predecessors(BB)) {
4914    BasicBlock *PPred = P->getSinglePredecessor();
4915    if (!PPred || (PredPred && PredPred != PPred))
4916      return nullptr;
4917    PredPred = PPred;
4918  }
4919  return PredPred;
4920}
4921
4922bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
4923  BasicBlock *BB = BI->getParent();
4924
4925  // Conditional branch
4926  if (isValueEqualityComparison(BI)) {
4927    // If we only have one predecessor, and if it is a branch on this value,
4928    // see if that predecessor totally determines the outcome of this
4929    // switch.
4930    if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
4931      if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
4932        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4933
4934    // This block must be empty, except for the setcond inst, if it exists.
4935    // Ignore dbg intrinsics.
4936    BasicBlock::iterator I = BB->begin();
4937    // Ignore dbg intrinsics.
4938    while (isa<DbgInfoIntrinsic>(I))
4939      ++I;
4940    if (&*I == BI) {
4941      if (FoldValueComparisonIntoPredecessors(BI, Builder))
4942        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4943    } else if (&*I == cast<Instruction>(BI->getCondition())){
4944      ++I;
4945      // Ignore dbg intrinsics.
4946      while (isa<DbgInfoIntrinsic>(I))
4947        ++I;
4948      if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
4949        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4950    }
4951  }
4952
4953  // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
4954  if (SimplifyBranchOnICmpChain(BI, Builder, DL))
4955    return true;
4956
4957  // If this basic block is ONLY a compare and a branch, and if a predecessor
4958  // branches to us and one of our successors, fold the comparison into the
4959  // predecessor and use logical operations to pick the right destination.
4960  if (FoldBranchToCommonDest(BI, BonusInstThreshold))
4961    return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4962
4963  // We have a conditional branch to two blocks that are only reachable
4964  // from BI.  We know that the condbr dominates the two blocks, so see if
4965  // there is any identical code in the "then" and "else" blocks.  If so, we
4966  // can hoist it up to the branching block.
4967  if (BI->getSuccessor(0)->getSinglePredecessor()) {
4968    if (BI->getSuccessor(1)->getSinglePredecessor()) {
4969      if (HoistThenElseCodeToIf(BI, TTI))
4970        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4971    } else {
4972      // If Successor #1 has multiple preds, we may be able to conditionally
4973      // execute Successor #0 if it branches to Successor #1.
4974      TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
4975      if (Succ0TI->getNumSuccessors() == 1 &&
4976          Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
4977        if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI))
4978          return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4979    }
4980  } else if (BI->getSuccessor(1)->getSinglePredecessor()) {
4981    // If Successor #0 has multiple preds, we may be able to conditionally
4982    // execute Successor #1 if it branches to Successor #0.
4983    TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
4984    if (Succ1TI->getNumSuccessors() == 1 &&
4985        Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
4986      if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI))
4987        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4988  }
4989
4990  // If this is a branch on a phi node in the current block, thread control
4991  // through this block if any PHI node entries are constants.
4992  if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
4993    if (PN->getParent() == BI->getParent())
4994      if (FoldCondBranchOnPHI(BI, DL))
4995        return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
4996
4997  // Scan predecessor blocks for conditional branches.
4998  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
4999    if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
5000      if (PBI != BI && PBI->isConditional())
5001        if (SimplifyCondBranchToCondBranch(PBI, BI, DL))
5002          return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5003
5004  // Look for diamond patterns.
5005  if (MergeCondStores)
5006    if (BasicBlock *PrevBB = allPredecessorsComeFromSameSource(BB))
5007      if (BranchInst *PBI = dyn_cast<BranchInst>(PrevBB->getTerminator()))
5008        if (PBI != BI && PBI->isConditional())
5009          if (mergeConditionalStores(PBI, BI))
5010            return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
5011
5012  return false;
5013}
5014
5015/// Check if passing a value to an instruction will cause undefined behavior.
5016static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
5017  Constant *C = dyn_cast<Constant>(V);
5018  if (!C)
5019    return false;
5020
5021  if (I->use_empty())
5022    return false;
5023
5024  if (C->isNullValue()) {
5025    // Only look at the first use, avoid hurting compile time with long uselists
5026    User *Use = *I->user_begin();
5027
5028    // Now make sure that there are no instructions in between that can alter
5029    // control flow (eg. calls)
5030    for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
5031      if (i == I->getParent()->end() || i->mayHaveSideEffects())
5032        return false;
5033
5034    // Look through GEPs. A load from a GEP derived from NULL is still undefined
5035    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
5036      if (GEP->getPointerOperand() == I)
5037        return passingValueIsAlwaysUndefined(V, GEP);
5038
5039    // Look through bitcasts.
5040    if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
5041      return passingValueIsAlwaysUndefined(V, BC);
5042
5043    // Load from null is undefined.
5044    if (LoadInst *LI = dyn_cast<LoadInst>(Use))
5045      if (!LI->isVolatile())
5046        return LI->getPointerAddressSpace() == 0;
5047
5048    // Store to null is undefined.
5049    if (StoreInst *SI = dyn_cast<StoreInst>(Use))
5050      if (!SI->isVolatile())
5051        return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
5052  }
5053  return false;
5054}
5055
5056/// If BB has an incoming value that will always trigger undefined behavior
5057/// (eg. null pointer dereference), remove the branch leading here.
5058static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
5059  for (BasicBlock::iterator i = BB->begin();
5060       PHINode *PHI = dyn_cast<PHINode>(i); ++i)
5061    for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
5062      if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
5063        TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
5064        IRBuilder<> Builder(T);
5065        if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
5066          BB->removePredecessor(PHI->getIncomingBlock(i));
5067          // Turn uncoditional branches into unreachables and remove the dead
5068          // destination from conditional branches.
5069          if (BI->isUnconditional())
5070            Builder.CreateUnreachable();
5071          else
5072            Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
5073                                                         BI->getSuccessor(0));
5074          BI->eraseFromParent();
5075          return true;
5076        }
5077        // TODO: SwitchInst.
5078      }
5079
5080  return false;
5081}
5082
5083bool SimplifyCFGOpt::run(BasicBlock *BB) {
5084  bool Changed = false;
5085
5086  assert(BB && BB->getParent() && "Block not embedded in function!");
5087  assert(BB->getTerminator() && "Degenerate basic block encountered!");
5088
5089  // Remove basic blocks that have no predecessors (except the entry block)...
5090  // or that just have themself as a predecessor.  These are unreachable.
5091  if ((pred_empty(BB) &&
5092       BB != &BB->getParent()->getEntryBlock()) ||
5093      BB->getSinglePredecessor() == BB) {
5094    DEBUG(dbgs() << "Removing BB: \n" << *BB);
5095    DeleteDeadBlock(BB);
5096    return true;
5097  }
5098
5099  // Check to see if we can constant propagate this terminator instruction
5100  // away...
5101  Changed |= ConstantFoldTerminator(BB, true);
5102
5103  // Check for and eliminate duplicate PHI nodes in this block.
5104  Changed |= EliminateDuplicatePHINodes(BB);
5105
5106  // Check for and remove branches that will always cause undefined behavior.
5107  Changed |= removeUndefIntroducingPredecessor(BB);
5108
5109  // Merge basic blocks into their predecessor if there is only one distinct
5110  // pred, and if there is only one distinct successor of the predecessor, and
5111  // if there are no PHI nodes.
5112  //
5113  if (MergeBlockIntoPredecessor(BB))
5114    return true;
5115
5116  IRBuilder<> Builder(BB);
5117
5118  // If there is a trivial two-entry PHI node in this basic block, and we can
5119  // eliminate it, do so now.
5120  if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
5121    if (PN->getNumIncomingValues() == 2)
5122      Changed |= FoldTwoEntryPHINode(PN, TTI, DL);
5123
5124  Builder.SetInsertPoint(BB->getTerminator());
5125  if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
5126    if (BI->isUnconditional()) {
5127      if (SimplifyUncondBranch(BI, Builder)) return true;
5128    } else {
5129      if (SimplifyCondBranch(BI, Builder)) return true;
5130    }
5131  } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
5132    if (SimplifyReturn(RI, Builder)) return true;
5133  } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
5134    if (SimplifyResume(RI, Builder)) return true;
5135  } else if (CleanupReturnInst *RI =
5136               dyn_cast<CleanupReturnInst>(BB->getTerminator())) {
5137    if (SimplifyCleanupReturn(RI)) return true;
5138  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
5139    if (SimplifySwitch(SI, Builder)) return true;
5140  } else if (UnreachableInst *UI =
5141               dyn_cast<UnreachableInst>(BB->getTerminator())) {
5142    if (SimplifyUnreachable(UI)) return true;
5143  } else if (IndirectBrInst *IBI =
5144               dyn_cast<IndirectBrInst>(BB->getTerminator())) {
5145    if (SimplifyIndirectBr(IBI)) return true;
5146  }
5147
5148  return Changed;
5149}
5150
5151/// This function is used to do simplification of a CFG.
5152/// For example, it adjusts branches to branches to eliminate the extra hop,
5153/// eliminates unreachable basic blocks, and does other "peephole" optimization
5154/// of the CFG.  It returns true if a modification was made.
5155///
5156bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
5157                       unsigned BonusInstThreshold, AssumptionCache *AC) {
5158  return SimplifyCFGOpt(TTI, BB->getModule()->getDataLayout(),
5159                        BonusInstThreshold, AC).run(BB);
5160}
5161