1//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
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// This family of functions perform manipulations on basic blocks, and
11// instructions contained within basic blocks.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Transforms/Utils/BasicBlockUtils.h"
16#include "llvm/Analysis/AliasAnalysis.h"
17#include "llvm/Analysis/CFG.h"
18#include "llvm/Analysis/LoopInfo.h"
19#include "llvm/Analysis/MemoryDependenceAnalysis.h"
20#include "llvm/IR/Constant.h"
21#include "llvm/IR/DataLayout.h"
22#include "llvm/IR/Dominators.h"
23#include "llvm/IR/Function.h"
24#include "llvm/IR/Instructions.h"
25#include "llvm/IR/IntrinsicInst.h"
26#include "llvm/IR/Type.h"
27#include "llvm/IR/ValueHandle.h"
28#include "llvm/Support/ErrorHandling.h"
29#include "llvm/Transforms/Scalar.h"
30#include "llvm/Transforms/Utils/Local.h"
31#include <algorithm>
32using namespace llvm;
33
34void llvm::DeleteDeadBlock(BasicBlock *BB) {
35  assert((pred_begin(BB) == pred_end(BB) ||
36         // Can delete self loop.
37         BB->getSinglePredecessor() == BB) && "Block is not dead!");
38  TerminatorInst *BBTerm = BB->getTerminator();
39
40  // Loop through all of our successors and make sure they know that one
41  // of their predecessors is going away.
42  for (BasicBlock *Succ : BBTerm->successors())
43    Succ->removePredecessor(BB);
44
45  // Zap all the instructions in the block.
46  while (!BB->empty()) {
47    Instruction &I = BB->back();
48    // If this instruction is used, replace uses with an arbitrary value.
49    // Because control flow can't get here, we don't care what we replace the
50    // value with.  Note that since this block is unreachable, and all values
51    // contained within it must dominate their uses, that all uses will
52    // eventually be removed (they are themselves dead).
53    if (!I.use_empty())
54      I.replaceAllUsesWith(UndefValue::get(I.getType()));
55    BB->getInstList().pop_back();
56  }
57
58  // Zap the block!
59  BB->eraseFromParent();
60}
61
62void llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
63                                   MemoryDependenceResults *MemDep) {
64  if (!isa<PHINode>(BB->begin())) return;
65
66  while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
67    if (PN->getIncomingValue(0) != PN)
68      PN->replaceAllUsesWith(PN->getIncomingValue(0));
69    else
70      PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
71
72    if (MemDep)
73      MemDep->removeInstruction(PN);  // Memdep updates AA itself.
74
75    PN->eraseFromParent();
76  }
77}
78
79bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
80  // Recursively deleting a PHI may cause multiple PHIs to be deleted
81  // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
82  SmallVector<WeakVH, 8> PHIs;
83  for (BasicBlock::iterator I = BB->begin();
84       PHINode *PN = dyn_cast<PHINode>(I); ++I)
85    PHIs.push_back(PN);
86
87  bool Changed = false;
88  for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
89    if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
90      Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
91
92  return Changed;
93}
94
95bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
96                                     LoopInfo *LI,
97                                     MemoryDependenceResults *MemDep) {
98  // Don't merge away blocks who have their address taken.
99  if (BB->hasAddressTaken()) return false;
100
101  // Can't merge if there are multiple predecessors, or no predecessors.
102  BasicBlock *PredBB = BB->getUniquePredecessor();
103  if (!PredBB) return false;
104
105  // Don't break self-loops.
106  if (PredBB == BB) return false;
107  // Don't break unwinding instructions.
108  if (PredBB->getTerminator()->isExceptional())
109    return false;
110
111  succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
112  BasicBlock *OnlySucc = BB;
113  for (; SI != SE; ++SI)
114    if (*SI != OnlySucc) {
115      OnlySucc = nullptr;     // There are multiple distinct successors!
116      break;
117    }
118
119  // Can't merge if there are multiple successors.
120  if (!OnlySucc) return false;
121
122  // Can't merge if there is PHI loop.
123  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
124    if (PHINode *PN = dyn_cast<PHINode>(BI)) {
125      for (Value *IncValue : PN->incoming_values())
126        if (IncValue == PN)
127          return false;
128    } else
129      break;
130  }
131
132  // Begin by getting rid of unneeded PHIs.
133  if (isa<PHINode>(BB->front()))
134    FoldSingleEntryPHINodes(BB, MemDep);
135
136  // Delete the unconditional branch from the predecessor...
137  PredBB->getInstList().pop_back();
138
139  // Make all PHI nodes that referred to BB now refer to Pred as their
140  // source...
141  BB->replaceAllUsesWith(PredBB);
142
143  // Move all definitions in the successor to the predecessor...
144  PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
145
146  // Inherit predecessors name if it exists.
147  if (!PredBB->hasName())
148    PredBB->takeName(BB);
149
150  // Finally, erase the old block and update dominator info.
151  if (DT)
152    if (DomTreeNode *DTN = DT->getNode(BB)) {
153      DomTreeNode *PredDTN = DT->getNode(PredBB);
154      SmallVector<DomTreeNode *, 8> Children(DTN->begin(), DTN->end());
155      for (DomTreeNode *DI : Children)
156        DT->changeImmediateDominator(DI, PredDTN);
157
158      DT->eraseNode(BB);
159    }
160
161  if (LI)
162    LI->removeBlock(BB);
163
164  if (MemDep)
165    MemDep->invalidateCachedPredecessors();
166
167  BB->eraseFromParent();
168  return true;
169}
170
171void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
172                                BasicBlock::iterator &BI, Value *V) {
173  Instruction &I = *BI;
174  // Replaces all of the uses of the instruction with uses of the value
175  I.replaceAllUsesWith(V);
176
177  // Make sure to propagate a name if there is one already.
178  if (I.hasName() && !V->hasName())
179    V->takeName(&I);
180
181  // Delete the unnecessary instruction now...
182  BI = BIL.erase(BI);
183}
184
185void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
186                               BasicBlock::iterator &BI, Instruction *I) {
187  assert(I->getParent() == nullptr &&
188         "ReplaceInstWithInst: Instruction already inserted into basic block!");
189
190  // Copy debug location to newly added instruction, if it wasn't already set
191  // by the caller.
192  if (!I->getDebugLoc())
193    I->setDebugLoc(BI->getDebugLoc());
194
195  // Insert the new instruction into the basic block...
196  BasicBlock::iterator New = BIL.insert(BI, I);
197
198  // Replace all uses of the old instruction, and delete it.
199  ReplaceInstWithValue(BIL, BI, I);
200
201  // Move BI back to point to the newly inserted instruction
202  BI = New;
203}
204
205void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
206  BasicBlock::iterator BI(From);
207  ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
208}
209
210BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
211                            LoopInfo *LI) {
212  unsigned SuccNum = GetSuccessorNumber(BB, Succ);
213
214  // If this is a critical edge, let SplitCriticalEdge do it.
215  TerminatorInst *LatchTerm = BB->getTerminator();
216  if (SplitCriticalEdge(LatchTerm, SuccNum, CriticalEdgeSplittingOptions(DT, LI)
217                                                .setPreserveLCSSA()))
218    return LatchTerm->getSuccessor(SuccNum);
219
220  // If the edge isn't critical, then BB has a single successor or Succ has a
221  // single pred.  Split the block.
222  if (BasicBlock *SP = Succ->getSinglePredecessor()) {
223    // If the successor only has a single pred, split the top of the successor
224    // block.
225    assert(SP == BB && "CFG broken");
226    SP = nullptr;
227    return SplitBlock(Succ, &Succ->front(), DT, LI);
228  }
229
230  // Otherwise, if BB has a single successor, split it at the bottom of the
231  // block.
232  assert(BB->getTerminator()->getNumSuccessors() == 1 &&
233         "Should have a single succ!");
234  return SplitBlock(BB, BB->getTerminator(), DT, LI);
235}
236
237unsigned
238llvm::SplitAllCriticalEdges(Function &F,
239                            const CriticalEdgeSplittingOptions &Options) {
240  unsigned NumBroken = 0;
241  for (BasicBlock &BB : F) {
242    TerminatorInst *TI = BB.getTerminator();
243    if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
244      for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
245        if (SplitCriticalEdge(TI, i, Options))
246          ++NumBroken;
247  }
248  return NumBroken;
249}
250
251BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
252                             DominatorTree *DT, LoopInfo *LI) {
253  BasicBlock::iterator SplitIt = SplitPt->getIterator();
254  while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
255    ++SplitIt;
256  BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
257
258  // The new block lives in whichever loop the old one did. This preserves
259  // LCSSA as well, because we force the split point to be after any PHI nodes.
260  if (LI)
261    if (Loop *L = LI->getLoopFor(Old))
262      L->addBasicBlockToLoop(New, *LI);
263
264  if (DT)
265    // Old dominates New. New node dominates all other nodes dominated by Old.
266    if (DomTreeNode *OldNode = DT->getNode(Old)) {
267      std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
268
269      DomTreeNode *NewNode = DT->addNewBlock(New, Old);
270      for (DomTreeNode *I : Children)
271        DT->changeImmediateDominator(I, NewNode);
272    }
273
274  return New;
275}
276
277/// Update DominatorTree, LoopInfo, and LCCSA analysis information.
278static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
279                                      ArrayRef<BasicBlock *> Preds,
280                                      DominatorTree *DT, LoopInfo *LI,
281                                      bool PreserveLCSSA, bool &HasLoopExit) {
282  // Update dominator tree if available.
283  if (DT)
284    DT->splitBlock(NewBB);
285
286  // The rest of the logic is only relevant for updating the loop structures.
287  if (!LI)
288    return;
289
290  Loop *L = LI->getLoopFor(OldBB);
291
292  // If we need to preserve loop analyses, collect some information about how
293  // this split will affect loops.
294  bool IsLoopEntry = !!L;
295  bool SplitMakesNewLoopHeader = false;
296  for (BasicBlock *Pred : Preds) {
297    // If we need to preserve LCSSA, determine if any of the preds is a loop
298    // exit.
299    if (PreserveLCSSA)
300      if (Loop *PL = LI->getLoopFor(Pred))
301        if (!PL->contains(OldBB))
302          HasLoopExit = true;
303
304    // If we need to preserve LoopInfo, note whether any of the preds crosses
305    // an interesting loop boundary.
306    if (!L)
307      continue;
308    if (L->contains(Pred))
309      IsLoopEntry = false;
310    else
311      SplitMakesNewLoopHeader = true;
312  }
313
314  // Unless we have a loop for OldBB, nothing else to do here.
315  if (!L)
316    return;
317
318  if (IsLoopEntry) {
319    // Add the new block to the nearest enclosing loop (and not an adjacent
320    // loop). To find this, examine each of the predecessors and determine which
321    // loops enclose them, and select the most-nested loop which contains the
322    // loop containing the block being split.
323    Loop *InnermostPredLoop = nullptr;
324    for (BasicBlock *Pred : Preds) {
325      if (Loop *PredLoop = LI->getLoopFor(Pred)) {
326        // Seek a loop which actually contains the block being split (to avoid
327        // adjacent loops).
328        while (PredLoop && !PredLoop->contains(OldBB))
329          PredLoop = PredLoop->getParentLoop();
330
331        // Select the most-nested of these loops which contains the block.
332        if (PredLoop && PredLoop->contains(OldBB) &&
333            (!InnermostPredLoop ||
334             InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
335          InnermostPredLoop = PredLoop;
336      }
337    }
338
339    if (InnermostPredLoop)
340      InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
341  } else {
342    L->addBasicBlockToLoop(NewBB, *LI);
343    if (SplitMakesNewLoopHeader)
344      L->moveToHeader(NewBB);
345  }
346}
347
348/// Update the PHI nodes in OrigBB to include the values coming from NewBB.
349/// This also updates AliasAnalysis, if available.
350static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
351                           ArrayRef<BasicBlock *> Preds, BranchInst *BI,
352                           bool HasLoopExit) {
353  // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
354  SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
355  for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
356    PHINode *PN = cast<PHINode>(I++);
357
358    // Check to see if all of the values coming in are the same.  If so, we
359    // don't need to create a new PHI node, unless it's needed for LCSSA.
360    Value *InVal = nullptr;
361    if (!HasLoopExit) {
362      InVal = PN->getIncomingValueForBlock(Preds[0]);
363      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
364        if (!PredSet.count(PN->getIncomingBlock(i)))
365          continue;
366        if (!InVal)
367          InVal = PN->getIncomingValue(i);
368        else if (InVal != PN->getIncomingValue(i)) {
369          InVal = nullptr;
370          break;
371        }
372      }
373    }
374
375    if (InVal) {
376      // If all incoming values for the new PHI would be the same, just don't
377      // make a new PHI.  Instead, just remove the incoming values from the old
378      // PHI.
379
380      // NOTE! This loop walks backwards for a reason! First off, this minimizes
381      // the cost of removal if we end up removing a large number of values, and
382      // second off, this ensures that the indices for the incoming values
383      // aren't invalidated when we remove one.
384      for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
385        if (PredSet.count(PN->getIncomingBlock(i)))
386          PN->removeIncomingValue(i, false);
387
388      // Add an incoming value to the PHI node in the loop for the preheader
389      // edge.
390      PN->addIncoming(InVal, NewBB);
391      continue;
392    }
393
394    // If the values coming into the block are not the same, we need a new
395    // PHI.
396    // Create the new PHI node, insert it into NewBB at the end of the block
397    PHINode *NewPHI =
398        PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
399
400    // NOTE! This loop walks backwards for a reason! First off, this minimizes
401    // the cost of removal if we end up removing a large number of values, and
402    // second off, this ensures that the indices for the incoming values aren't
403    // invalidated when we remove one.
404    for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
405      BasicBlock *IncomingBB = PN->getIncomingBlock(i);
406      if (PredSet.count(IncomingBB)) {
407        Value *V = PN->removeIncomingValue(i, false);
408        NewPHI->addIncoming(V, IncomingBB);
409      }
410    }
411
412    PN->addIncoming(NewPHI, NewBB);
413  }
414}
415
416BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
417                                         ArrayRef<BasicBlock *> Preds,
418                                         const char *Suffix, DominatorTree *DT,
419                                         LoopInfo *LI, bool PreserveLCSSA) {
420  // Do not attempt to split that which cannot be split.
421  if (!BB->canSplitPredecessors())
422    return nullptr;
423
424  // For the landingpads we need to act a bit differently.
425  // Delegate this work to the SplitLandingPadPredecessors.
426  if (BB->isLandingPad()) {
427    SmallVector<BasicBlock*, 2> NewBBs;
428    std::string NewName = std::string(Suffix) + ".split-lp";
429
430    SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs, DT,
431                                LI, PreserveLCSSA);
432    return NewBBs[0];
433  }
434
435  // Create new basic block, insert right before the original block.
436  BasicBlock *NewBB = BasicBlock::Create(
437      BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
438
439  // The new block unconditionally branches to the old block.
440  BranchInst *BI = BranchInst::Create(BB, NewBB);
441  BI->setDebugLoc(BB->getFirstNonPHI()->getDebugLoc());
442
443  // Move the edges from Preds to point to NewBB instead of BB.
444  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
445    // This is slightly more strict than necessary; the minimum requirement
446    // is that there be no more than one indirectbr branching to BB. And
447    // all BlockAddress uses would need to be updated.
448    assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
449           "Cannot split an edge from an IndirectBrInst");
450    Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
451  }
452
453  // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
454  // node becomes an incoming value for BB's phi node.  However, if the Preds
455  // list is empty, we need to insert dummy entries into the PHI nodes in BB to
456  // account for the newly created predecessor.
457  if (Preds.size() == 0) {
458    // Insert dummy values as the incoming value.
459    for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
460      cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
461    return NewBB;
462  }
463
464  // Update DominatorTree, LoopInfo, and LCCSA analysis information.
465  bool HasLoopExit = false;
466  UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, PreserveLCSSA,
467                            HasLoopExit);
468
469  // Update the PHI nodes in BB with the values coming from NewBB.
470  UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
471  return NewBB;
472}
473
474void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
475                                       ArrayRef<BasicBlock *> Preds,
476                                       const char *Suffix1, const char *Suffix2,
477                                       SmallVectorImpl<BasicBlock *> &NewBBs,
478                                       DominatorTree *DT, LoopInfo *LI,
479                                       bool PreserveLCSSA) {
480  assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
481
482  // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
483  // it right before the original block.
484  BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
485                                          OrigBB->getName() + Suffix1,
486                                          OrigBB->getParent(), OrigBB);
487  NewBBs.push_back(NewBB1);
488
489  // The new block unconditionally branches to the old block.
490  BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
491  BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
492
493  // Move the edges from Preds to point to NewBB1 instead of OrigBB.
494  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
495    // This is slightly more strict than necessary; the minimum requirement
496    // is that there be no more than one indirectbr branching to BB. And
497    // all BlockAddress uses would need to be updated.
498    assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
499           "Cannot split an edge from an IndirectBrInst");
500    Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
501  }
502
503  bool HasLoopExit = false;
504  UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, PreserveLCSSA,
505                            HasLoopExit);
506
507  // Update the PHI nodes in OrigBB with the values coming from NewBB1.
508  UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, HasLoopExit);
509
510  // Move the remaining edges from OrigBB to point to NewBB2.
511  SmallVector<BasicBlock*, 8> NewBB2Preds;
512  for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
513       i != e; ) {
514    BasicBlock *Pred = *i++;
515    if (Pred == NewBB1) continue;
516    assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
517           "Cannot split an edge from an IndirectBrInst");
518    NewBB2Preds.push_back(Pred);
519    e = pred_end(OrigBB);
520  }
521
522  BasicBlock *NewBB2 = nullptr;
523  if (!NewBB2Preds.empty()) {
524    // Create another basic block for the rest of OrigBB's predecessors.
525    NewBB2 = BasicBlock::Create(OrigBB->getContext(),
526                                OrigBB->getName() + Suffix2,
527                                OrigBB->getParent(), OrigBB);
528    NewBBs.push_back(NewBB2);
529
530    // The new block unconditionally branches to the old block.
531    BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
532    BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
533
534    // Move the remaining edges from OrigBB to point to NewBB2.
535    for (BasicBlock *NewBB2Pred : NewBB2Preds)
536      NewBB2Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
537
538    // Update DominatorTree, LoopInfo, and LCCSA analysis information.
539    HasLoopExit = false;
540    UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI,
541                              PreserveLCSSA, HasLoopExit);
542
543    // Update the PHI nodes in OrigBB with the values coming from NewBB2.
544    UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, HasLoopExit);
545  }
546
547  LandingPadInst *LPad = OrigBB->getLandingPadInst();
548  Instruction *Clone1 = LPad->clone();
549  Clone1->setName(Twine("lpad") + Suffix1);
550  NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
551
552  if (NewBB2) {
553    Instruction *Clone2 = LPad->clone();
554    Clone2->setName(Twine("lpad") + Suffix2);
555    NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
556
557    // Create a PHI node for the two cloned landingpad instructions only
558    // if the original landingpad instruction has some uses.
559    if (!LPad->use_empty()) {
560      assert(!LPad->getType()->isTokenTy() &&
561             "Split cannot be applied if LPad is token type. Otherwise an "
562             "invalid PHINode of token type would be created.");
563      PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
564      PN->addIncoming(Clone1, NewBB1);
565      PN->addIncoming(Clone2, NewBB2);
566      LPad->replaceAllUsesWith(PN);
567    }
568    LPad->eraseFromParent();
569  } else {
570    // There is no second clone. Just replace the landing pad with the first
571    // clone.
572    LPad->replaceAllUsesWith(Clone1);
573    LPad->eraseFromParent();
574  }
575}
576
577ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
578                                             BasicBlock *Pred) {
579  Instruction *UncondBranch = Pred->getTerminator();
580  // Clone the return and add it to the end of the predecessor.
581  Instruction *NewRet = RI->clone();
582  Pred->getInstList().push_back(NewRet);
583
584  // If the return instruction returns a value, and if the value was a
585  // PHI node in "BB", propagate the right value into the return.
586  for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
587       i != e; ++i) {
588    Value *V = *i;
589    Instruction *NewBC = nullptr;
590    if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
591      // Return value might be bitcasted. Clone and insert it before the
592      // return instruction.
593      V = BCI->getOperand(0);
594      NewBC = BCI->clone();
595      Pred->getInstList().insert(NewRet->getIterator(), NewBC);
596      *i = NewBC;
597    }
598    if (PHINode *PN = dyn_cast<PHINode>(V)) {
599      if (PN->getParent() == BB) {
600        if (NewBC)
601          NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
602        else
603          *i = PN->getIncomingValueForBlock(Pred);
604      }
605    }
606  }
607
608  // Update any PHI nodes in the returning block to realize that we no
609  // longer branch to them.
610  BB->removePredecessor(Pred);
611  UncondBranch->eraseFromParent();
612  return cast<ReturnInst>(NewRet);
613}
614
615TerminatorInst *
616llvm::SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
617                                bool Unreachable, MDNode *BranchWeights,
618                                DominatorTree *DT, LoopInfo *LI) {
619  BasicBlock *Head = SplitBefore->getParent();
620  BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
621  TerminatorInst *HeadOldTerm = Head->getTerminator();
622  LLVMContext &C = Head->getContext();
623  BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
624  TerminatorInst *CheckTerm;
625  if (Unreachable)
626    CheckTerm = new UnreachableInst(C, ThenBlock);
627  else
628    CheckTerm = BranchInst::Create(Tail, ThenBlock);
629  CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
630  BranchInst *HeadNewTerm =
631    BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
632  HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
633  ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
634
635  if (DT) {
636    if (DomTreeNode *OldNode = DT->getNode(Head)) {
637      std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
638
639      DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
640      for (DomTreeNode *Child : Children)
641        DT->changeImmediateDominator(Child, NewNode);
642
643      // Head dominates ThenBlock.
644      DT->addNewBlock(ThenBlock, Head);
645    }
646  }
647
648  if (LI) {
649    Loop *L = LI->getLoopFor(Head);
650    L->addBasicBlockToLoop(ThenBlock, *LI);
651    L->addBasicBlockToLoop(Tail, *LI);
652  }
653
654  return CheckTerm;
655}
656
657void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
658                                         TerminatorInst **ThenTerm,
659                                         TerminatorInst **ElseTerm,
660                                         MDNode *BranchWeights) {
661  BasicBlock *Head = SplitBefore->getParent();
662  BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
663  TerminatorInst *HeadOldTerm = Head->getTerminator();
664  LLVMContext &C = Head->getContext();
665  BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
666  BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
667  *ThenTerm = BranchInst::Create(Tail, ThenBlock);
668  (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
669  *ElseTerm = BranchInst::Create(Tail, ElseBlock);
670  (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
671  BranchInst *HeadNewTerm =
672    BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
673  HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
674  ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
675}
676
677
678Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
679                             BasicBlock *&IfFalse) {
680  PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
681  BasicBlock *Pred1 = nullptr;
682  BasicBlock *Pred2 = nullptr;
683
684  if (SomePHI) {
685    if (SomePHI->getNumIncomingValues() != 2)
686      return nullptr;
687    Pred1 = SomePHI->getIncomingBlock(0);
688    Pred2 = SomePHI->getIncomingBlock(1);
689  } else {
690    pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
691    if (PI == PE) // No predecessor
692      return nullptr;
693    Pred1 = *PI++;
694    if (PI == PE) // Only one predecessor
695      return nullptr;
696    Pred2 = *PI++;
697    if (PI != PE) // More than two predecessors
698      return nullptr;
699  }
700
701  // We can only handle branches.  Other control flow will be lowered to
702  // branches if possible anyway.
703  BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
704  BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
705  if (!Pred1Br || !Pred2Br)
706    return nullptr;
707
708  // Eliminate code duplication by ensuring that Pred1Br is conditional if
709  // either are.
710  if (Pred2Br->isConditional()) {
711    // If both branches are conditional, we don't have an "if statement".  In
712    // reality, we could transform this case, but since the condition will be
713    // required anyway, we stand no chance of eliminating it, so the xform is
714    // probably not profitable.
715    if (Pred1Br->isConditional())
716      return nullptr;
717
718    std::swap(Pred1, Pred2);
719    std::swap(Pred1Br, Pred2Br);
720  }
721
722  if (Pred1Br->isConditional()) {
723    // The only thing we have to watch out for here is to make sure that Pred2
724    // doesn't have incoming edges from other blocks.  If it does, the condition
725    // doesn't dominate BB.
726    if (!Pred2->getSinglePredecessor())
727      return nullptr;
728
729    // If we found a conditional branch predecessor, make sure that it branches
730    // to BB and Pred2Br.  If it doesn't, this isn't an "if statement".
731    if (Pred1Br->getSuccessor(0) == BB &&
732        Pred1Br->getSuccessor(1) == Pred2) {
733      IfTrue = Pred1;
734      IfFalse = Pred2;
735    } else if (Pred1Br->getSuccessor(0) == Pred2 &&
736               Pred1Br->getSuccessor(1) == BB) {
737      IfTrue = Pred2;
738      IfFalse = Pred1;
739    } else {
740      // We know that one arm of the conditional goes to BB, so the other must
741      // go somewhere unrelated, and this must not be an "if statement".
742      return nullptr;
743    }
744
745    return Pred1Br->getCondition();
746  }
747
748  // Ok, if we got here, both predecessors end with an unconditional branch to
749  // BB.  Don't panic!  If both blocks only have a single (identical)
750  // predecessor, and THAT is a conditional branch, then we're all ok!
751  BasicBlock *CommonPred = Pred1->getSinglePredecessor();
752  if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
753    return nullptr;
754
755  // Otherwise, if this is a conditional branch, then we can use it!
756  BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
757  if (!BI) return nullptr;
758
759  assert(BI->isConditional() && "Two successors but not conditional?");
760  if (BI->getSuccessor(0) == Pred1) {
761    IfTrue = Pred1;
762    IfFalse = Pred2;
763  } else {
764    IfTrue = Pred2;
765    IfFalse = Pred1;
766  }
767  return BI->getCondition();
768}
769