IfConversion.cpp revision 221a4371f95ebdb25ac7d4363accb35c88cb5ea4 
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
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 file implements the machine instruction level if-conversion pass.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "ifcvt"
15#include "llvm/Function.h"
16#include "llvm/CodeGen/Passes.h"
17#include "llvm/CodeGen/MachineModuleInfo.h"
18#include "llvm/CodeGen/MachineFunctionPass.h"
19#include "llvm/Target/TargetInstrInfo.h"
20#include "llvm/Target/TargetLowering.h"
21#include "llvm/Target/TargetMachine.h"
22#include "llvm/Support/CommandLine.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/ADT/DepthFirstIterator.h"
25#include "llvm/ADT/Statistic.h"
26#include "llvm/ADT/STLExtras.h"
27using namespace llvm;
28
29// Hidden options for help debugging.
30static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
31static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
32static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
33static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
34                                   cl::init(false), cl::Hidden);
35static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
36                                    cl::init(false), cl::Hidden);
37static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
38                                     cl::init(false), cl::Hidden);
39static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
40                                      cl::init(false), cl::Hidden);
41static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
42                                      cl::init(false), cl::Hidden);
43static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
44                                       cl::init(false), cl::Hidden);
45static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
46                                    cl::init(false), cl::Hidden);
47
48STATISTIC(NumSimple,       "Number of simple if-conversions performed");
49STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
50STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
51STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
52STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
53STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
54STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
55STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
56STATISTIC(NumDupBBs,       "Number of duplicated blocks");
57
58namespace {
59  class VISIBILITY_HIDDEN IfConverter : public MachineFunctionPass {
60    enum IfcvtKind {
61      ICNotClassfied,  // BB data valid, but not classified.
62      ICSimpleFalse,   // Same as ICSimple, but on the false path.
63      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
64      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
65      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
66      ICTriangleFalse, // Same as ICTriangle, but on the false path.
67      ICTriangle,      // BB is entry of a triangle sub-CFG.
68      ICDiamond        // BB is entry of a diamond sub-CFG.
69    };
70
71    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
72    /// if-conversion feasibility analysis. This includes results from
73    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
74    /// classification, and common tail block of its successors (if it's a
75    /// diamond shape), its size, whether it's predicable, and whether any
76    /// instruction can clobber the 'would-be' predicate.
77    ///
78    /// IsDone          - True if BB is not to be considered for ifcvt.
79    /// IsBeingAnalyzed - True if BB is currently being analyzed.
80    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
81    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
82    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
83    /// HasFallThrough  - True if BB may fallthrough to the following BB.
84    /// IsUnpredicable  - True if BB is known to be unpredicable.
85    /// ClobbersPred    - True if BB could modify predicates (e.g. has
86    ///                   cmp, call, etc.)
87    /// NonPredSize     - Number of non-predicated instructions.
88    /// BB              - Corresponding MachineBasicBlock.
89    /// TrueBB / FalseBB- See AnalyzeBranch().
90    /// BrCond          - Conditions for end of block conditional branches.
91    /// Predicate       - Predicate used in the BB.
92    struct BBInfo {
93      bool IsDone          : 1;
94      bool IsBeingAnalyzed : 1;
95      bool IsAnalyzed      : 1;
96      bool IsEnqueued      : 1;
97      bool IsBrAnalyzable  : 1;
98      bool HasFallThrough  : 1;
99      bool IsUnpredicable  : 1;
100      bool CannotBeCopied  : 1;
101      bool ClobbersPred    : 1;
102      unsigned NonPredSize;
103      MachineBasicBlock *BB;
104      MachineBasicBlock *TrueBB;
105      MachineBasicBlock *FalseBB;
106      std::vector<MachineOperand> BrCond;
107      std::vector<MachineOperand> Predicate;
108      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
109                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
110                 HasFallThrough(false), IsUnpredicable(false),
111                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
112                 BB(0), TrueBB(0), FalseBB(0) {}
113    };
114
115    /// IfcvtToken - Record information about pending if-conversions to attemp:
116    /// BBI             - Corresponding BBInfo.
117    /// Kind            - Type of block. See IfcvtKind.
118    /// NeedSubsumsion  - True if the to be predicated BB has already been
119    ///                   predicated.
120    /// NumDups      - Number of instructions that would be duplicated due
121    ///                   to this if-conversion. (For diamonds, the number of
122    ///                   identical instructions at the beginnings of both
123    ///                   paths).
124    /// NumDups2     - For diamonds, the number of identical instructions
125    ///                   at the ends of both paths.
126    struct IfcvtToken {
127      BBInfo &BBI;
128      IfcvtKind Kind;
129      bool NeedSubsumsion;
130      unsigned NumDups;
131      unsigned NumDups2;
132      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
133        : BBI(b), Kind(k), NeedSubsumsion(s), NumDups(d), NumDups2(d2) {}
134    };
135
136    /// Roots - Basic blocks that do not have successors. These are the starting
137    /// points of Graph traversal.
138    std::vector<MachineBasicBlock*> Roots;
139
140    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
141    /// basic block number.
142    std::vector<BBInfo> BBAnalysis;
143
144    const TargetLowering *TLI;
145    const TargetInstrInfo *TII;
146    bool MadeChange;
147  public:
148    static char ID;
149    IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
150
151    virtual bool runOnMachineFunction(MachineFunction &MF);
152    virtual const char *getPassName() const { return "If Converter"; }
153
154  private:
155    bool ReverseBranchCondition(BBInfo &BBI);
156    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
157    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
158                       bool FalseBranch, unsigned &Dups) const;
159    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
160                      unsigned &Dups1, unsigned &Dups2) const;
161    void ScanInstructions(BBInfo &BBI);
162    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
163                         std::vector<IfcvtToken*> &Tokens);
164    bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
165                             bool isTriangle = false, bool RevBranch = false);
166    bool AnalyzeBlocks(MachineFunction &MF,
167                       std::vector<IfcvtToken*> &Tokens);
168    void InvalidatePreds(MachineBasicBlock *BB);
169    void RemoveExtraEdges(BBInfo &BBI);
170    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
171    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
172    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
173                          unsigned NumDups1, unsigned NumDups2);
174    void PredicateBlock(BBInfo &BBI,
175                        MachineBasicBlock::iterator E,
176                        std::vector<MachineOperand> &Cond);
177    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
178                               std::vector<MachineOperand> &Cond,
179                               bool IgnoreBr = false);
180    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
181
182    bool MeetIfcvtSizeLimit(unsigned Size) const {
183      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
184    }
185
186    // blockAlwaysFallThrough - Block ends without a terminator.
187    bool blockAlwaysFallThrough(BBInfo &BBI) const {
188      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
189    }
190
191    // IfcvtTokenCmp - Used to sort if-conversion candidates.
192    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
193      int Incr1 = (C1->Kind == ICDiamond)
194        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
195      int Incr2 = (C2->Kind == ICDiamond)
196        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
197      if (Incr1 > Incr2)
198        return true;
199      else if (Incr1 == Incr2) {
200        // Favors subsumsion.
201        if (C1->NeedSubsumsion == false && C2->NeedSubsumsion == true)
202          return true;
203        else if (C1->NeedSubsumsion == C2->NeedSubsumsion) {
204          // Favors diamond over triangle, etc.
205          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
206            return true;
207          else if (C1->Kind == C2->Kind)
208            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
209        }
210      }
211      return false;
212    }
213  };
214
215  char IfConverter::ID = 0;
216}
217
218static RegisterPass<IfConverter>
219X("if-converter", "If Converter");
220
221FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
222
223bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
224  TLI = MF.getTarget().getTargetLowering();
225  TII = MF.getTarget().getInstrInfo();
226  if (!TII) return false;
227
228  static int FnNum = -1;
229  DOUT << "\nIfcvt: function (" << ++FnNum <<  ") \'"
230       << MF.getFunction()->getName() << "\'";
231
232  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
233    DOUT << " skipped\n";
234    return false;
235  }
236  DOUT << "\n";
237
238  MF.RenumberBlocks();
239  BBAnalysis.resize(MF.getNumBlockIDs());
240
241  // Look for root nodes, i.e. blocks without successors.
242  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
243    if (I->succ_empty())
244      Roots.push_back(I);
245
246  std::vector<IfcvtToken*> Tokens;
247  MadeChange = false;
248  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
249    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
250  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
251    // Do an intial analysis for each basic block and finding all the potential
252    // candidates to perform if-convesion.
253    bool Change = AnalyzeBlocks(MF, Tokens);
254    while (!Tokens.empty()) {
255      IfcvtToken *Token = Tokens.back();
256      Tokens.pop_back();
257      BBInfo &BBI = Token->BBI;
258      IfcvtKind Kind = Token->Kind;
259
260      // If the block has been evicted out of the queue or it has already been
261      // marked dead (due to it being predicated), then skip it.
262      if (BBI.IsDone)
263        BBI.IsEnqueued = false;
264      if (!BBI.IsEnqueued)
265        continue;
266
267      BBI.IsEnqueued = false;
268
269      bool RetVal = false;
270      switch (Kind) {
271      default: assert(false && "Unexpected!");
272        break;
273      case ICSimple:
274      case ICSimpleFalse: {
275        bool isFalse = Kind == ICSimpleFalse;
276        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
277        DOUT << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
278             << "): BB#" << BBI.BB->getNumber() << " ("
279             << ((Kind == ICSimpleFalse)
280                 ? BBI.FalseBB->getNumber()
281                 : BBI.TrueBB->getNumber()) << ") ";
282        RetVal = IfConvertSimple(BBI, Kind);
283        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
284        if (RetVal) {
285          if (isFalse) NumSimpleFalse++;
286          else         NumSimple++;
287        }
288       break;
289      }
290      case ICTriangle:
291      case ICTriangleRev:
292      case ICTriangleFalse:
293      case ICTriangleFRev: {
294        bool isFalse = Kind == ICTriangleFalse;
295        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
296        if (DisableTriangle && !isFalse && !isRev) break;
297        if (DisableTriangleR && !isFalse && isRev) break;
298        if (DisableTriangleF && isFalse && !isRev) break;
299        if (DisableTriangleFR && isFalse && isRev) break;
300        DOUT << "Ifcvt (Triangle";
301        if (isFalse)
302          DOUT << " false";
303        if (isRev)
304          DOUT << " rev";
305        DOUT << "): BB#" << BBI.BB->getNumber() << " (T:"
306             << BBI.TrueBB->getNumber() << ",F:"
307             << BBI.FalseBB->getNumber() << ") ";
308        RetVal = IfConvertTriangle(BBI, Kind);
309        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
310        if (RetVal) {
311          if (isFalse) {
312            if (isRev) NumTriangleFRev++;
313            else       NumTriangleFalse++;
314          } else {
315            if (isRev) NumTriangleRev++;
316            else       NumTriangle++;
317          }
318        }
319        break;
320      }
321      case ICDiamond: {
322        if (DisableDiamond) break;
323        DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
324             << BBI.TrueBB->getNumber() << ",F:"
325             << BBI.FalseBB->getNumber() << ") ";
326        RetVal = IfConvertDiamond(BBI, Kind, Token->NumDups, Token->NumDups2);
327        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
328        if (RetVal) NumDiamonds++;
329        break;
330      }
331      }
332
333      Change |= RetVal;
334
335      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
336        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
337      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
338        break;
339    }
340
341    if (!Change)
342      break;
343    MadeChange |= Change;
344  }
345
346  // Delete tokens in case of early exit.
347  while (!Tokens.empty()) {
348    IfcvtToken *Token = Tokens.back();
349    Tokens.pop_back();
350    delete Token;
351  }
352
353  Tokens.clear();
354  Roots.clear();
355  BBAnalysis.clear();
356
357  return MadeChange;
358}
359
360/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
361/// its 'true' successor.
362static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
363                                         MachineBasicBlock *TrueBB) {
364  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
365         E = BB->succ_end(); SI != E; ++SI) {
366    MachineBasicBlock *SuccBB = *SI;
367    if (SuccBB != TrueBB)
368      return SuccBB;
369  }
370  return NULL;
371}
372
373/// ReverseBranchCondition - Reverse the condition of the end of the block
374/// branchs. Swap block's 'true' and 'false' successors.
375bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
376  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
377    TII->RemoveBranch(*BBI.BB);
378    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
379    std::swap(BBI.TrueBB, BBI.FalseBB);
380    return true;
381  }
382  return false;
383}
384
385/// getNextBlock - Returns the next block in the function blocks ordering. If
386/// it is the end, returns NULL.
387static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
388  MachineFunction::iterator I = BB;
389  MachineFunction::iterator E = BB->getParent()->end();
390  if (++I == E)
391    return NULL;
392  return I;
393}
394
395/// ValidSimple - Returns true if the 'true' block (along with its
396/// predecessor) forms a valid simple shape for ifcvt. It also returns the
397/// number of instructions that the ifcvt would need to duplicate if performed
398/// in Dups.
399bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
400  Dups = 0;
401  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
402    return false;
403
404  if (TrueBBI.IsBrAnalyzable)
405    return false;
406
407  if (TrueBBI.BB->pred_size() > 1) {
408    if (TrueBBI.CannotBeCopied ||
409        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
410      return false;
411    Dups = TrueBBI.NonPredSize;
412  }
413
414  return true;
415}
416
417/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
418/// with their common predecessor) forms a valid triangle shape for ifcvt.
419/// If 'FalseBranch' is true, it checks if 'true' block's false branch
420/// branches to the false branch rather than the other way around. It also
421/// returns the number of instructions that the ifcvt would need to duplicate
422/// if performed in 'Dups'.
423bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
424                                bool FalseBranch, unsigned &Dups) const {
425  Dups = 0;
426  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
427    return false;
428
429  if (TrueBBI.BB->pred_size() > 1) {
430    if (TrueBBI.CannotBeCopied)
431      return false;
432
433    unsigned Size = TrueBBI.NonPredSize;
434    if (TrueBBI.IsBrAnalyzable) {
435      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
436        // End with an unconditional branch. It will be removed.
437        --Size;
438      else {
439        MachineBasicBlock *FExit = FalseBranch
440          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
441        if (FExit)
442          // Require a conditional branch
443          ++Size;
444      }
445    }
446    if (Size > TLI->getIfCvtDupBlockSizeLimit())
447      return false;
448    Dups = Size;
449  }
450
451  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
452  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
453    MachineFunction::iterator I = TrueBBI.BB;
454    if (++I == TrueBBI.BB->getParent()->end())
455      return false;
456    TExit = I;
457  }
458  return TExit && TExit == FalseBBI.BB;
459}
460
461static
462MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
463                                               const TargetInstrInfo *TII) {
464  MachineBasicBlock::iterator I = BB->end();
465  while (I != BB->begin()) {
466    --I;
467    if (!I->getDesc().isBranch())
468      break;
469  }
470  return I;
471}
472
473/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
474/// with their common predecessor) forms a valid diamond shape for ifcvt.
475bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
476                               unsigned &Dups1, unsigned &Dups2) const {
477  Dups1 = Dups2 = 0;
478  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
479      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
480    return false;
481
482  MachineBasicBlock *TT = TrueBBI.TrueBB;
483  MachineBasicBlock *FT = FalseBBI.TrueBB;
484
485  if (!TT && blockAlwaysFallThrough(TrueBBI))
486    TT = getNextBlock(TrueBBI.BB);
487  if (!FT && blockAlwaysFallThrough(FalseBBI))
488    FT = getNextBlock(FalseBBI.BB);
489  if (TT != FT)
490    return false;
491  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
492    return false;
493  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
494    return false;
495
496  // FIXME: Allow true block to have an early exit?
497  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
498      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
499    return false;
500
501  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
502  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
503  while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) {
504    if (!TI->isIdenticalTo(FI))
505      break;
506    ++Dups1;
507    ++TI;
508    ++FI;
509  }
510
511  TI = firstNonBranchInst(TrueBBI.BB, TII);
512  FI = firstNonBranchInst(FalseBBI.BB, TII);
513  while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) {
514    if (!TI->isIdenticalTo(FI))
515      break;
516    ++Dups2;
517    --TI;
518    --FI;
519  }
520
521  return true;
522}
523
524/// ScanInstructions - Scan all the instructions in the block to determine if
525/// the block is predicable. In most cases, that means all the instructions
526/// in the block are isPredicable(). Also checks if the block contains any
527/// instruction which can clobber a predicate (e.g. condition code register).
528/// If so, the block is not predicable unless it's the last instruction.
529void IfConverter::ScanInstructions(BBInfo &BBI) {
530  if (BBI.IsDone)
531    return;
532
533  bool AlreadyPredicated = BBI.Predicate.size() > 0;
534  // First analyze the end of BB branches.
535  BBI.TrueBB = BBI.FalseBB = NULL;
536  BBI.BrCond.clear();
537  BBI.IsBrAnalyzable =
538    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
539  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
540
541  if (BBI.BrCond.size()) {
542    // No false branch. This BB must end with a conditional branch and a
543    // fallthrough.
544    if (!BBI.FalseBB)
545      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
546    assert(BBI.FalseBB && "Expected to find the fallthrough block!");
547  }
548
549  // Then scan all the instructions.
550  BBI.NonPredSize = 0;
551  BBI.ClobbersPred = false;
552  bool SeenCondBr = false;
553  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
554       I != E; ++I) {
555    const TargetInstrDesc &TID = I->getDesc();
556    if (TID.isNotDuplicable())
557      BBI.CannotBeCopied = true;
558
559    bool isPredicated = TII->isPredicated(I);
560    bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
561
562    if (!isCondBr) {
563      if (!isPredicated)
564        BBI.NonPredSize++;
565      else if (!AlreadyPredicated) {
566        // FIXME: This instruction is already predicated before the
567        // if-conversion pass. It's probably something like a conditional move.
568        // Mark this block unpredicable for now.
569        BBI.IsUnpredicable = true;
570        return;
571      }
572
573    }
574
575    if (BBI.ClobbersPred && !isPredicated) {
576      // Predicate modification instruction should end the block (except for
577      // already predicated instructions and end of block branches).
578      if (isCondBr) {
579        SeenCondBr = true;
580
581        // Conditional branches is not predicable. But it may be eliminated.
582        continue;
583      }
584
585      // Predicate may have been modified, the subsequent (currently)
586      // unpredicated instructions cannot be correctly predicated.
587      BBI.IsUnpredicable = true;
588      return;
589    }
590
591    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
592    // still potentially predicable.
593    std::vector<MachineOperand> PredDefs;
594    if (TII->DefinesPredicate(I, PredDefs))
595      BBI.ClobbersPred = true;
596
597    if (!TID.isPredicable()) {
598      BBI.IsUnpredicable = true;
599      return;
600    }
601  }
602}
603
604/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
605/// predicated by the specified predicate.
606bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
607                                      std::vector<MachineOperand> &Pred,
608                                      bool isTriangle, bool RevBranch) {
609  // If the block is dead or unpredicable, then it cannot be predicated.
610  if (BBI.IsDone || BBI.IsUnpredicable)
611    return false;
612
613  // If it is already predicated, check if its predicate subsumes the new
614  // predicate.
615  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
616    return false;
617
618  if (BBI.BrCond.size()) {
619    if (!isTriangle)
620      return false;
621
622    // Test predicate subsumsion.
623    std::vector<MachineOperand> RevPred(Pred);
624    std::vector<MachineOperand> Cond(BBI.BrCond);
625    if (RevBranch) {
626      if (TII->ReverseBranchCondition(Cond))
627        return false;
628    }
629    if (TII->ReverseBranchCondition(RevPred) ||
630        !TII->SubsumesPredicate(Cond, RevPred))
631      return false;
632  }
633
634  return true;
635}
636
637/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
638/// the specified block. Record its successors and whether it looks like an
639/// if-conversion candidate.
640IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
641                                             std::vector<IfcvtToken*> &Tokens) {
642  BBInfo &BBI = BBAnalysis[BB->getNumber()];
643
644  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
645    return BBI;
646
647  BBI.BB = BB;
648  BBI.IsBeingAnalyzed = true;
649
650  ScanInstructions(BBI);
651
652  // Unanalyable or ends with fallthrough or unconditional branch.
653  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
654    BBI.IsBeingAnalyzed = false;
655    BBI.IsAnalyzed = true;
656    return BBI;
657  }
658
659  // Do not ifcvt if either path is a back edge to the entry block.
660  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
661    BBI.IsBeingAnalyzed = false;
662    BBI.IsAnalyzed = true;
663    return BBI;
664  }
665
666  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
667  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
668
669  if (TrueBBI.IsDone && FalseBBI.IsDone) {
670    BBI.IsBeingAnalyzed = false;
671    BBI.IsAnalyzed = true;
672    return BBI;
673  }
674
675  std::vector<MachineOperand> RevCond(BBI.BrCond);
676  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
677
678  unsigned Dups = 0;
679  unsigned Dups2 = 0;
680  bool TNeedSub = TrueBBI.Predicate.size() > 0;
681  bool FNeedSub = FalseBBI.Predicate.size() > 0;
682  bool Enqueued = false;
683  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
684      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
685      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
686      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
687      FeasibilityAnalysis(FalseBBI, RevCond)) {
688    // Diamond:
689    //   EBB
690    //   / \_
691    //  |   |
692    // TBB FBB
693    //   \ /
694    //  TailBB
695    // Note TailBB can be empty.
696    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
697                                    Dups2));
698    Enqueued = true;
699  }
700
701  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
702      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
703      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
704    // Triangle:
705    //   EBB
706    //   | \_
707    //   |  |
708    //   | TBB
709    //   |  /
710    //   FBB
711    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
712    Enqueued = true;
713  }
714
715  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
716      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
717      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
718    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
719    Enqueued = true;
720  }
721
722  if (ValidSimple(TrueBBI, Dups) &&
723      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
724      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
725    // Simple (split, no rejoin):
726    //   EBB
727    //   | \_
728    //   |  |
729    //   | TBB---> exit
730    //   |
731    //   FBB
732    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
733    Enqueued = true;
734  }
735
736  if (CanRevCond) {
737    // Try the other path...
738    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
739        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
740        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
741      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
742      Enqueued = true;
743    }
744
745    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
746        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
747        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
748      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
749      Enqueued = true;
750    }
751
752    if (ValidSimple(FalseBBI, Dups) &&
753        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
754        FeasibilityAnalysis(FalseBBI, RevCond)) {
755      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
756      Enqueued = true;
757    }
758  }
759
760  BBI.IsEnqueued = Enqueued;
761  BBI.IsBeingAnalyzed = false;
762  BBI.IsAnalyzed = true;
763  return BBI;
764}
765
766/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
767/// candidates. It returns true if any CFG restructuring is done to expose more
768/// if-conversion opportunities.
769bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
770                                std::vector<IfcvtToken*> &Tokens) {
771  bool Change = false;
772  std::set<MachineBasicBlock*> Visited;
773  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
774    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
775           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
776      MachineBasicBlock *BB = *I;
777      AnalyzeBlock(BB, Tokens);
778    }
779  }
780
781  // Sort to favor more complex ifcvt scheme.
782  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
783
784  return Change;
785}
786
787/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
788/// that all the intervening blocks are empty (given BB can fall through to its
789/// next block).
790static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
791  MachineFunction::iterator I = BB;
792  MachineFunction::iterator TI = ToBB;
793  MachineFunction::iterator E = BB->getParent()->end();
794  while (++I != TI)
795    if (I == E || !I->empty())
796      return false;
797  return true;
798}
799
800/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
801/// to determine if it can be if-converted. If predecessor is already enqueued,
802/// dequeue it!
803void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
804  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
805         E = BB->pred_end(); PI != E; ++PI) {
806    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
807    if (PBBI.IsDone || PBBI.BB == BB)
808      continue;
809    PBBI.IsAnalyzed = false;
810    PBBI.IsEnqueued = false;
811  }
812}
813
814/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
815///
816static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
817                               const TargetInstrInfo *TII) {
818  std::vector<MachineOperand> NoCond;
819  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
820}
821
822/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
823/// successors.
824void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
825  MachineBasicBlock *TBB = NULL, *FBB = NULL;
826  std::vector<MachineOperand> Cond;
827  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
828    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
829}
830
831/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
832///
833bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
834  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
835  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
836  BBInfo *CvtBBI = &TrueBBI;
837  BBInfo *NextBBI = &FalseBBI;
838
839  std::vector<MachineOperand> Cond(BBI.BrCond);
840  if (Kind == ICSimpleFalse)
841    std::swap(CvtBBI, NextBBI);
842
843  if (CvtBBI->IsDone ||
844      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
845    // Something has changed. It's no longer safe to predicate this block.
846    BBI.IsAnalyzed = false;
847    CvtBBI->IsAnalyzed = false;
848    return false;
849  }
850
851  if (Kind == ICSimpleFalse)
852    TII->ReverseBranchCondition(Cond);
853
854  if (CvtBBI->BB->pred_size() > 1) {
855    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
856    // Copy instructions in the true block, predicate them add them to
857    // the entry block.
858    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
859  } else {
860    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
861
862    // Merge converted block into entry block.
863    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
864    MergeBlocks(BBI, *CvtBBI);
865  }
866
867  bool IterIfcvt = true;
868  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
869    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
870    BBI.HasFallThrough = false;
871    // Now ifcvt'd block will look like this:
872    // BB:
873    // ...
874    // t, f = cmp
875    // if t op
876    // b BBf
877    //
878    // We cannot further ifcvt this block because the unconditional branch
879    // will have to be predicated on the new condition, that will not be
880    // available if cmp executes.
881    IterIfcvt = false;
882  }
883
884  RemoveExtraEdges(BBI);
885
886  // Update block info. BB can be iteratively if-converted.
887  if (!IterIfcvt)
888    BBI.IsDone = true;
889  InvalidatePreds(BBI.BB);
890  CvtBBI->IsDone = true;
891
892  // FIXME: Must maintain LiveIns.
893  return true;
894}
895
896/// IfConvertTriangle - If convert a triangle sub-CFG.
897///
898bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
899  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
900  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
901  BBInfo *CvtBBI = &TrueBBI;
902  BBInfo *NextBBI = &FalseBBI;
903
904  std::vector<MachineOperand> Cond(BBI.BrCond);
905  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
906    std::swap(CvtBBI, NextBBI);
907
908  if (CvtBBI->IsDone ||
909      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
910    // Something has changed. It's no longer safe to predicate this block.
911    BBI.IsAnalyzed = false;
912    CvtBBI->IsAnalyzed = false;
913    return false;
914  }
915
916  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
917    TII->ReverseBranchCondition(Cond);
918
919  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
920    ReverseBranchCondition(*CvtBBI);
921    // BB has been changed, modify its predecessors (except for this
922    // one) so they don't get ifcvt'ed based on bad intel.
923    for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
924           E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
925      MachineBasicBlock *PBB = *PI;
926      if (PBB == BBI.BB)
927        continue;
928      BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
929      if (PBBI.IsEnqueued) {
930        PBBI.IsAnalyzed = false;
931        PBBI.IsEnqueued = false;
932      }
933    }
934  }
935
936  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
937  bool DupBB = CvtBBI->BB->pred_size() > 1;
938  if (DupBB) {
939    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
940    // Copy instructions in the true block, predicate them add them to
941    // the entry block.
942    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
943  } else {
944    // Predicate the 'true' block after removing its branch.
945    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
946    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
947  }
948
949  if (!DupBB) {
950    // Now merge the entry of the triangle with the true block.
951    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
952    MergeBlocks(BBI, *CvtBBI);
953  }
954
955  // If 'true' block has a 'false' successor, add an exit branch to it.
956  if (HasEarlyExit) {
957    std::vector<MachineOperand> RevCond(CvtBBI->BrCond);
958    if (TII->ReverseBranchCondition(RevCond))
959      assert(false && "Unable to reverse branch condition!");
960    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
961    BBI.BB->addSuccessor(CvtBBI->FalseBB);
962  }
963
964  // Merge in the 'false' block if the 'false' block has no other
965  // predecessors. Otherwise, add a unconditional branch from to 'false'.
966  bool FalseBBDead = false;
967  bool IterIfcvt = true;
968  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
969  if (!isFallThrough) {
970    // Only merge them if the true block does not fallthrough to the false
971    // block. By not merging them, we make it possible to iteratively
972    // ifcvt the blocks.
973    if (!HasEarlyExit &&
974        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
975      MergeBlocks(BBI, *NextBBI);
976      FalseBBDead = true;
977    } else {
978      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
979      BBI.HasFallThrough = false;
980    }
981    // Mixed predicated and unpredicated code. This cannot be iteratively
982    // predicated.
983    IterIfcvt = false;
984  }
985
986  RemoveExtraEdges(BBI);
987
988  // Update block info. BB can be iteratively if-converted.
989  if (!IterIfcvt)
990    BBI.IsDone = true;
991  InvalidatePreds(BBI.BB);
992  CvtBBI->IsDone = true;
993  if (FalseBBDead)
994    NextBBI->IsDone = true;
995
996  // FIXME: Must maintain LiveIns.
997  return true;
998}
999
1000/// IfConvertDiamond - If convert a diamond sub-CFG.
1001///
1002bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1003                                   unsigned NumDups1, unsigned NumDups2) {
1004  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1005  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1006  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1007  // True block must fall through or ended with unanalyzable terminator.
1008  if (!TailBB) {
1009    if (blockAlwaysFallThrough(TrueBBI))
1010      TailBB = FalseBBI.TrueBB;
1011    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1012  }
1013
1014  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1015      TrueBBI.BB->pred_size() > 1 ||
1016      FalseBBI.BB->pred_size() > 1) {
1017    // Something has changed. It's no longer safe to predicate these blocks.
1018    BBI.IsAnalyzed = false;
1019    TrueBBI.IsAnalyzed = false;
1020    FalseBBI.IsAnalyzed = false;
1021    return false;
1022  }
1023
1024  // Merge the 'true' and 'false' blocks by copying the instructions
1025  // from the 'false' block to the 'true' block. That is, unless the true
1026  // block would clobber the predicate, in that case, do the opposite.
1027  BBInfo *BBI1 = &TrueBBI;
1028  BBInfo *BBI2 = &FalseBBI;
1029  std::vector<MachineOperand> RevCond(BBI.BrCond);
1030  TII->ReverseBranchCondition(RevCond);
1031  std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
1032  std::vector<MachineOperand> *Cond2 = &RevCond;
1033
1034  // Figure out the more profitable ordering.
1035  bool DoSwap = false;
1036  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1037    DoSwap = true;
1038  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1039    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1040      DoSwap = true;
1041  }
1042  if (DoSwap) {
1043    std::swap(BBI1, BBI2);
1044    std::swap(Cond1, Cond2);
1045  }
1046
1047  // Remove the conditional branch from entry to the blocks.
1048  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1049
1050  // Remove the duplicated instructions at the beginnings of both paths.
1051  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1052  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1053  BBI1->NonPredSize -= NumDups1;
1054  BBI2->NonPredSize -= NumDups1;
1055  while (NumDups1 != 0) {
1056    ++DI1;
1057    ++DI2;
1058    --NumDups1;
1059  }
1060  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1061  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1062
1063  // Predicate the 'true' block after removing its branch.
1064  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1065  DI1 = BBI1->BB->end();
1066  for (unsigned i = 0; i != NumDups2; ++i)
1067    --DI1;
1068  BBI1->BB->erase(DI1, BBI1->BB->end());
1069  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1070
1071  // Predicate the 'false' block.
1072  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1073  DI2 = BBI2->BB->end();
1074  while (NumDups2 != 0) {
1075    --DI2;
1076    --NumDups2;
1077  }
1078  PredicateBlock(*BBI2, DI2, *Cond2);
1079
1080  // Merge the true block into the entry of the diamond.
1081  MergeBlocks(BBI, *BBI1);
1082  MergeBlocks(BBI, *BBI2);
1083
1084  // If the if-converted block fallthrough or unconditionally branch into the
1085  // tail block, and the tail block does not have other predecessors, then
1086  // fold the tail block in as well. Otherwise, unless it falls through to the
1087  // tail, add a unconditional branch to it.
1088  if (TailBB) {
1089    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1090    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1091      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1092      MergeBlocks(BBI, TailBBI);
1093      TailBBI.IsDone = true;
1094    } else {
1095      InsertUncondBranch(BBI.BB, TailBB, TII);
1096      BBI.HasFallThrough = false;
1097    }
1098  }
1099
1100  RemoveExtraEdges(BBI);
1101
1102  // Update block info.
1103  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1104  InvalidatePreds(BBI.BB);
1105
1106  // FIXME: Must maintain LiveIns.
1107  return true;
1108}
1109
1110/// PredicateBlock - Predicate instructions from the start of the block to the
1111/// specified end with the specified condition.
1112void IfConverter::PredicateBlock(BBInfo &BBI,
1113                                 MachineBasicBlock::iterator E,
1114                                 std::vector<MachineOperand> &Cond) {
1115  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1116    if (TII->isPredicated(I))
1117      continue;
1118    if (!TII->PredicateInstruction(I, Cond)) {
1119      cerr << "Unable to predicate " << *I << "!\n";
1120      abort();
1121    }
1122  }
1123
1124  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1125
1126  BBI.IsAnalyzed = false;
1127  BBI.NonPredSize = 0;
1128
1129  NumIfConvBBs++;
1130}
1131
1132/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1133/// the destination block. Skip end of block branches if IgnoreBr is true.
1134void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1135                                        std::vector<MachineOperand> &Cond,
1136                                        bool IgnoreBr) {
1137  MachineFunction &MF = *ToBBI.BB->getParent();
1138
1139  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1140         E = FromBBI.BB->end(); I != E; ++I) {
1141    const TargetInstrDesc &TID = I->getDesc();
1142    bool isPredicated = TII->isPredicated(I);
1143    // Do not copy the end of the block branches.
1144    if (IgnoreBr && !isPredicated && TID.isBranch())
1145      break;
1146
1147    MachineInstr *MI = MF.CloneMachineInstr(I);
1148    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1149    ToBBI.NonPredSize++;
1150
1151    if (!isPredicated)
1152      if (!TII->PredicateInstruction(MI, Cond)) {
1153        cerr << "Unable to predicate " << *MI << "!\n";
1154        abort();
1155      }
1156  }
1157
1158  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1159                                         FromBBI.BB->succ_end());
1160  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1161  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1162
1163  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1164    MachineBasicBlock *Succ = Succs[i];
1165    // Fallthrough edge can't be transferred.
1166    if (Succ == FallThrough)
1167      continue;
1168    if (!ToBBI.BB->isSuccessor(Succ))
1169      ToBBI.BB->addSuccessor(Succ);
1170  }
1171
1172  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1173            std::back_inserter(ToBBI.Predicate));
1174  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1175
1176  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1177  ToBBI.IsAnalyzed = false;
1178
1179  NumDupBBs++;
1180}
1181
1182/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1183///
1184void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1185  ToBBI.BB->splice(ToBBI.BB->end(),
1186                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1187
1188  // Redirect all branches to FromBB to ToBB.
1189  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1190                                         FromBBI.BB->pred_end());
1191  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1192    MachineBasicBlock *Pred = Preds[i];
1193    if (Pred == ToBBI.BB)
1194      continue;
1195    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1196  }
1197
1198  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1199                                         FromBBI.BB->succ_end());
1200  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1201  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1202
1203  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1204    MachineBasicBlock *Succ = Succs[i];
1205    // Fallthrough edge can't be transferred.
1206    if (Succ == FallThrough)
1207      continue;
1208    FromBBI.BB->removeSuccessor(Succ);
1209    if (!ToBBI.BB->isSuccessor(Succ))
1210      ToBBI.BB->addSuccessor(Succ);
1211  }
1212
1213  // Now FromBBI always fall through to the next block!
1214  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1215    FromBBI.BB->addSuccessor(NBB);
1216
1217  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1218            std::back_inserter(ToBBI.Predicate));
1219  FromBBI.Predicate.clear();
1220
1221  ToBBI.NonPredSize += FromBBI.NonPredSize;
1222  FromBBI.NonPredSize = 0;
1223
1224  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1225  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1226  ToBBI.IsAnalyzed = false;
1227  FromBBI.IsAnalyzed = false;
1228}
1229