IfConversion.cpp revision 5f70218c7534d7214cc23b7151ab25771bd3151b 
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the Evan Cheng and is distributed under
6// the University of Illinois Open Source 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/Debug.h"
23#include "llvm/ADT/DepthFirstIterator.h"
24#include "llvm/ADT/Statistic.h"
25using namespace llvm;
26
27STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
28
29namespace {
30  class IfConverter : public MachineFunctionPass {
31    enum BBICKind {
32      ICNotAnalyzed,   // BB has not been analyzed.
33      ICReAnalyze,     // BB must be re-analyzed.
34      ICNotClassfied,  // BB data valid, but not classified.
35      ICEarlyExit,     // BB is entry of an early-exit sub-CFG.
36      ICTriangle,      // BB is entry of a triangle sub-CFG.
37      ICDiamond,       // BB is entry of a diamond sub-CFG.
38      ICChild,         // BB is part of the sub-CFG that'll be predicated.
39      ICDead           // BB has been converted and merged, it's now dead.
40    };
41
42    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
43    /// if-conversion feasibility analysis. This includes results from
44    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
45    /// classification, and common tail block of its successors (if it's a
46    /// diamond shape), its size, whether it's predicable, and whether any
47    /// instruction can clobber the 'would-be' predicate.
48    ///
49    /// Kind            - Type of block. See BBICKind.
50    /// NonPredSize     - Number of non-predicated instructions.
51    /// isPredicable    - Is it predicable. (FIXME: Remove.)
52    /// hasEarlyExit    - Ends with a return, indirect jump or br to jumptable.
53    /// ModifyPredicate - FIXME: Not used right now. True if BB would modify
54    ///                   the predicate (e.g. has cmp, call, etc.)
55    /// BB              - Corresponding MachineBasicBlock.
56    /// TrueBB / FalseBB- See AnalyzeBranch().
57    /// BrCond          - Conditions for end of block conditional branches.
58    /// Predicate       - Predicate used in the BB.
59    struct BBInfo {
60      BBICKind Kind;
61      unsigned NonPredSize;
62      bool isPredicable;
63      bool hasEarlyExit;
64      bool ModifyPredicate;
65      MachineBasicBlock *BB;
66      MachineBasicBlock *TrueBB;
67      MachineBasicBlock *FalseBB;
68      MachineBasicBlock *TailBB;
69      std::vector<MachineOperand> BrCond;
70      std::vector<MachineOperand> Predicate;
71      BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0), isPredicable(false),
72                 hasEarlyExit(false), ModifyPredicate(false),
73                 BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
74    };
75
76    /// Roots - Basic blocks that do not have successors. These are the starting
77    /// points of Graph traversal.
78    std::vector<MachineBasicBlock*> Roots;
79
80    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
81    /// basic block number.
82    std::vector<BBInfo> BBAnalysis;
83
84    const TargetLowering *TLI;
85    const TargetInstrInfo *TII;
86    bool MadeChange;
87  public:
88    static char ID;
89    IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
90
91    virtual bool runOnMachineFunction(MachineFunction &MF);
92    virtual const char *getPassName() const { return "If converter"; }
93
94  private:
95    void StructuralAnalysis(MachineBasicBlock *BB);
96    void FeasibilityAnalysis(BBInfo &BBI,
97                             std::vector<MachineOperand> &Cond);
98    bool AttemptRestructuring(BBInfo &BBI);
99    bool AnalyzeBlocks(MachineFunction &MF,
100                       std::vector<BBInfo*> &Candidates);
101    void ReTryPreds(MachineBasicBlock *BB);
102    bool IfConvertEarlyExit(BBInfo &BBI);
103    bool IfConvertTriangle(BBInfo &BBI);
104    bool IfConvertDiamond(BBInfo &BBI);
105    void PredicateBlock(BBInfo &BBI,
106                        std::vector<MachineOperand> &Cond,
107                        bool IgnoreTerm = false);
108    void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
109
110    // IfcvtCandidateCmp - Used to sort if-conversion candidates.
111    static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
112      // Favor diamond over triangle, etc.
113      return (unsigned)C1->Kind < (unsigned)C2->Kind;
114    }
115  };
116  char IfConverter::ID = 0;
117}
118
119FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
120
121bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
122  TLI = MF.getTarget().getTargetLowering();
123  TII = MF.getTarget().getInstrInfo();
124  if (!TII) return false;
125
126  DOUT << "\nIfcvt: function \'" << MF.getFunction()->getName() << "\'\n";
127
128  MF.RenumberBlocks();
129  BBAnalysis.resize(MF.getNumBlockIDs());
130
131  // Look for root nodes, i.e. blocks without successors.
132  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
133    if (I->succ_size() == 0)
134      Roots.push_back(I);
135
136  std::vector<BBInfo*> Candidates;
137  MadeChange = false;
138  while (true) {
139    bool Change = false;
140
141    // Do an intial analysis for each basic block and finding all the potential
142    // candidates to perform if-convesion.
143    Change |= AnalyzeBlocks(MF, Candidates);
144    while (!Candidates.empty()) {
145      BBInfo &BBI = *Candidates.back();
146      Candidates.pop_back();
147      switch (BBI.Kind) {
148      default: assert(false && "Unexpected!");
149        break;
150      case ICReAnalyze:
151        // One or more of 'childrean' have been modified, abort!
152        break;
153      case ICEarlyExit:
154        DOUT << "Ifcvt (Early exit): BB#" << BBI.BB->getNumber() << "\n";
155        Change |= IfConvertEarlyExit(BBI);
156        break;
157      case ICTriangle:
158        DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << "\n";
159        Change |= IfConvertTriangle(BBI);
160        break;
161      case ICDiamond:
162        DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << "\n";
163        Change |= IfConvertDiamond(BBI);
164        break;
165      }
166    }
167
168    MadeChange |= Change;
169    if (!Change)
170      break;
171  }
172
173  Roots.clear();
174  BBAnalysis.clear();
175
176  return MadeChange;
177}
178
179static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
180                                         MachineBasicBlock *TrueBB) {
181  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
182         E = BB->succ_end(); SI != E; ++SI) {
183    MachineBasicBlock *SuccBB = *SI;
184    if (SuccBB != TrueBB)
185      return SuccBB;
186  }
187  return NULL;
188}
189
190/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
191/// the specified block. Record its successors and whether it looks like an
192/// if-conversion candidate.
193void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
194  BBInfo &BBI = BBAnalysis[BB->getNumber()];
195
196  if (BBI.Kind != ICReAnalyze) {
197    if (BBI.Kind != ICNotAnalyzed)
198      return;  // Already analyzed.
199    BBI.BB = BB;
200    BBI.NonPredSize = std::distance(BB->begin(), BB->end());
201  }
202
203  // Look for 'root' of a simple (non-nested) triangle or diamond.
204  BBI.Kind = ICNotClassfied;
205  bool CanAnalyze = !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB,
206                                        BBI.BrCond);
207  // Does it end with a return, indirect jump, or jumptable branch?
208  BBI.hasEarlyExit = TII->BlockHasNoFallThrough(*BB) && !BBI.TrueBB;
209  if (!CanAnalyze || !BBI.TrueBB || BBI.BrCond.size() == 0)
210    return;
211
212  // Not a candidate if 'true' block is going to be if-converted.
213  StructuralAnalysis(BBI.TrueBB);
214  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
215
216  // TODO: Only handle very simple cases for now.
217  if (TrueBBI.FalseBB || TrueBBI.BrCond.size())
218    return;
219
220  // No false branch. This BB must end with a conditional branch and a
221  // fallthrough.
222  if (!BBI.FalseBB)
223    BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
224  assert(BBI.FalseBB && "Expected to find the fallthrough block!");
225
226  // Not a candidate if 'false' block is going to be if-converted.
227  StructuralAnalysis(BBI.FalseBB);
228  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
229
230  // TODO: Only handle very simple cases for now.
231  if (FalseBBI.FalseBB || FalseBBI.BrCond.size())
232    return;
233
234  unsigned TrueNumPreds  = BBI.TrueBB->pred_size();
235  unsigned FalseNumPreds = BBI.FalseBB->pred_size();
236  if ((TrueBBI.hasEarlyExit && TrueNumPreds <= 1) &&
237      !(FalseBBI.hasEarlyExit && FalseNumPreds <=1)) {
238    BBI.Kind = ICEarlyExit;
239    TrueBBI.Kind = ICChild;
240  } else if (!(TrueBBI.hasEarlyExit && TrueNumPreds <= 1) &&
241             (FalseBBI.hasEarlyExit && FalseNumPreds <=1)) {
242    BBI.Kind = ICEarlyExit;
243    FalseBBI.Kind = ICChild;
244  } else if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB) {
245    // Triangle:
246    //   EBB
247    //   | \_
248    //   |  |
249    //   | TBB
250    //   |  /
251    //   FBB
252    BBI.Kind = ICTriangle;
253    TrueBBI.Kind = FalseBBI.Kind = ICChild;
254  } else if (TrueBBI.TrueBB == FalseBBI.TrueBB &&
255             TrueNumPreds <= 1 && FalseNumPreds <= 1) {
256    // Diamond:
257    //   EBB
258    //   / \_
259    //  |   |
260    // TBB FBB
261    //   \ /
262    //  TailBB
263    // Note MBB can be empty in case both TBB and FBB are return blocks.
264    BBI.Kind = ICDiamond;
265    TrueBBI.Kind = FalseBBI.Kind = ICChild;
266    BBI.TailBB = TrueBBI.TrueBB;
267  }
268  return;
269}
270
271/// FeasibilityAnalysis - Determine if the block is predicable. In most
272/// cases, that means all the instructions in the block has M_PREDICABLE flag.
273/// Also checks if the block contains any instruction which can clobber a
274/// predicate (e.g. condition code register). If so, the block is not
275/// predicable unless it's the last instruction. Note, this function assumes
276/// all the terminator instructions can be converted or deleted so it ignore
277/// them.
278void IfConverter::FeasibilityAnalysis(BBInfo &BBI,
279                                      std::vector<MachineOperand> &Cond) {
280  if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
281    return;
282
283  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
284       I != E; ++I) {
285    // TODO: check if instruction clobbers predicate.
286    if (TII->isTerminatorInstr(I->getOpcode()))
287      break;
288    if (!I->isPredicable())
289      return;
290  }
291
292  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
293    return;
294
295  BBI.isPredicable = true;
296}
297
298/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
299/// expose more if-conversion opportunities. e.g.
300///
301///                cmp
302///                b le BB1
303///                /  \____
304///               /        |
305///             cmp        |
306///             b eq BB1   |
307///              /  \____  |
308///             /        \ |
309///                      BB1
310///  ==>
311///
312///                cmp
313///                b eq BB1
314///                /  \____
315///               /        |
316///             cmp        |
317///             b le BB1   |
318///              /  \____  |
319///             /        \ |
320///                      BB1
321bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
322  return false;
323}
324
325/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
326/// candidates. It returns true if any CFG restructuring is done to expose more
327/// if-conversion opportunities.
328bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
329                                std::vector<BBInfo*> &Candidates) {
330  bool Change = false;
331  std::set<MachineBasicBlock*> Visited;
332  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
333    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
334           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
335      MachineBasicBlock *BB = *I;
336      StructuralAnalysis(BB);
337      BBInfo &BBI = BBAnalysis[BB->getNumber()];
338      switch (BBI.Kind) {
339        case ICEarlyExit:
340        case ICTriangle:
341        case ICDiamond:
342          Candidates.push_back(&BBI);
343          break;
344        default:
345          Change |= AttemptRestructuring(BBI);
346          break;
347      }
348    }
349  }
350
351  // Sort to favor more complex ifcvt scheme.
352  std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
353
354  return Change;
355}
356
357/// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
358///
359static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
360   std::vector<MachineBasicBlock*> Preds(FromBB->pred_begin(),
361                                         FromBB->pred_end());
362    for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
363      MachineBasicBlock *Pred = Preds[i];
364      Pred->removeSuccessor(FromBB);
365      if (!Pred->isSuccessor(ToBB))
366        Pred->addSuccessor(ToBB);
367    }
368}
369
370/// TransferSuccs - Transfer all the successors of FromBB to ToBB.
371///
372static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
373   std::vector<MachineBasicBlock*> Succs(FromBB->succ_begin(),
374                                         FromBB->succ_end());
375    for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
376      MachineBasicBlock *Succ = Succs[i];
377      FromBB->removeSuccessor(Succ);
378      if (!ToBB->isSuccessor(Succ))
379        ToBB->addSuccessor(Succ);
380    }
381}
382
383/// isNextBlock - Returns true if ToBB the next basic block after BB.
384///
385static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
386  MachineFunction::iterator Fallthrough = BB;
387  return MachineFunction::iterator(ToBB) == ++Fallthrough;
388}
389
390/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
391/// to determine if it can be if-converted.
392void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
393  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
394         E = BB->pred_end(); PI != E; ++PI) {
395    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
396    PBBI.Kind = ICReAnalyze;
397  }
398}
399
400/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
401///
402static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
403                               const TargetInstrInfo *TII) {
404  std::vector<MachineOperand> NoCond;
405  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
406}
407
408/// IfConvertEarlyExit - If convert a early exit sub-CFG.
409///
410bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
411  BBI.Kind = ICNotClassfied;
412
413  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
414  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
415  BBInfo *CvtBBI = &TrueBBI;
416  BBInfo *NextBBI = &FalseBBI;
417
418  bool ReserveCond = false;
419  if (TrueBBI.Kind != ICChild) {
420    std::swap(CvtBBI, NextBBI);
421    ReserveCond = true;
422  }
423
424  std::vector<MachineOperand> NewCond(BBI.BrCond);
425  if (ReserveCond)
426    TII->ReverseBranchCondition(NewCond);
427  FeasibilityAnalysis(*CvtBBI, NewCond);
428  if (!CvtBBI->isPredicable)
429    return false;
430
431  PredicateBlock(*CvtBBI, NewCond);
432
433  // Merge converted block into entry block. Also convert the end of the
434  // block conditional branch (to the non-converted block) into an
435  // unconditional one.
436  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
437  MergeBlocks(BBI, *CvtBBI);
438  if (!isNextBlock(BBI.BB, NextBBI->BB))
439    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
440  std::copy(NewCond.begin(), NewCond.end(), std::back_inserter(BBI.Predicate));
441
442  // Update block info. BB can be iteratively if-converted.
443  BBI.Kind = ICNotAnalyzed;
444  BBI.TrueBB = BBI.FalseBB = NULL;
445  BBI.BrCond.clear();
446  TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
447  ReTryPreds(BBI.BB);
448  CvtBBI->Kind = ICDead;
449
450  // FIXME: Must maintain LiveIns.
451  NumIfConvBBs++;
452  return true;
453}
454
455/// IfConvertTriangle - If convert a triangle sub-CFG.
456///
457bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
458  BBI.Kind = ICNotClassfied;
459
460  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
461  FeasibilityAnalysis(TrueBBI, BBI.BrCond);
462  if (!TrueBBI.isPredicable)
463    return false;
464
465  // Predicate the 'true' block after removing its branch.
466  TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
467  PredicateBlock(TrueBBI, BBI.BrCond);
468
469  // Join the 'true' and 'false' blocks by copying the instructions
470  // from the 'false' block to the 'true' block.
471  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
472  MergeBlocks(TrueBBI, FalseBBI);
473
474  // Now merge the entry of the triangle with the true block.
475  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
476  MergeBlocks(BBI, TrueBBI);
477  std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
478            std::back_inserter(BBI.Predicate));
479
480  // Update block info. BB can be iteratively if-converted.
481  BBI.Kind = ICNotClassfied;
482  BBI.TrueBB = BBI.FalseBB = NULL;
483  BBI.BrCond.clear();
484  TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
485  ReTryPreds(BBI.BB);
486  TrueBBI.Kind = ICDead;
487
488  // FIXME: Must maintain LiveIns.
489  NumIfConvBBs++;
490  return true;
491}
492
493/// IfConvertDiamond - If convert a diamond sub-CFG.
494///
495bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
496  BBI.Kind = ICNotClassfied;
497
498  bool TrueNeedBr;
499  bool FalseNeedBr;
500  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
501  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
502  FeasibilityAnalysis(TrueBBI, BBI.BrCond);
503  std::vector<MachineOperand> RevCond(BBI.BrCond);
504  TII->ReverseBranchCondition(RevCond);
505  FeasibilityAnalysis(FalseBBI, RevCond);
506
507  SmallVector<MachineInstr*, 2> Dups;
508  bool Proceed = TrueBBI.isPredicable && FalseBBI.isPredicable;
509  if (Proceed) {
510    // Check the 'true' and 'false' blocks if either isn't ended with a branch.
511    // Either the block fallthrough to another block or it ends with a
512    // return. If it's the former, add a branch to its successor.
513    TrueNeedBr  = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
514    FalseNeedBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
515    if (TrueNeedBr && TrueBBI.ModifyPredicate) {
516      TrueBBI.isPredicable = false;
517      Proceed = false;
518    }
519    if (FalseNeedBr && FalseBBI.ModifyPredicate) {
520      FalseBBI.isPredicable = false;
521      Proceed = false;
522    }
523
524    if (Proceed) {
525      if (!BBI.TailBB) {
526        // No common merge block. Check if the terminators (e.g. return) are
527        // the same or predicable.
528        MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
529        MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
530        while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
531          if (TT->isIdenticalTo(FT))
532            Dups.push_back(TT);  // Will erase these later.
533          else if (!TT->isPredicable() && !FT->isPredicable()) {
534            Proceed = false;
535            break; // Can't if-convert. Abort!
536          }
537          ++TT;
538          ++FT;
539        }
540
541        // One of the two pathes have more terminators, make sure they are
542        // all predicable.
543        while (Proceed && TT != BBI.TrueBB->end())
544          if (!TT->isPredicable()) {
545            Proceed = false;
546            break; // Can't if-convert. Abort!
547          }
548        while (Proceed && FT != BBI.FalseBB->end())
549          if (!FT->isPredicable()) {
550            Proceed = false;
551            break; // Can't if-convert. Abort!
552          }
553      }
554    }
555  }
556
557  if (!Proceed)
558    return false;
559
560  // Remove the duplicated instructions from the 'true' block.
561  for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
562    Dups[i]->eraseFromParent();
563    --TrueBBI.NonPredSize;
564  }
565
566  // Predicate the 'true' block after removing its branch.
567  TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
568  PredicateBlock(TrueBBI, BBI.BrCond);
569
570  // Predicate the 'false' block.
571  PredicateBlock(FalseBBI, RevCond, true);
572
573  // Merge the 'true' and 'false' blocks by copying the instructions
574  // from the 'false' block to the 'true' block. That is, unless the true
575  // block would clobber the predicate, in that case, do the opposite.
576  BBInfo *CvtBBI;
577  if (!TrueBBI.ModifyPredicate) {
578    // Add a conditional branch from 'true' to 'true' successor if needed.
579    if (TrueNeedBr)
580      TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL,
581                        BBI.BrCond);
582    // Add an unconditional branch from 'false' to to 'false' successor if it
583    // will not be the fallthrough block.
584    if (FalseNeedBr &&
585        !isNextBlock(BBI.BB, *BBI.FalseBB->succ_begin()))
586      InsertUncondBranch(BBI.FalseBB, *BBI.FalseBB->succ_begin(), TII);
587    MergeBlocks(TrueBBI, FalseBBI);
588    CvtBBI = &TrueBBI;
589  } else {
590    // Add a conditional branch from 'false' to 'false' successor if needed.
591    if (FalseNeedBr)
592      TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,
593                        RevCond);
594    // Add an unconditional branch from 'true' to to 'true' successor if it
595    // will not be the fallthrough block.
596    if (TrueNeedBr &&
597        !isNextBlock(BBI.BB, *BBI.TrueBB->succ_begin()))
598      InsertUncondBranch(BBI.TrueBB, *BBI.TrueBB->succ_begin(), TII);
599    MergeBlocks(FalseBBI, TrueBBI);
600    CvtBBI = &FalseBBI;
601  }
602
603  // Remove the conditional branch from entry to the blocks.
604  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
605
606  bool OkToIfcvt = true;
607  // Merge the combined block into the entry of the diamond if the entry
608  // block is its only predecessor. Otherwise, insert an unconditional
609  // branch from entry to the if-converted block.
610  if (CvtBBI->BB->pred_size() == 1) {
611    MergeBlocks(BBI, *CvtBBI);
612    CvtBBI = &BBI;
613    OkToIfcvt = false;
614  } else
615    InsertUncondBranch(BBI.BB, CvtBBI->BB, TII);
616
617  // If the if-converted block fallthrough or unconditionally branch into the
618  // tail block, and the tail block does not have other predecessors, then
619  // fold the tail block in as well.
620  if (BBI.TailBB &&
621      BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
622    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
623    BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
624    MergeBlocks(*CvtBBI, TailBBI);
625    TailBBI.Kind = ICDead;
626  }
627
628  // Update block info. BB may be iteratively if-converted.
629  if (OkToIfcvt) {
630    BBI.Kind = ICNotClassfied;
631    BBI.TrueBB = BBI.FalseBB = NULL;
632    BBI.BrCond.clear();
633    TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
634    ReTryPreds(BBI.BB);
635  }
636  TrueBBI.Kind = ICDead;
637  FalseBBI.Kind = ICDead;
638
639  // FIXME: Must maintain LiveIns.
640  NumIfConvBBs += 2;
641  return true;
642}
643
644/// PredicateBlock - Predicate every instruction in the block with the specified
645/// condition. If IgnoreTerm is true, skip over all terminator instructions.
646void IfConverter::PredicateBlock(BBInfo &BBI,
647                                 std::vector<MachineOperand> &Cond,
648                                 bool IgnoreTerm) {
649  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
650       I != E; ++I) {
651    MachineInstr *MI = I;
652    if (IgnoreTerm && TII->isTerminatorInstr(MI->getOpcode()))
653      continue;
654    if (TII->isPredicated(MI))
655      continue;
656    if (!TII->PredicateInstruction(MI, Cond)) {
657      cerr << "Unable to predication " << *I << "!\n";
658      abort();
659    }
660  }
661
662  BBI.NonPredSize = 0;
663}
664
665/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
666///
667void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
668  ToBBI.BB->splice(ToBBI.BB->end(),
669                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
670
671  // If FromBBI is previously a successor, remove it from ToBBI's successor
672  // list and update its TrueBB / FalseBB field if needed.
673  if (ToBBI.BB->isSuccessor(FromBBI.BB))
674    ToBBI.BB->removeSuccessor(FromBBI.BB);
675
676  // Transfer preds / succs and update size.
677  TransferPreds(ToBBI.BB, FromBBI.BB);
678  TransferSuccs(ToBBI.BB, FromBBI.BB);
679  ToBBI.NonPredSize += FromBBI.NonPredSize;
680  FromBBI.NonPredSize = 0;
681}
682