IfConversion.cpp revision fe57a7e4df512f3a40b8ff463f5362a59908becc 
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 (!I->isPredicable())
287      return;
288  }
289
290  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
291    return;
292
293  BBI.isPredicable = true;
294}
295
296/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
297/// expose more if-conversion opportunities. e.g.
298///
299///                cmp
300///                b le BB1
301///                /  \____
302///               /        |
303///             cmp        |
304///             b eq BB1   |
305///              /  \____  |
306///             /        \ |
307///                      BB1
308///  ==>
309///
310///                cmp
311///                b eq BB1
312///                /  \____
313///               /        |
314///             cmp        |
315///             b le BB1   |
316///              /  \____  |
317///             /        \ |
318///                      BB1
319bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
320  return false;
321}
322
323/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
324/// candidates. It returns true if any CFG restructuring is done to expose more
325/// if-conversion opportunities.
326bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
327                                std::vector<BBInfo*> &Candidates) {
328  bool Change = false;
329  std::set<MachineBasicBlock*> Visited;
330  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
331    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
332           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
333      MachineBasicBlock *BB = *I;
334      StructuralAnalysis(BB);
335      BBInfo &BBI = BBAnalysis[BB->getNumber()];
336      switch (BBI.Kind) {
337        case ICEarlyExit:
338        case ICTriangle:
339        case ICDiamond:
340          Candidates.push_back(&BBI);
341          break;
342        default:
343          Change |= AttemptRestructuring(BBI);
344          break;
345      }
346    }
347  }
348
349  // Sort to favor more complex ifcvt scheme.
350  std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
351
352  return Change;
353}
354
355/// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
356///
357static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
358   std::vector<MachineBasicBlock*> Preds(FromBB->pred_begin(),
359                                         FromBB->pred_end());
360    for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
361      MachineBasicBlock *Pred = Preds[i];
362      Pred->removeSuccessor(FromBB);
363      if (!Pred->isSuccessor(ToBB))
364        Pred->addSuccessor(ToBB);
365    }
366}
367
368/// TransferSuccs - Transfer all the successors of FromBB to ToBB.
369///
370static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
371   std::vector<MachineBasicBlock*> Succs(FromBB->succ_begin(),
372                                         FromBB->succ_end());
373    for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
374      MachineBasicBlock *Succ = Succs[i];
375      FromBB->removeSuccessor(Succ);
376      if (!ToBB->isSuccessor(Succ))
377        ToBB->addSuccessor(Succ);
378    }
379}
380
381/// isNextBlock - Returns true if ToBB the next basic block after BB.
382///
383static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
384  MachineFunction::iterator Fallthrough = BB;
385  return MachineFunction::iterator(ToBB) == ++Fallthrough;
386}
387
388/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
389/// to determine if it can be if-converted.
390void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
391  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
392         E = BB->pred_end(); PI != E; ++PI) {
393    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
394    PBBI.Kind = ICReAnalyze;
395  }
396}
397
398/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
399///
400static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
401                               const TargetInstrInfo *TII) {
402  std::vector<MachineOperand> NoCond;
403  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
404}
405
406/// IfConvertEarlyExit - If convert a early exit sub-CFG.
407///
408bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
409  BBI.Kind = ICNotClassfied;
410
411  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
412  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
413  BBInfo *CvtBBI = &TrueBBI;
414  BBInfo *NextBBI = &FalseBBI;
415
416  bool ReserveCond = false;
417  if (TrueBBI.Kind != ICChild) {
418    std::swap(CvtBBI, NextBBI);
419    ReserveCond = true;
420  }
421
422  std::vector<MachineOperand> NewCond(BBI.BrCond);
423  if (ReserveCond)
424    TII->ReverseBranchCondition(NewCond);
425  FeasibilityAnalysis(*CvtBBI, NewCond);
426  if (!CvtBBI->isPredicable)
427    return false;
428
429  PredicateBlock(*CvtBBI, NewCond);
430
431  // Merge converted block into entry block. Also convert the end of the
432  // block conditional branch (to the non-converted block) into an
433  // unconditional one.
434  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
435  MergeBlocks(BBI, *CvtBBI);
436  if (!isNextBlock(BBI.BB, NextBBI->BB))
437    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
438  std::copy(NewCond.begin(), NewCond.end(), std::back_inserter(BBI.Predicate));
439
440  // Update block info. BB can be iteratively if-converted.
441  BBI.Kind = ICNotAnalyzed;
442  BBI.TrueBB = BBI.FalseBB = NULL;
443  BBI.BrCond.clear();
444  TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
445  ReTryPreds(BBI.BB);
446  CvtBBI->Kind = ICDead;
447
448  // FIXME: Must maintain LiveIns.
449  NumIfConvBBs++;
450  return true;
451}
452
453/// IfConvertTriangle - If convert a triangle sub-CFG.
454///
455bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
456  BBI.Kind = ICNotClassfied;
457
458  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
459  FeasibilityAnalysis(TrueBBI, BBI.BrCond);
460  if (!TrueBBI.isPredicable)
461    return false;
462
463  // Predicate the 'true' block after removing its branch.
464  TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
465  PredicateBlock(TrueBBI, BBI.BrCond);
466
467  // Join the 'true' and 'false' blocks by copying the instructions
468  // from the 'false' block to the 'true' block.
469  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
470  MergeBlocks(TrueBBI, FalseBBI);
471
472  // Now merge the entry of the triangle with the true block.
473  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
474  MergeBlocks(BBI, TrueBBI);
475  std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
476            std::back_inserter(BBI.Predicate));
477
478  // Update block info. BB can be iteratively if-converted.
479  BBI.Kind = ICNotClassfied;
480  BBI.TrueBB = BBI.FalseBB = NULL;
481  BBI.BrCond.clear();
482  TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
483  ReTryPreds(BBI.BB);
484  TrueBBI.Kind = ICDead;
485
486  // FIXME: Must maintain LiveIns.
487  NumIfConvBBs++;
488  return true;
489}
490
491/// IfConvertDiamond - If convert a diamond sub-CFG.
492///
493bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
494  BBI.Kind = ICNotClassfied;
495
496  bool TrueNeedBr;
497  bool FalseNeedBr;
498  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
499  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
500  FeasibilityAnalysis(TrueBBI, BBI.BrCond);
501  std::vector<MachineOperand> RevCond(BBI.BrCond);
502  TII->ReverseBranchCondition(RevCond);
503  FeasibilityAnalysis(FalseBBI, RevCond);
504
505  SmallVector<MachineInstr*, 2> Dups;
506  bool Proceed = TrueBBI.isPredicable && FalseBBI.isPredicable;
507  if (Proceed) {
508    // Check the 'true' and 'false' blocks if either isn't ended with a branch.
509    // Either the block fallthrough to another block or it ends with a
510    // return. If it's the former, add a branch to its successor.
511    TrueNeedBr  = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
512    FalseNeedBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
513    if (TrueNeedBr && TrueBBI.ModifyPredicate) {
514      TrueBBI.isPredicable = false;
515      Proceed = false;
516    }
517    if (FalseNeedBr && FalseBBI.ModifyPredicate) {
518      FalseBBI.isPredicable = false;
519      Proceed = false;
520    }
521
522    if (Proceed) {
523      if (!BBI.TailBB) {
524        // No common merge block. Check if the terminators (e.g. return) are
525        // the same or predicable.
526        MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
527        MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
528        while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
529          if (TT->isIdenticalTo(FT))
530            Dups.push_back(TT);  // Will erase these later.
531          else if (!TT->isPredicable() && !FT->isPredicable()) {
532            Proceed = false;
533            break; // Can't if-convert. Abort!
534          }
535          ++TT;
536          ++FT;
537        }
538
539        // One of the two pathes have more terminators, make sure they are
540        // all predicable.
541        while (Proceed && TT != BBI.TrueBB->end())
542          if (!TT->isPredicable()) {
543            Proceed = false;
544            break; // Can't if-convert. Abort!
545          }
546        while (Proceed && FT != BBI.FalseBB->end())
547          if (!FT->isPredicable()) {
548            Proceed = false;
549            break; // Can't if-convert. Abort!
550          }
551      }
552    }
553  }
554
555  if (!Proceed)
556    return false;
557
558  // Remove the duplicated instructions from the 'true' block.
559  for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
560    Dups[i]->eraseFromParent();
561    --TrueBBI.NonPredSize;
562  }
563
564  // Predicate the 'true' block after removing its branch.
565  TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
566  PredicateBlock(TrueBBI, BBI.BrCond);
567
568  // Predicate the 'false' block.
569  PredicateBlock(FalseBBI, RevCond, true);
570
571  // Merge the 'true' and 'false' blocks by copying the instructions
572  // from the 'false' block to the 'true' block. That is, unless the true
573  // block would clobber the predicate, in that case, do the opposite.
574  BBInfo *CvtBBI;
575  if (!TrueBBI.ModifyPredicate) {
576    // Add a conditional branch from 'true' to 'true' successor if needed.
577    if (TrueNeedBr)
578      TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL,
579                        BBI.BrCond);
580    // Add an unconditional branch from 'false' to to 'false' successor if it
581    // will not be the fallthrough block.
582    if (FalseNeedBr &&
583        !isNextBlock(BBI.BB, *BBI.FalseBB->succ_begin()))
584      InsertUncondBranch(BBI.FalseBB, *BBI.FalseBB->succ_begin(), TII);
585    MergeBlocks(TrueBBI, FalseBBI);
586    CvtBBI = &TrueBBI;
587  } else {
588    // Add a conditional branch from 'false' to 'false' successor if needed.
589    if (FalseNeedBr)
590      TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,
591                        RevCond);
592    // Add an unconditional branch from 'true' to to 'true' successor if it
593    // will not be the fallthrough block.
594    if (TrueNeedBr &&
595        !isNextBlock(BBI.BB, *BBI.TrueBB->succ_begin()))
596      InsertUncondBranch(BBI.TrueBB, *BBI.TrueBB->succ_begin(), TII);
597    MergeBlocks(FalseBBI, TrueBBI);
598    CvtBBI = &FalseBBI;
599  }
600
601  // Remove the conditional branch from entry to the blocks.
602  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
603
604  bool OkToIfcvt = true;
605  // Merge the combined block into the entry of the diamond if the entry
606  // block is its only predecessor. Otherwise, insert an unconditional
607  // branch from entry to the if-converted block.
608  if (CvtBBI->BB->pred_size() == 1) {
609    MergeBlocks(BBI, *CvtBBI);
610    CvtBBI = &BBI;
611    OkToIfcvt = false;
612  } else
613    InsertUncondBranch(BBI.BB, CvtBBI->BB, TII);
614
615  // If the if-converted block fallthrough or unconditionally branch into the
616  // tail block, and the tail block does not have other predecessors, then
617  // fold the tail block in as well.
618  if (BBI.TailBB &&
619      BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
620    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
621    BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
622    MergeBlocks(*CvtBBI, TailBBI);
623    TailBBI.Kind = ICDead;
624  }
625
626  // Update block info. BB may be iteratively if-converted.
627  if (OkToIfcvt) {
628    BBI.Kind = ICNotClassfied;
629    BBI.TrueBB = BBI.FalseBB = NULL;
630    BBI.BrCond.clear();
631    TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
632    ReTryPreds(BBI.BB);
633  }
634  TrueBBI.Kind = ICDead;
635  FalseBBI.Kind = ICDead;
636
637  // FIXME: Must maintain LiveIns.
638  NumIfConvBBs += 2;
639  return true;
640}
641
642/// PredicateBlock - Predicate every instruction in the block with the specified
643/// condition. If IgnoreTerm is true, skip over all terminator instructions.
644void IfConverter::PredicateBlock(BBInfo &BBI,
645                                 std::vector<MachineOperand> &Cond,
646                                 bool IgnoreTerm) {
647  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
648       I != E; ++I) {
649    MachineInstr *MI = I;
650    if (IgnoreTerm && TII->isTerminatorInstr(MI->getOpcode()))
651      continue;
652    if (TII->isPredicated(MI))
653      continue;
654    if (!TII->PredicateInstruction(MI, Cond)) {
655      cerr << "Unable to predicate " << *I << "!\n";
656      abort();
657    }
658  }
659
660  BBI.NonPredSize = 0;
661}
662
663/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
664///
665void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
666  ToBBI.BB->splice(ToBBI.BB->end(),
667                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
668
669  // If FromBBI is previously a successor, remove it from ToBBI's successor
670  // list and update its TrueBB / FalseBB field if needed.
671  if (ToBBI.BB->isSuccessor(FromBBI.BB))
672    ToBBI.BB->removeSuccessor(FromBBI.BB);
673
674  // Transfer preds / succs and update size.
675  TransferPreds(ToBBI.BB, FromBBI.BB);
676  TransferSuccs(ToBBI.BB, FromBBI.BB);
677  ToBBI.NonPredSize += FromBBI.NonPredSize;
678  FromBBI.NonPredSize = 0;
679}
680