1 //===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
3 // The LLVM Compiler Infrastructure
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.
8 //===----------------------------------------------------------------------===//
10 // This file implements the machine instruction level if-conversion pass.
12 //===----------------------------------------------------------------------===//
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"
27 STATISTIC(NumSimple, "Number of simple if-conversions performed");
28 STATISTIC(NumSimpleRev, "Number of simple (reversed) if-conversions performed");
29 STATISTIC(NumTriangle, "Number of triangle if-conversions performed");
30 STATISTIC(NumDiamonds, "Number of diamond if-conversions performed");
31 STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
34 class IfConverter : public MachineFunctionPass {
36 ICNotAnalyzed, // BB has not been analyzed.
37 ICReAnalyze, // BB must be re-analyzed.
38 ICNotClassfied, // BB data valid, but not classified.
39 ICSimple, // BB is entry of an one split, no rejoin sub-CFG.
40 ICSimpleFalse, // Same as ICSimple, but on the false path.
41 ICTriangle, // BB is entry of a triangle sub-CFG.
42 ICDiamond, // BB is entry of a diamond sub-CFG.
43 ICChild, // BB is part of the sub-CFG that'll be predicated.
44 ICDead // BB has been converted and merged, it's now dead.
47 /// BBInfo - One per MachineBasicBlock, this is used to cache the result
48 /// if-conversion feasibility analysis. This includes results from
49 /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
50 /// classification, and common tail block of its successors (if it's a
51 /// diamond shape), its size, whether it's predicable, and whether any
52 /// instruction can clobber the 'would-be' predicate.
54 /// Kind - Type of block. See BBICKind.
55 /// NonPredSize - Number of non-predicated instructions.
56 /// IsAnalyzable - True if AnalyzeBranch() returns false.
57 /// ModifyPredicate - FIXME: Not used right now. True if BB would modify
58 /// the predicate (e.g. has cmp, call, etc.)
59 /// BB - Corresponding MachineBasicBlock.
60 /// TrueBB / FalseBB- See AnalyzeBranch().
61 /// BrCond - Conditions for end of block conditional branches.
62 /// Predicate - Predicate used in the BB.
68 MachineBasicBlock *BB;
69 MachineBasicBlock *TrueBB;
70 MachineBasicBlock *FalseBB;
71 MachineBasicBlock *TailBB;
72 std::vector<MachineOperand> BrCond;
73 std::vector<MachineOperand> Predicate;
74 BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0),
75 IsAnalyzable(false), ModifyPredicate(false),
76 BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
79 /// Roots - Basic blocks that do not have successors. These are the starting
80 /// points of Graph traversal.
81 std::vector<MachineBasicBlock*> Roots;
83 /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
84 /// basic block number.
85 std::vector<BBInfo> BBAnalysis;
87 const TargetLowering *TLI;
88 const TargetInstrInfo *TII;
92 IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
94 virtual bool runOnMachineFunction(MachineFunction &MF);
95 virtual const char *getPassName() const { return "If converter"; }
98 bool ReverseBranchCondition(BBInfo &BBI);
99 void StructuralAnalysis(MachineBasicBlock *BB);
100 bool FeasibilityAnalysis(BBInfo &BBI,
101 std::vector<MachineOperand> &Cond,
102 bool IgnoreTerm = false);
103 bool AttemptRestructuring(BBInfo &BBI);
104 bool AnalyzeBlocks(MachineFunction &MF,
105 std::vector<BBInfo*> &Candidates);
106 void ReTryPreds(MachineBasicBlock *BB);
107 bool IfConvertSimple(BBInfo &BBI);
108 bool IfConvertTriangle(BBInfo &BBI);
109 bool IfConvertDiamond(BBInfo &BBI);
110 void PredicateBlock(BBInfo &BBI,
111 std::vector<MachineOperand> &Cond,
112 bool IgnoreTerm = false);
113 void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
115 // IfcvtCandidateCmp - Used to sort if-conversion candidates.
116 static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
117 // Favor diamond over triangle, etc.
118 return (unsigned)C1->Kind < (unsigned)C2->Kind;
121 char IfConverter::ID = 0;
124 FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
126 bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
127 TLI = MF.getTarget().getTargetLowering();
128 TII = MF.getTarget().getInstrInfo();
129 if (!TII) return false;
131 DOUT << "\nIfcvt: function \'" << MF.getFunction()->getName() << "\'\n";
134 BBAnalysis.resize(MF.getNumBlockIDs());
136 // Look for root nodes, i.e. blocks without successors.
137 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
138 if (I->succ_size() == 0)
141 std::vector<BBInfo*> Candidates;
144 // Do an intial analysis for each basic block and finding all the potential
145 // candidates to perform if-convesion.
146 bool Change = AnalyzeBlocks(MF, Candidates);
147 while (!Candidates.empty()) {
148 BBInfo &BBI = *Candidates.back();
149 Candidates.pop_back();
153 default: assert(false && "Unexpected!");
156 // One or more of 'children' have been modified, abort!
158 // Block has been already been if-converted, abort!
162 DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
163 << "): BB#" << BBI.BB->getNumber() << " ";
164 RetVal = IfConvertSimple(BBI);
165 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
167 if (BBI.Kind == ICSimple) NumSimple++;
171 DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << " ";
172 RetVal = IfConvertTriangle(BBI);
173 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
174 if (RetVal) NumTriangle++;
177 DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " ";
178 RetVal = IfConvertDiamond(BBI);
179 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
180 if (RetVal) NumDiamonds++;
188 MadeChange |= Change;
197 static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
198 MachineBasicBlock *TrueBB) {
199 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
200 E = BB->succ_end(); SI != E; ++SI) {
201 MachineBasicBlock *SuccBB = *SI;
202 if (SuccBB != TrueBB)
208 bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
209 if (!TII->ReverseBranchCondition(BBI.BrCond)) {
210 TII->RemoveBranch(*BBI.BB);
211 TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
212 std::swap(BBI.TrueBB, BBI.FalseBB);
218 /// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
219 /// the specified block. Record its successors and whether it looks like an
220 /// if-conversion candidate.
221 void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
222 BBInfo &BBI = BBAnalysis[BB->getNumber()];
224 if (BBI.Kind == ICReAnalyze) {
226 BBI.TrueBB = BBI.FalseBB = NULL;
228 if (BBI.Kind != ICNotAnalyzed)
229 return; // Already analyzed.
231 BBI.NonPredSize = std::distance(BB->begin(), BB->end());
234 // Look for 'root' of a simple (non-nested) triangle or diamond.
235 BBI.Kind = ICNotClassfied;
237 !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
238 if (!BBI.IsAnalyzable || BBI.BrCond.size() == 0)
240 // Do not ifcvt if either path is a back edge to the entry block.
241 if (BBI.TrueBB == BB || BBI.FalseBB == BB)
244 StructuralAnalysis(BBI.TrueBB);
245 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
247 // No false branch. This BB must end with a conditional branch and a
250 BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
251 assert(BBI.FalseBB && "Expected to find the fallthrough block!");
253 StructuralAnalysis(BBI.FalseBB);
254 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
256 // Look for more opportunities to if-convert a triangle. Try to restructure
257 // the CFG to form a triangle with the 'false' path.
258 std::vector<MachineOperand> RevCond(BBI.BrCond);
259 bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
260 if (FalseBBI.FalseBB) {
261 if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB)
263 std::vector<MachineOperand> Cond(BBI.BrCond);
265 FalseBBI.TrueBB && FalseBBI.BB->pred_size() == 1 &&
266 FeasibilityAnalysis(FalseBBI, RevCond, true)) {
267 std::vector<MachineOperand> FalseCond(FalseBBI.BrCond);
268 if (FalseBBI.TrueBB == BBI.TrueBB &&
269 TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
270 // Reverse 'true' and 'false' paths.
271 ReverseBranchCondition(BBI);
272 BBI.Kind = ICTriangle;
273 FalseBBI.Kind = ICChild;
274 } else if (FalseBBI.FalseBB == BBI.TrueBB &&
275 !TII->ReverseBranchCondition(FalseCond) &&
276 TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
277 // Reverse 'false' block's 'true' and 'false' paths and then
278 // reverse 'true' and 'false' paths.
279 ReverseBranchCondition(FalseBBI);
280 ReverseBranchCondition(BBI);
281 BBI.Kind = ICTriangle;
282 FalseBBI.Kind = ICChild;
285 } else if (TrueBBI.TrueBB == FalseBBI.TrueBB && CanRevCond &&
286 TrueBBI.BB->pred_size() == 1 &&
287 FalseBBI.BB->pred_size() == 1 &&
288 // Check the 'true' and 'false' blocks if either isn't ended with
289 // a branch. If the block does not fallthrough to another block
290 // then we need to add a branch to its successor.
291 !(TrueBBI.ModifyPredicate &&
292 !TrueBBI.TrueBB && TrueBBI.BB->succ_size()) &&
293 !(FalseBBI.ModifyPredicate &&
294 !FalseBBI.TrueBB && FalseBBI.BB->succ_size()) &&
295 FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
296 FeasibilityAnalysis(FalseBBI, RevCond)) {
304 // Note TailBB can be empty.
305 BBI.Kind = ICDiamond;
306 TrueBBI.Kind = FalseBBI.Kind = ICChild;
307 BBI.TailBB = TrueBBI.TrueBB;
309 // FIXME: Consider duplicating if BB is small.
310 bool TryTriangle = TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB &&
311 BBI.TrueBB->pred_size() == 1;
312 bool TrySimple = TrueBBI.BrCond.size() == 0 && BBI.TrueBB->pred_size() == 1;
313 if ((TryTriangle || TrySimple) &&
314 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
323 BBI.Kind = ICTriangle;
324 TrueBBI.Kind = ICChild;
326 // Simple (split, no rejoin):
334 TrueBBI.Kind = ICChild;
336 } else if (FalseBBI.BrCond.size() == 0 && BBI.FalseBB->pred_size() == 1) {
337 // Try 'simple' on the other path...
338 std::vector<MachineOperand> RevCond(BBI.BrCond);
339 if (TII->ReverseBranchCondition(RevCond))
340 assert(false && "Unable to reverse branch condition!");
341 if (FeasibilityAnalysis(FalseBBI, RevCond)) {
342 BBI.Kind = ICSimpleFalse;
343 FalseBBI.Kind = ICChild;
350 /// FeasibilityAnalysis - Determine if the block is predicable. In most
351 /// cases, that means all the instructions in the block has M_PREDICABLE flag.
352 /// Also checks if the block contains any instruction which can clobber a
353 /// predicate (e.g. condition code register). If so, the block is not
354 /// predicable unless it's the last instruction. If IgnoreTerm is true then
355 /// all the terminator instructions are skipped.
356 bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
357 std::vector<MachineOperand> &Cond,
359 // If the block is dead, or it is going to be the entry block of a sub-CFG
360 // that will be if-converted, then it cannot be predicated.
361 if (BBI.Kind != ICNotAnalyzed &&
362 BBI.Kind != ICNotClassfied &&
366 // Check predication threshold.
367 if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
370 // If it is already predicated, check if its predicate subsumes the new
372 if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
375 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
377 if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
379 // TODO: check if instruction clobbers predicate.
380 if (!I->isPredicable())
387 /// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
388 /// expose more if-conversion opportunities. e.g.
410 bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
414 /// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
415 /// candidates. It returns true if any CFG restructuring is done to expose more
416 /// if-conversion opportunities.
417 bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
418 std::vector<BBInfo*> &Candidates) {
420 std::set<MachineBasicBlock*> Visited;
421 for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
422 for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
423 E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
424 MachineBasicBlock *BB = *I;
425 StructuralAnalysis(BB);
426 BBInfo &BBI = BBAnalysis[BB->getNumber()];
432 Candidates.push_back(&BBI);
435 Change |= AttemptRestructuring(BBI);
441 // Sort to favor more complex ifcvt scheme.
442 std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
447 /// isNextBlock - Returns true either if ToBB the next block after BB or
448 /// that all the intervening blocks are empty.
449 static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
450 MachineFunction::iterator I = BB;
451 MachineFunction::iterator TI = ToBB;
452 MachineFunction::iterator E = BB->getParent()->end();
454 if (I == E || !I->empty())
459 /// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
460 /// to determine if it can be if-converted.
461 void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
462 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
463 E = BB->pred_end(); PI != E; ++PI) {
464 BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
465 PBBI.Kind = ICReAnalyze;
469 /// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
471 static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
472 const TargetInstrInfo *TII) {
473 std::vector<MachineOperand> NoCond;
474 TII->InsertBranch(*BB, ToBB, NULL, NoCond);
477 /// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
479 bool IfConverter::IfConvertSimple(BBInfo &BBI) {
480 bool ReverseCond = BBI.Kind == ICSimpleFalse;
482 BBI.Kind = ICNotClassfied;
484 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
485 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
486 BBInfo *CvtBBI = &TrueBBI;
487 BBInfo *NextBBI = &FalseBBI;
489 std::vector<MachineOperand> Cond(BBI.BrCond);
491 std::swap(CvtBBI, NextBBI);
492 TII->ReverseBranchCondition(Cond);
495 PredicateBlock(*CvtBBI, Cond);
496 // If the 'true' block ends without a branch, add a conditional branch
497 // to its successor unless that happens to be the 'false' block.
498 if (CvtBBI->IsAnalyzable && CvtBBI->TrueBB == NULL) {
499 assert(CvtBBI->BB->succ_size() == 1 && "Unexpected!");
500 MachineBasicBlock *SuccBB = *CvtBBI->BB->succ_begin();
501 if (SuccBB != NextBBI->BB)
502 TII->InsertBranch(*CvtBBI->BB, SuccBB, NULL, Cond);
505 // Merge converted block into entry block. Also add an unconditional branch
506 // to the 'false' branch.
507 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
508 MergeBlocks(BBI, *CvtBBI);
509 if (!isNextBlock(BBI.BB, NextBBI->BB))
510 InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
511 std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
513 // Update block info. BB can be iteratively if-converted.
514 BBI.Kind = ICReAnalyze;
516 CvtBBI->Kind = ICDead;
518 // FIXME: Must maintain LiveIns.
522 /// IfConvertTriangle - If convert a triangle sub-CFG.
524 bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
525 BBI.Kind = ICNotClassfied;
527 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
529 // Predicate the 'true' block after removing its branch.
530 TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
531 PredicateBlock(TrueBBI, BBI.BrCond);
533 // If 'true' block has a 'false' successor, add an exit branch to it.
534 bool HasEarlyExit = TrueBBI.FalseBB != NULL;
536 std::vector<MachineOperand> RevCond(TrueBBI.BrCond);
537 if (TII->ReverseBranchCondition(RevCond))
538 assert(false && "Unable to reverse branch condition!");
539 TII->InsertBranch(*BBI.TrueBB, TrueBBI.FalseBB, NULL, RevCond);
542 // Join the 'true' and 'false' blocks if the 'false' block has no other
543 // predecessors. Otherwise, add a unconditional branch from 'true' to 'false'.
544 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
545 bool FalseBBDead = false;
546 if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
547 MergeBlocks(TrueBBI, FalseBBI);
549 } else if (!isNextBlock(TrueBBI.BB, FalseBBI.BB))
550 InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
552 // Now merge the entry of the triangle with the true block.
553 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
554 MergeBlocks(BBI, TrueBBI);
555 std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
556 std::back_inserter(BBI.Predicate));
558 // Update block info. BB can be iteratively if-converted.
559 BBI.Kind = ICReAnalyze;
561 TrueBBI.Kind = ICDead;
563 FalseBBI.Kind = ICDead;
565 // FIXME: Must maintain LiveIns.
569 /// IfConvertDiamond - If convert a diamond sub-CFG.
571 bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
572 BBI.Kind = ICNotClassfied;
574 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
575 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
577 SmallVector<MachineInstr*, 2> Dups;
579 // No common merge block. Check if the terminators (e.g. return) are
580 // the same or predicable.
581 MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
582 MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
583 while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
584 if (TT->isIdenticalTo(FT))
585 Dups.push_back(TT); // Will erase these later.
586 else if (!TT->isPredicable() && !FT->isPredicable())
587 return false; // Can't if-convert. Abort!
592 // One of the two pathes have more terminators, make sure they are
594 while (TT != BBI.TrueBB->end()) {
595 if (!TT->isPredicable()) {
596 return false; // Can't if-convert. Abort!
600 while (FT != BBI.FalseBB->end()) {
601 if (!FT->isPredicable()) {
602 return false; // Can't if-convert. Abort!
608 // Remove the duplicated instructions from the 'true' block.
609 for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
610 Dups[i]->eraseFromParent();
611 --TrueBBI.NonPredSize;
614 // Merge the 'true' and 'false' blocks by copying the instructions
615 // from the 'false' block to the 'true' block. That is, unless the true
616 // block would clobber the predicate, in that case, do the opposite.
617 BBInfo *BBI1 = &TrueBBI;
618 BBInfo *BBI2 = &FalseBBI;
619 std::vector<MachineOperand> RevCond(BBI.BrCond);
620 TII->ReverseBranchCondition(RevCond);
621 std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
622 std::vector<MachineOperand> *Cond2 = &RevCond;
623 if (TrueBBI.ModifyPredicate) {
624 std::swap(BBI1, BBI2);
625 std::swap(Cond1, Cond2);
628 // Check the 'true' and 'false' blocks if either isn't ended with a branch.
629 // Either the block fallthrough to another block or it ends with a
630 // return. If it's the former, add a branch to its successor.
631 bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size();
632 bool NeedBr2 = !BBI2->TrueBB && BBI1->BB->succ_size();
634 // Predicate the 'true' block after removing its branch.
635 BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
636 PredicateBlock(*BBI1, *Cond1);
638 // Add an early exit branch if needed.
640 TII->InsertBranch(*BBI1->BB, *BBI1->BB->succ_begin(), NULL, *Cond1);
642 // Predicate the 'false' block.
643 PredicateBlock(*BBI2, *Cond2, true);
645 // Add an unconditional branch from 'false' to to 'false' successor if it
646 // will not be the fallthrough block.
647 if (NeedBr2 && !isNextBlock(BBI2->BB, *BBI2->BB->succ_begin()))
648 InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII);
650 // Keep them as two separate blocks if there is an early exit.
652 MergeBlocks(*BBI1, *BBI2);
653 else if (!isNextBlock(BBI1->BB, BBI2->BB))
654 InsertUncondBranch(BBI1->BB, BBI2->BB, TII);
656 // Remove the conditional branch from entry to the blocks.
657 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
659 // Merge the combined block into the entry of the diamond.
660 MergeBlocks(BBI, *BBI1);
662 // If the if-converted block fallthrough or unconditionally branch into the
663 // tail block, and the tail block does not have other predecessors, then
664 // fold the tail block in as well.
665 BBInfo *CvtBBI = NeedBr1 ? BBI2 : &BBI;
667 BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
668 CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
669 BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
670 MergeBlocks(*CvtBBI, TailBBI);
671 TailBBI.Kind = ICDead;
674 // Update block info.
675 TrueBBI.Kind = ICDead;
676 FalseBBI.Kind = ICDead;
678 // FIXME: Must maintain LiveIns.
682 /// PredicateBlock - Predicate every instruction in the block with the specified
683 /// condition. If IgnoreTerm is true, skip over all terminator instructions.
684 void IfConverter::PredicateBlock(BBInfo &BBI,
685 std::vector<MachineOperand> &Cond,
687 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
689 if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
691 if (TII->isPredicated(I))
693 if (!TII->PredicateInstruction(I, Cond)) {
694 cerr << "Unable to predicate " << *I << "!\n";
703 /// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
705 static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
706 for (MachineBasicBlock::pred_iterator I = FromBB->pred_begin(),
707 E = FromBB->pred_end(); I != E; ++I) {
708 MachineBasicBlock *Pred = *I;
709 Pred->removeSuccessor(FromBB);
710 if (!Pred->isSuccessor(ToBB))
711 Pred->addSuccessor(ToBB);
715 /// TransferSuccs - Transfer all the successors of FromBB to ToBB.
717 static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
718 for (MachineBasicBlock::succ_iterator I = FromBB->succ_begin(),
719 E = FromBB->succ_end(); I != E; ++I) {
720 MachineBasicBlock *Succ = *I;
721 FromBB->removeSuccessor(Succ);
722 if (!ToBB->isSuccessor(Succ))
723 ToBB->addSuccessor(Succ);
727 /// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
729 void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
730 ToBBI.BB->splice(ToBBI.BB->end(),
731 FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
733 // If FromBBI is previously a successor, remove it from ToBBI's successor
734 // list and update its TrueBB / FalseBB field if needed.
735 if (ToBBI.BB->isSuccessor(FromBBI.BB))
736 ToBBI.BB->removeSuccessor(FromBBI.BB);
738 // Redirect all branches to FromBB to ToBB.
739 std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
740 FromBBI.BB->pred_end());
741 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
742 Preds[i]->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
744 // Transfer preds / succs and update size.
745 TransferPreds(ToBBI.BB, FromBBI.BB);
746 TransferSuccs(ToBBI.BB, FromBBI.BB);
747 ToBBI.NonPredSize += FromBBI.NonPredSize;
748 FromBBI.NonPredSize = 0;