1 //===- LoopIndexSplit.cpp - Loop Index Splitting Pass ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Devang Patel and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements Loop Index Splitting Pass.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "loop-index-split"
16 #include "llvm/Transforms/Scalar.h"
17 #include "llvm/Analysis/LoopPass.h"
18 #include "llvm/Analysis/ScalarEvolutionExpander.h"
19 #include "llvm/Analysis/Dominators.h"
20 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
21 #include "llvm/Transforms/Utils/Cloning.h"
22 #include "llvm/Support/Compiler.h"
23 #include "llvm/ADT/DepthFirstIterator.h"
24 #include "llvm/ADT/Statistic.h"
28 STATISTIC(NumIndexSplit, "Number of loops index split");
32 class VISIBILITY_HIDDEN LoopIndexSplit : public LoopPass {
35 static char ID; // Pass ID, replacement for typeid
36 LoopIndexSplit() : LoopPass((intptr_t)&ID) {}
38 // Index split Loop L. Return true if loop is split.
39 bool runOnLoop(Loop *L, LPPassManager &LPM);
41 void getAnalysisUsage(AnalysisUsage &AU) const {
42 AU.addRequired<ScalarEvolution>();
43 AU.addPreserved<ScalarEvolution>();
44 AU.addRequiredID(LCSSAID);
45 AU.addPreservedID(LCSSAID);
46 AU.addRequired<LoopInfo>();
47 AU.addPreserved<LoopInfo>();
48 AU.addRequiredID(LoopSimplifyID);
49 AU.addPreservedID(LoopSimplifyID);
50 AU.addRequired<DominatorTree>();
51 AU.addRequired<DominanceFrontier>();
52 AU.addPreserved<DominatorTree>();
53 AU.addPreserved<DominanceFrontier>();
60 SplitInfo() : SplitValue(NULL), SplitCondition(NULL),
61 UseTrueBranchFirst(true), A_ExitValue(NULL),
64 // Induction variable's range is split at this value.
67 // This compare instruction compares IndVar against SplitValue.
68 ICmpInst *SplitCondition;
70 // True if after loop index split, first loop will execute split condition's
72 bool UseTrueBranchFirst;
74 // Exit value for first loop after loop split.
77 // Start value for second loop after loop split.
83 SplitCondition = NULL;
84 UseTrueBranchFirst = true;
92 /// Find condition inside a loop that is suitable candidate for index split.
93 void findSplitCondition();
95 /// Find loop's exit condition.
96 void findLoopConditionals();
98 /// Return induction variable associated with value V.
99 void findIndVar(Value *V, Loop *L);
101 /// processOneIterationLoop - Current loop L contains compare instruction
102 /// that compares induction variable, IndVar, agains loop invariant. If
103 /// entire (i.e. meaningful) loop body is dominated by this compare
104 /// instruction then loop body is executed only for one iteration. In
105 /// such case eliminate loop structure surrounding this loop body. For
106 bool processOneIterationLoop(SplitInfo &SD);
108 /// If loop header includes loop variant instruction operands then
109 /// this loop may not be eliminated.
110 bool safeHeader(SplitInfo &SD, BasicBlock *BB);
112 /// If Exiting block includes loop variant instructions then this
113 /// loop may not be eliminated.
114 bool safeExitingBlock(SplitInfo &SD, BasicBlock *BB);
116 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
117 /// This routine is used to remove split condition's dead branch, dominated by
118 /// DeadBB. LiveBB dominates split conidition's other branch.
119 void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB);
121 /// safeSplitCondition - Return true if it is possible to
122 /// split loop using given split condition.
123 bool safeSplitCondition(SplitInfo &SD);
125 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
126 /// based on split value.
127 void calculateLoopBounds(SplitInfo &SD);
129 /// updatePHINodes - CFG has been changed.
131 /// - ExitBB's single predecessor was Latch
132 /// - Latch's second successor was Header
134 /// - ExitBB's single predecessor was Header
135 /// - Latch's one and only successor was Header
137 /// Update ExitBB PHINodes' to reflect this change.
138 void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
140 PHINode *IV, Instruction *IVIncrement);
142 /// moveExitCondition - Move exit condition EC into split condition block CondBB.
143 void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
144 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
145 PHINode *IV, Instruction *IVAdd, Loop *LP);
147 /// splitLoop - Split current loop L in two loops using split information
148 /// SD. Update dominator information. Maintain LCSSA form.
149 bool splitLoop(SplitInfo &SD);
153 IndVarIncrement = NULL;
154 ExitCondition = NULL;
168 DominanceFrontier *DF;
169 SmallVector<SplitInfo, 4> SplitData;
171 // Induction variable whose range is being split by this transformation.
173 Instruction *IndVarIncrement;
175 // Loop exit condition.
176 ICmpInst *ExitCondition;
178 // Induction variable's initial value.
181 // Induction variable's final loop exit value operand number in exit condition..
182 unsigned ExitValueNum;
185 char LoopIndexSplit::ID = 0;
186 RegisterPass<LoopIndexSplit> X ("loop-index-split", "Index Split Loops");
189 LoopPass *llvm::createLoopIndexSplitPass() {
190 return new LoopIndexSplit();
193 // Index split Loop L. Return true if loop is split.
194 bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
195 bool Changed = false;
199 // FIXME - Nested loops make dominator info updates tricky.
200 if (!L->getSubLoops().empty())
203 SE = &getAnalysis<ScalarEvolution>();
204 DT = &getAnalysis<DominatorTree>();
205 LI = &getAnalysis<LoopInfo>();
206 DF = &getAnalysis<DominanceFrontier>();
210 findLoopConditionals();
215 findSplitCondition();
217 if (SplitData.empty())
220 // First see if it is possible to eliminate loop itself or not.
221 for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin(),
222 E = SplitData.end(); SI != E;) {
224 if (SD.SplitCondition->getPredicate() == ICmpInst::ICMP_EQ) {
225 Changed = processOneIterationLoop(SD);
228 // If is loop is eliminated then nothing else to do here.
231 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
233 SplitData.erase(Delete_SI);
239 if (SplitData.empty())
242 // Split most profitiable condition.
243 // FIXME : Implement cost analysis.
244 unsigned MostProfitableSDIndex = 0;
245 Changed = splitLoop(SplitData[MostProfitableSDIndex]);
253 /// Return true if V is a induction variable or induction variable's
254 /// increment for loop L.
255 void LoopIndexSplit::findIndVar(Value *V, Loop *L) {
257 Instruction *I = dyn_cast<Instruction>(V);
261 // Check if I is a phi node from loop header or not.
262 if (PHINode *PN = dyn_cast<PHINode>(V)) {
263 if (PN->getParent() == L->getHeader()) {
269 // Check if I is a add instruction whose one operand is
270 // phi node from loop header and second operand is constant.
271 if (I->getOpcode() != Instruction::Add)
274 Value *Op0 = I->getOperand(0);
275 Value *Op1 = I->getOperand(1);
277 if (PHINode *PN = dyn_cast<PHINode>(Op0)) {
278 if (PN->getParent() == L->getHeader()
279 && isa<ConstantInt>(Op1)) {
286 if (PHINode *PN = dyn_cast<PHINode>(Op1)) {
287 if (PN->getParent() == L->getHeader()
288 && isa<ConstantInt>(Op0)) {
298 // Find loop's exit condition and associated induction variable.
299 void LoopIndexSplit::findLoopConditionals() {
301 BasicBlock *ExitingBlock = NULL;
303 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
306 if (!L->isLoopExit(BB))
316 // If exiting block is neither loop header nor loop latch then this loop is
318 if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch())
321 // If exit block's terminator is conditional branch inst then we have found
323 BranchInst *BR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
324 if (!BR || BR->isUnconditional())
327 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
332 if (CI->getPredicate() == ICmpInst::ICMP_SGT
333 || CI->getPredicate() == ICmpInst::ICMP_UGT
334 || CI->getPredicate() == ICmpInst::ICMP_SGE
335 || CI->getPredicate() == ICmpInst::ICMP_UGE)
340 // Exit condition's one operand is loop invariant exit value and second
341 // operand is SCEVAddRecExpr based on induction variable.
342 Value *V0 = CI->getOperand(0);
343 Value *V1 = CI->getOperand(1);
345 SCEVHandle SH0 = SE->getSCEV(V0);
346 SCEVHandle SH1 = SE->getSCEV(V1);
348 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
352 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
358 ExitCondition = NULL;
360 BasicBlock *Preheader = L->getLoopPreheader();
361 StartValue = IndVar->getIncomingValueForBlock(Preheader);
365 /// Find condition inside a loop that is suitable candidate for index split.
366 void LoopIndexSplit::findSplitCondition() {
369 // Check all basic block's terminators.
371 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
375 // If this basic block does not terminate in a conditional branch
376 // then terminator is not a suitable split condition.
377 BranchInst *BR = dyn_cast<BranchInst>(BB->getTerminator());
381 if (BR->isUnconditional())
384 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
385 if (!CI || CI == ExitCondition)
388 if (CI->getPredicate() == ICmpInst::ICMP_NE)
391 // If split condition predicate is GT or GE then first execute
392 // false branch of split condition.
393 if (CI->getPredicate() != ICmpInst::ICMP_ULT
394 && CI->getPredicate() != ICmpInst::ICMP_SLT
395 && CI->getPredicate() != ICmpInst::ICMP_ULE
396 && CI->getPredicate() != ICmpInst::ICMP_SLE)
397 SD.UseTrueBranchFirst = false;
399 // If one operand is loop invariant and second operand is SCEVAddRecExpr
400 // based on induction variable then CI is a candidate split condition.
401 Value *V0 = CI->getOperand(0);
402 Value *V1 = CI->getOperand(1);
404 SCEVHandle SH0 = SE->getSCEV(V0);
405 SCEVHandle SH1 = SE->getSCEV(V1);
407 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
409 SD.SplitCondition = CI;
410 if (PHINode *PN = dyn_cast<PHINode>(V1)) {
412 SplitData.push_back(SD);
414 else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
415 if (IndVarIncrement && IndVarIncrement == Insn)
416 SplitData.push_back(SD);
419 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
421 SD.SplitCondition = CI;
422 if (PHINode *PN = dyn_cast<PHINode>(V0)) {
424 SplitData.push_back(SD);
426 else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
427 if (IndVarIncrement && IndVarIncrement == Insn)
428 SplitData.push_back(SD);
434 /// processOneIterationLoop - Current loop L contains compare instruction
435 /// that compares induction variable, IndVar, against loop invariant. If
436 /// entire (i.e. meaningful) loop body is dominated by this compare
437 /// instruction then loop body is executed only once. In such case eliminate
438 /// loop structure surrounding this loop body. For example,
439 /// for (int i = start; i < end; ++i) {
440 /// if ( i == somevalue) {
444 /// can be transformed into
445 /// if (somevalue >= start && somevalue < end) {
449 bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
451 BasicBlock *Header = L->getHeader();
453 // First of all, check if SplitCondition dominates entire loop body
456 // If SplitCondition is not in loop header then this loop is not suitable
457 // for this transformation.
458 if (SD.SplitCondition->getParent() != Header)
461 // If loop header includes loop variant instruction operands then
462 // this loop may not be eliminated.
463 if (!safeHeader(SD, Header))
466 // If Exiting block includes loop variant instructions then this
467 // loop may not be eliminated.
468 if (!safeExitingBlock(SD, ExitCondition->getParent()))
473 // Replace index variable with split value in loop body. Loop body is executed
474 // only when index variable is equal to split value.
475 IndVar->replaceAllUsesWith(SD.SplitValue);
477 // Remove Latch to Header edge.
478 BasicBlock *Latch = L->getLoopLatch();
479 BasicBlock *LatchSucc = NULL;
480 BranchInst *BR = dyn_cast<BranchInst>(Latch->getTerminator());
483 Header->removePredecessor(Latch);
484 for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
489 BR->setUnconditionalDest(LatchSucc);
491 Instruction *Terminator = Header->getTerminator();
492 Value *ExitValue = ExitCondition->getOperand(ExitValueNum);
494 // Replace split condition in header.
496 // SplitCondition : icmp eq i32 IndVar, SplitValue
498 // c1 = icmp uge i32 SplitValue, StartValue
499 // c2 = icmp ult i32 vSplitValue, ExitValue
501 bool SignedPredicate = ExitCondition->isSignedPredicate();
502 Instruction *C1 = new ICmpInst(SignedPredicate ?
503 ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
504 SD.SplitValue, StartValue, "lisplit",
506 Instruction *C2 = new ICmpInst(SignedPredicate ?
507 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
508 SD.SplitValue, ExitValue, "lisplit",
510 Instruction *NSplitCond = BinaryOperator::createAnd(C1, C2, "lisplit",
512 SD.SplitCondition->replaceAllUsesWith(NSplitCond);
513 SD.SplitCondition->eraseFromParent();
515 // Now, clear latch block. Remove instructions that are responsible
516 // to increment induction variable.
517 Instruction *LTerminator = Latch->getTerminator();
518 for (BasicBlock::iterator LB = Latch->begin(), LE = Latch->end();
522 if (isa<PHINode>(I) || I == LTerminator)
525 if (I == IndVarIncrement)
526 I->replaceAllUsesWith(ExitValue);
528 I->replaceAllUsesWith(UndefValue::get(I->getType()));
529 I->eraseFromParent();
532 LPM->deleteLoopFromQueue(L);
534 // Update Dominator Info.
535 // Only CFG change done is to remove Latch to Header edge. This
536 // does not change dominator tree because Latch did not dominate
539 DominanceFrontier::iterator HeaderDF = DF->find(Header);
540 if (HeaderDF != DF->end())
541 DF->removeFromFrontier(HeaderDF, Header);
543 DominanceFrontier::iterator LatchDF = DF->find(Latch);
544 if (LatchDF != DF->end())
545 DF->removeFromFrontier(LatchDF, Header);
550 // If loop header includes loop variant instruction operands then
551 // this loop can not be eliminated. This is used by processOneIterationLoop().
552 bool LoopIndexSplit::safeHeader(SplitInfo &SD, BasicBlock *Header) {
554 Instruction *Terminator = Header->getTerminator();
555 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
563 // SplitCondition itself is OK.
564 if (I == SD.SplitCondition)
567 // Induction variable is OK.
571 // Induction variable increment is OK.
572 if (I == IndVarIncrement)
575 // Terminator is also harmless.
579 // Otherwise we have a instruction that may not be safe.
586 // If Exiting block includes loop variant instructions then this
587 // loop may not be eliminated. This is used by processOneIterationLoop().
588 bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD,
589 BasicBlock *ExitingBlock) {
591 for (BasicBlock::iterator BI = ExitingBlock->begin(),
592 BE = ExitingBlock->end(); BI != BE; ++BI) {
599 // Induction variable increment is OK.
600 if (IndVarIncrement && IndVarIncrement == I)
603 // Check if I is induction variable increment instruction.
604 if (!IndVarIncrement && I->getOpcode() == Instruction::Add) {
606 Value *Op0 = I->getOperand(0);
607 Value *Op1 = I->getOperand(1);
609 ConstantInt *CI = NULL;
611 if ((PN = dyn_cast<PHINode>(Op0))) {
612 if ((CI = dyn_cast<ConstantInt>(Op1)))
615 if ((PN = dyn_cast<PHINode>(Op1))) {
616 if ((CI = dyn_cast<ConstantInt>(Op0)))
620 if (IndVarIncrement && PN == IndVar && CI->isOne())
624 // I is an Exit condition if next instruction is block terminator.
625 // Exit condition is OK if it compares loop invariant exit value,
626 // which is checked below.
627 else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
628 if (EC == ExitCondition)
632 if (I == ExitingBlock->getTerminator())
635 // Otherwise we have instruction that may not be safe.
639 // We could not find any reason to consider ExitingBlock unsafe.
643 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
644 /// This routine is used to remove split condition's dead branch, dominated by
645 /// DeadBB. LiveBB dominates split conidition's other branch.
646 void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
647 BasicBlock *LiveBB) {
649 // First update DeadBB's dominance frontier.
650 SmallVector<BasicBlock *, 8> FrontierBBs;
651 DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
652 if (DeadBBDF != DF->end()) {
653 SmallVector<BasicBlock *, 8> PredBlocks;
655 DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
656 for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
657 DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
658 BasicBlock *FrontierBB = *DeadBBSetI;
659 FrontierBBs.push_back(FrontierBB);
661 // Rremove any PHI incoming edge from blocks dominated by DeadBB.
663 for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
666 if (P == DeadBB || DT->dominates(DeadBB, P))
667 PredBlocks.push_back(P);
670 for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
672 if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
673 for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
674 PE = PredBlocks.end(); PI != PE; ++PI) {
676 PN->removeIncomingValue(P);
685 // Now remove DeadBB and all nodes dominated by DeadBB in df order.
686 SmallVector<BasicBlock *, 32> WorkList;
687 DomTreeNode *DN = DT->getNode(DeadBB);
688 for (df_iterator<DomTreeNode*> DI = df_begin(DN),
689 E = df_end(DN); DI != E; ++DI) {
690 BasicBlock *BB = DI->getBlock();
691 WorkList.push_back(BB);
692 BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
695 while (!WorkList.empty()) {
696 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
697 for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
699 Instruction *I = BBI;
700 I->replaceAllUsesWith(UndefValue::get(I->getType()));
701 I->eraseFromParent();
703 LPM->deleteSimpleAnalysisValue(BB, LP);
707 BB->eraseFromParent();
710 // Update Frontier BBs' dominator info.
711 while (!FrontierBBs.empty()) {
712 BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
713 BasicBlock *NewDominator = FBB->getSinglePredecessor();
715 pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
718 if (NewDominator != LiveBB) {
719 for(; PI != PE; ++PI) {
722 NewDominator = LiveBB;
725 NewDominator = DT->findNearestCommonDominator(NewDominator, P);
729 assert (NewDominator && "Unable to fix dominator info.");
730 DT->changeImmediateDominator(FBB, NewDominator);
731 DF->changeImmediateDominator(FBB, NewDominator, DT);
736 /// safeSplitCondition - Return true if it is possible to
737 /// split loop using given split condition.
738 bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
740 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
742 // Unable to handle triange loops at the moment.
743 // In triangle loop, split condition is in header and one of the
744 // the split destination is loop latch. If split condition is EQ
745 // then such loops are already handle in processOneIterationLoop().
746 BasicBlock *Latch = L->getLoopLatch();
747 BranchInst *SplitTerminator =
748 cast<BranchInst>(SplitCondBlock->getTerminator());
749 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
750 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
751 if (L->getHeader() == SplitCondBlock
752 && (Latch == Succ0 || Latch == Succ1))
755 // If one of the split condition branch is post dominating other then loop
756 // index split is not appropriate.
757 if (DT->dominates(Succ0, Latch) || DT->dominates(Succ1, Latch))
760 // If one of the split condition branch is a predecessor of the other
761 // split condition branch head then do not split loop on this condition.
762 for(pred_iterator PI = pred_begin(Succ0), PE = pred_end(Succ0);
766 for(pred_iterator PI = pred_begin(Succ1), PE = pred_end(Succ1);
771 // Finally this split condition is safe only if merge point for
772 // split condition branch is loop latch. This check along with previous
773 // check, to ensure that exit condition is in either loop latch or header,
774 // filters all loops with non-empty loop body between merge point
775 // and exit condition.
776 DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
777 assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
778 if (Succ0DF->second.count(Latch))
781 DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
782 assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
783 if (Succ1DF->second.count(Latch))
789 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
790 /// based on split value.
791 void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
793 ICmpInst::Predicate SP = SD.SplitCondition->getPredicate();
794 const Type *Ty = SD.SplitValue->getType();
795 bool Sign = ExitCondition->isSignedPredicate();
796 BasicBlock *Preheader = L->getLoopPreheader();
797 Instruction *PHTerminator = Preheader->getTerminator();
799 // Initially use split value as upper loop bound for first loop and lower loop
800 // bound for second loop.
801 Value *AEV = SD.SplitValue;
802 Value *BSV = SD.SplitValue;
804 switch (ExitCondition->getPredicate()) {
805 case ICmpInst::ICMP_SGT:
806 case ICmpInst::ICMP_UGT:
807 case ICmpInst::ICMP_SGE:
808 case ICmpInst::ICMP_UGE:
810 assert (0 && "Unexpected exit condition predicate");
812 case ICmpInst::ICMP_SLT:
813 case ICmpInst::ICMP_ULT:
816 case ICmpInst::ICMP_SLT:
817 case ICmpInst::ICMP_ULT:
819 // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
821 // is transformed into
823 // for (i = LB; i < min(UB, AEV); ++i)
825 // for (i = max(LB, BSV); i < UB; ++i);
828 case ICmpInst::ICMP_SLE:
829 case ICmpInst::ICMP_ULE:
832 // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
834 // is transformed into
838 // for (i = LB; i < min(UB, AEV); ++i)
840 // for (i = max(LB, BSV); i < UB; ++i)
842 BSV = BinaryOperator::createAdd(SD.SplitValue,
843 ConstantInt::get(Ty, 1, Sign),
844 "lsplit.add", PHTerminator);
848 case ICmpInst::ICMP_SGE:
849 case ICmpInst::ICMP_UGE:
851 // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
853 // is transformed into
855 // for (i = LB; i < min(UB, AEV); ++i)
857 // for (i = max(BSV, LB); i < UB; ++i)
860 case ICmpInst::ICMP_SGT:
861 case ICmpInst::ICMP_UGT:
864 // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
866 // is transformed into
868 // BSV = AEV = SV + 1
869 // for (i = LB; i < min(UB, AEV); ++i)
871 // for (i = max(LB, BSV); i < UB; ++i)
873 BSV = BinaryOperator::createAdd(SD.SplitValue,
874 ConstantInt::get(Ty, 1, Sign),
875 "lsplit.add", PHTerminator);
880 assert (0 && "Unexpected split condition predicate");
885 case ICmpInst::ICMP_SLE:
886 case ICmpInst::ICMP_ULE:
889 case ICmpInst::ICMP_SLT:
890 case ICmpInst::ICMP_ULT:
892 // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
894 // is transformed into
897 // for (i = LB; i <= min(UB, AEV); ++i)
899 // for (i = max(LB, BSV); i <= UB; ++i)
901 AEV = BinaryOperator::createSub(SD.SplitValue,
902 ConstantInt::get(Ty, 1, Sign),
903 "lsplit.sub", PHTerminator);
905 case ICmpInst::ICMP_SLE:
906 case ICmpInst::ICMP_ULE:
908 // for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; }
910 // is transformed into
913 // for (i = LB; i <= min(UB, AEV); ++i)
915 // for (i = max(LB, BSV); i <= UB; ++i)
917 BSV = BinaryOperator::createAdd(SD.SplitValue,
918 ConstantInt::get(Ty, 1, Sign),
919 "lsplit.add", PHTerminator);
921 case ICmpInst::ICMP_SGT:
922 case ICmpInst::ICMP_UGT:
924 // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
926 // is transformed into
929 // for (i = LB; i <= min(AEV, UB); ++i)
931 // for (i = max(LB, BSV); i <= UB; ++i)
933 BSV = BinaryOperator::createAdd(SD.SplitValue,
934 ConstantInt::get(Ty, 1, Sign),
935 "lsplit.add", PHTerminator);
937 case ICmpInst::ICMP_SGE:
938 case ICmpInst::ICMP_UGE:
941 // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
943 // is transformed into
946 // for (i = LB; i <= min(AEV, UB); ++i)
948 // for (i = max(LB, BSV); i <= UB; ++i)
950 AEV = BinaryOperator::createSub(SD.SplitValue,
951 ConstantInt::get(Ty, 1, Sign),
952 "lsplit.sub", PHTerminator);
955 assert (0 && "Unexpected split condition predicate");
962 // Calculate ALoop induction variable's new exiting value and
963 // BLoop induction variable's new starting value. Calculuate these
964 // values in original loop's preheader.
965 // A_ExitValue = min(SplitValue, OrignalLoopExitValue)
966 // B_StartValue = max(SplitValue, OriginalLoopStartValue)
967 Value *C1 = new ICmpInst(Sign ?
968 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
970 ExitCondition->getOperand(ExitValueNum),
971 "lsplit.ev", PHTerminator);
972 SD.A_ExitValue = new SelectInst(C1, AEV,
973 ExitCondition->getOperand(ExitValueNum),
974 "lsplit.ev", PHTerminator);
976 Value *C2 = new ICmpInst(Sign ?
977 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
978 BSV, StartValue, "lsplit.sv",
980 SD.B_StartValue = new SelectInst(C2, StartValue, BSV,
981 "lsplit.sv", PHTerminator);
984 /// splitLoop - Split current loop L in two loops using split information
985 /// SD. Update dominator information. Maintain LCSSA form.
986 bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
988 if (!safeSplitCondition(SD))
991 // After loop is cloned there are two loops.
993 // First loop, referred as ALoop, executes first part of loop's iteration
994 // space split. Second loop, referred as BLoop, executes remaining
995 // part of loop's iteration space.
997 // ALoop's exit edge enters BLoop's header through a forwarding block which
998 // acts as a BLoop's preheader.
999 BasicBlock *Preheader = L->getLoopPreheader();
1001 // Calculate ALoop induction variable's new exiting value and
1002 // BLoop induction variable's new starting value.
1003 calculateLoopBounds(SD);
1006 DenseMap<const Value *, Value *> ValueMap;
1007 Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
1009 BasicBlock *B_Header = BLoop->getHeader();
1011 //[*] ALoop's exiting edge BLoop's header.
1012 // ALoop's original exit block becomes BLoop's exit block.
1013 PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
1014 BasicBlock *A_ExitingBlock = ExitCondition->getParent();
1015 BranchInst *A_ExitInsn =
1016 dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
1017 assert (A_ExitInsn && "Unable to find suitable loop exit branch");
1018 BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
1019 if (L->contains(B_ExitBlock)) {
1020 B_ExitBlock = A_ExitInsn->getSuccessor(0);
1021 A_ExitInsn->setSuccessor(0, B_Header);
1023 A_ExitInsn->setSuccessor(1, B_Header);
1025 //[*] Update ALoop's exit value using new exit value.
1026 ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
1028 // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
1029 // original loop's preheader. Add incoming PHINode values from
1030 // ALoop's exiting block. Update BLoop header's domiantor info.
1032 // Collect inverse map of Header PHINodes.
1033 DenseMap<Value *, Value *> InverseMap;
1034 for (BasicBlock::iterator BI = L->getHeader()->begin(),
1035 BE = L->getHeader()->end(); BI != BE; ++BI) {
1036 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1037 PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
1038 InverseMap[PNClone] = PN;
1043 for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1045 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1046 // Remove incoming value from original preheader.
1047 PN->removeIncomingValue(Preheader);
1049 // Add incoming value from A_ExitingBlock.
1051 PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
1053 PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
1054 Value *V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
1055 PN->addIncoming(V2, A_ExitingBlock);
1060 DT->changeImmediateDominator(B_Header, A_ExitingBlock);
1061 DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
1063 // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
1064 // block. Remove incoming PHINode values from ALoop's exiting block.
1065 // Add new incoming values from BLoop's incoming exiting value.
1066 // Update BLoop exit block's dominator info..
1067 BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
1068 for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
1070 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1071 PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
1073 PN->removeIncomingValue(A_ExitingBlock);
1078 DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
1079 DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
1081 //[*] Split ALoop's exit edge. This creates a new block which
1082 // serves two purposes. First one is to hold PHINode defnitions
1083 // to ensure that ALoop's LCSSA form. Second use it to act
1084 // as a preheader for BLoop.
1085 BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
1087 //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
1088 // in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
1089 for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1091 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1092 Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
1093 PHINode *newPHI = new PHINode(PN->getType(), PN->getName());
1094 newPHI->addIncoming(V1, A_ExitingBlock);
1095 A_ExitBlock->getInstList().push_front(newPHI);
1096 PN->removeIncomingValue(A_ExitBlock);
1097 PN->addIncoming(newPHI, A_ExitBlock);
1102 //[*] Eliminate split condition's inactive branch from ALoop.
1103 BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
1104 BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
1105 BasicBlock *A_InactiveBranch = NULL;
1106 BasicBlock *A_ActiveBranch = NULL;
1107 if (SD.UseTrueBranchFirst) {
1108 A_ActiveBranch = A_BR->getSuccessor(0);
1109 A_InactiveBranch = A_BR->getSuccessor(1);
1111 A_ActiveBranch = A_BR->getSuccessor(1);
1112 A_InactiveBranch = A_BR->getSuccessor(0);
1114 A_BR->setUnconditionalDest(A_ActiveBranch);
1115 removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
1117 //[*] Eliminate split condition's inactive branch in from BLoop.
1118 BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
1119 BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
1120 BasicBlock *B_InactiveBranch = NULL;
1121 BasicBlock *B_ActiveBranch = NULL;
1122 if (SD.UseTrueBranchFirst) {
1123 B_ActiveBranch = B_BR->getSuccessor(1);
1124 B_InactiveBranch = B_BR->getSuccessor(0);
1126 B_ActiveBranch = B_BR->getSuccessor(0);
1127 B_InactiveBranch = B_BR->getSuccessor(1);
1129 B_BR->setUnconditionalDest(B_ActiveBranch);
1130 removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
1132 BasicBlock *A_Header = L->getHeader();
1133 if (A_ExitingBlock == A_Header)
1136 //[*] Move exit condition into split condition block to avoid
1137 // executing dead loop iteration.
1138 ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
1139 Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
1140 ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
1142 moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
1143 SD.SplitCondition, IndVar, IndVarIncrement, ALoop);
1145 moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
1146 B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
1151 // moveExitCondition - Move exit condition EC into split condition block CondBB.
1152 void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
1153 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
1154 PHINode *IV, Instruction *IVAdd, Loop *LP) {
1156 BasicBlock *ExitingBB = EC->getParent();
1157 Instruction *CurrentBR = CondBB->getTerminator();
1159 // Move exit condition into split condition block.
1160 EC->moveBefore(CurrentBR);
1161 EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
1163 // Move exiting block's branch into split condition block. Update its branch
1165 BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
1166 ExitingBR->moveBefore(CurrentBR);
1167 if (ExitingBR->getSuccessor(0) == ExitBB)
1168 ExitingBR->setSuccessor(1, ActiveBB);
1170 ExitingBR->setSuccessor(0, ActiveBB);
1172 // Remove split condition and current split condition branch.
1173 SC->eraseFromParent();
1174 CurrentBR->eraseFromParent();
1176 // Connect exiting block to split condition block.
1177 new BranchInst(CondBB, ExitingBB);
1180 updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd);
1182 // Fix dominator info.
1183 // ExitBB is now dominated by CondBB
1184 DT->changeImmediateDominator(ExitBB, CondBB);
1185 DF->changeImmediateDominator(ExitBB, CondBB, DT);
1187 // Basicblocks dominated by ActiveBB may have ExitingBB or
1188 // a basic block outside the loop in their DF list. If so,
1189 // replace it with CondBB.
1190 DomTreeNode *Node = DT->getNode(ActiveBB);
1191 for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
1193 BasicBlock *BB = DI->getBlock();
1194 DominanceFrontier::iterator BBDF = DF->find(BB);
1195 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1196 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1197 while (DomSetI != DomSetE) {
1198 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1200 BasicBlock *DFBB = *CurrentItr;
1201 if (DFBB == ExitingBB || !L->contains(DFBB)) {
1202 BBDF->second.erase(DFBB);
1203 BBDF->second.insert(CondBB);
1209 /// updatePHINodes - CFG has been changed.
1211 /// - ExitBB's single predecessor was Latch
1212 /// - Latch's second successor was Header
1214 /// - ExitBB's single predecessor was Header
1215 /// - Latch's one and only successor was Header
1217 /// Update ExitBB PHINodes' to reflect this change.
1218 void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
1220 PHINode *IV, Instruction *IVIncrement) {
1222 for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
1224 PHINode *PN = dyn_cast<PHINode>(BI);
1228 Value *V = PN->getIncomingValueForBlock(Latch);
1229 if (PHINode *PHV = dyn_cast<PHINode>(V)) {
1230 // PHV is in Latch. PHV has two uses, one use is in ExitBB PHINode
1232 // The second use is in Header and it is new incoming value for PN.
1236 for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
1239 U1 = cast<PHINode>(*UI);
1241 U2 = cast<PHINode>(*UI);
1243 assert ( 0 && "Unexpected third use of this PHINode");
1245 assert (U1 && U2 && "Unable to find two uses");
1247 if (U1->getParent() == Header)
1251 PN->addIncoming(NewV, Header);
1253 } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
1254 // If this instruction is IVIncrement then IV is new incoming value
1255 // from header otherwise this instruction must be incoming value from
1256 // header because loop is in LCSSA form.
1257 if (PHI == IVIncrement)
1258 PN->addIncoming(IV, Header);
1260 PN->addIncoming(V, Header);
1262 // Otherwise this is an incoming value from header because loop is in
1264 PN->addIncoming(V, Header);
1266 // Remove incoming value from Latch.
1267 PN->removeIncomingValue(Latch);