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 instruction compares IndVar against SplitValue.
68 Instruction *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;
93 // safeIcmpInst - CI is considered safe instruction if one of the operand
94 // is SCEVAddRecExpr based on induction variable and other operand is
95 // loop invariant. If CI is safe then populate SplitInfo object SD appropriately
97 bool safeICmpInst(ICmpInst *CI, SplitInfo &SD);
99 /// Find condition inside a loop that is suitable candidate for index split.
100 void findSplitCondition();
102 /// Find loop's exit condition.
103 void findLoopConditionals();
105 /// Return induction variable associated with value V.
106 void findIndVar(Value *V, Loop *L);
108 /// processOneIterationLoop - Current loop L contains compare instruction
109 /// that compares induction variable, IndVar, agains loop invariant. If
110 /// entire (i.e. meaningful) loop body is dominated by this compare
111 /// instruction then loop body is executed only for one iteration. In
112 /// such case eliminate loop structure surrounding this loop body. For
113 bool processOneIterationLoop(SplitInfo &SD);
115 void updateLoopBounds(ICmpInst *CI);
116 /// updateLoopIterationSpace - Current loop body is covered by an AND
117 /// instruction whose operands compares induction variables with loop
118 /// invariants. If possible, hoist this check outside the loop by
119 /// updating appropriate start and end values for induction variable.
120 bool updateLoopIterationSpace(SplitInfo &SD);
122 /// If loop header includes loop variant instruction operands then
123 /// this loop may not be eliminated.
124 bool safeHeader(SplitInfo &SD, BasicBlock *BB);
126 /// If Exiting block includes loop variant instructions then this
127 /// loop may not be eliminated.
128 bool safeExitingBlock(SplitInfo &SD, BasicBlock *BB);
130 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
131 /// This routine is used to remove split condition's dead branch, dominated by
132 /// DeadBB. LiveBB dominates split conidition's other branch.
133 void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB);
135 /// safeSplitCondition - Return true if it is possible to
136 /// split loop using given split condition.
137 bool safeSplitCondition(SplitInfo &SD);
139 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
140 /// based on split value.
141 void calculateLoopBounds(SplitInfo &SD);
143 /// updatePHINodes - CFG has been changed.
145 /// - ExitBB's single predecessor was Latch
146 /// - Latch's second successor was Header
148 /// - ExitBB's single predecessor was Header
149 /// - Latch's one and only successor was Header
151 /// Update ExitBB PHINodes' to reflect this change.
152 void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
154 PHINode *IV, Instruction *IVIncrement);
156 /// moveExitCondition - Move exit condition EC into split condition block CondBB.
157 void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
158 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
159 PHINode *IV, Instruction *IVAdd, Loop *LP);
161 /// splitLoop - Split current loop L in two loops using split information
162 /// SD. Update dominator information. Maintain LCSSA form.
163 bool splitLoop(SplitInfo &SD);
167 IndVarIncrement = NULL;
168 ExitCondition = NULL;
182 DominanceFrontier *DF;
183 SmallVector<SplitInfo, 4> SplitData;
185 // Induction variable whose range is being split by this transformation.
187 Instruction *IndVarIncrement;
189 // Loop exit condition.
190 ICmpInst *ExitCondition;
192 // Induction variable's initial value.
195 // Induction variable's final loop exit value operand number in exit condition..
196 unsigned ExitValueNum;
199 char LoopIndexSplit::ID = 0;
200 RegisterPass<LoopIndexSplit> X ("loop-index-split", "Index Split Loops");
203 LoopPass *llvm::createLoopIndexSplitPass() {
204 return new LoopIndexSplit();
207 // Index split Loop L. Return true if loop is split.
208 bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
209 bool Changed = false;
213 // FIXME - Nested loops make dominator info updates tricky.
214 if (!L->getSubLoops().empty())
217 SE = &getAnalysis<ScalarEvolution>();
218 DT = &getAnalysis<DominatorTree>();
219 LI = &getAnalysis<LoopInfo>();
220 DF = &getAnalysis<DominanceFrontier>();
224 findLoopConditionals();
229 findSplitCondition();
231 if (SplitData.empty())
234 // First see if it is possible to eliminate loop itself or not.
235 for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin(),
236 E = SplitData.end(); SI != E;) {
238 ICmpInst *CI = dyn_cast<ICmpInst>(SD.SplitCondition);
239 if (SD.SplitCondition->getOpcode() == Instruction::And) {
240 Changed = updateLoopIterationSpace(SD);
243 // If is loop is eliminated then nothing else to do here.
246 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
248 SplitData.erase(Delete_SI);
251 else if (CI && CI->getPredicate() == ICmpInst::ICMP_EQ) {
252 Changed = processOneIterationLoop(SD);
255 // If is loop is eliminated then nothing else to do here.
258 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
260 SplitData.erase(Delete_SI);
266 if (SplitData.empty())
269 // Split most profitiable condition.
270 // FIXME : Implement cost analysis.
271 unsigned MostProfitableSDIndex = 0;
272 Changed = splitLoop(SplitData[MostProfitableSDIndex]);
280 /// Return true if V is a induction variable or induction variable's
281 /// increment for loop L.
282 void LoopIndexSplit::findIndVar(Value *V, Loop *L) {
284 Instruction *I = dyn_cast<Instruction>(V);
288 // Check if I is a phi node from loop header or not.
289 if (PHINode *PN = dyn_cast<PHINode>(V)) {
290 if (PN->getParent() == L->getHeader()) {
296 // Check if I is a add instruction whose one operand is
297 // phi node from loop header and second operand is constant.
298 if (I->getOpcode() != Instruction::Add)
301 Value *Op0 = I->getOperand(0);
302 Value *Op1 = I->getOperand(1);
304 if (PHINode *PN = dyn_cast<PHINode>(Op0)) {
305 if (PN->getParent() == L->getHeader()
306 && isa<ConstantInt>(Op1)) {
313 if (PHINode *PN = dyn_cast<PHINode>(Op1)) {
314 if (PN->getParent() == L->getHeader()
315 && isa<ConstantInt>(Op0)) {
325 // Find loop's exit condition and associated induction variable.
326 void LoopIndexSplit::findLoopConditionals() {
328 BasicBlock *ExitingBlock = NULL;
330 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
333 if (!L->isLoopExit(BB))
343 // If exiting block is neither loop header nor loop latch then this loop is
345 if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch())
348 // If exit block's terminator is conditional branch inst then we have found
350 BranchInst *BR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
351 if (!BR || BR->isUnconditional())
354 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
359 if (CI->getPredicate() == ICmpInst::ICMP_SGT
360 || CI->getPredicate() == ICmpInst::ICMP_UGT
361 || CI->getPredicate() == ICmpInst::ICMP_SGE
362 || CI->getPredicate() == ICmpInst::ICMP_UGE
363 || CI->getPredicate() == ICmpInst::ICMP_EQ
364 || CI->getPredicate() == ICmpInst::ICMP_NE)
369 // Exit condition's one operand is loop invariant exit value and second
370 // operand is SCEVAddRecExpr based on induction variable.
371 Value *V0 = CI->getOperand(0);
372 Value *V1 = CI->getOperand(1);
374 SCEVHandle SH0 = SE->getSCEV(V0);
375 SCEVHandle SH1 = SE->getSCEV(V1);
377 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
381 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
387 ExitCondition = NULL;
389 BasicBlock *Preheader = L->getLoopPreheader();
390 StartValue = IndVar->getIncomingValueForBlock(Preheader);
394 /// Find condition inside a loop that is suitable candidate for index split.
395 void LoopIndexSplit::findSplitCondition() {
398 // Check all basic block's terminators.
399 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
404 // If this basic block does not terminate in a conditional branch
405 // then terminator is not a suitable split condition.
406 BranchInst *BR = dyn_cast<BranchInst>(BB->getTerminator());
410 if (BR->isUnconditional())
413 if (Instruction *AndI = dyn_cast<Instruction>(BR->getCondition())) {
414 if (AndI->getOpcode() == Instruction::And) {
415 ICmpInst *Op0 = dyn_cast<ICmpInst>(AndI->getOperand(0));
416 ICmpInst *Op1 = dyn_cast<ICmpInst>(AndI->getOperand(1));
421 if (!safeICmpInst(Op0, SD))
424 if (!safeICmpInst(Op1, SD))
427 SD.SplitCondition = AndI;
428 SplitData.push_back(SD);
432 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
433 if (!CI || CI == ExitCondition)
436 if (CI->getPredicate() == ICmpInst::ICMP_NE)
439 // If split condition predicate is GT or GE then first execute
440 // false branch of split condition.
441 if (CI->getPredicate() == ICmpInst::ICMP_UGT
442 || CI->getPredicate() == ICmpInst::ICMP_SGT
443 || CI->getPredicate() == ICmpInst::ICMP_UGE
444 || CI->getPredicate() == ICmpInst::ICMP_SGE)
445 SD.UseTrueBranchFirst = false;
447 // If one operand is loop invariant and second operand is SCEVAddRecExpr
448 // based on induction variable then CI is a candidate split condition.
449 if (safeICmpInst(CI, SD))
450 SplitData.push_back(SD);
454 // safeIcmpInst - CI is considered safe instruction if one of the operand
455 // is SCEVAddRecExpr based on induction variable and other operand is
456 // loop invariant. If CI is safe then populate SplitInfo object SD appropriately
458 bool LoopIndexSplit::safeICmpInst(ICmpInst *CI, SplitInfo &SD) {
460 Value *V0 = CI->getOperand(0);
461 Value *V1 = CI->getOperand(1);
463 SCEVHandle SH0 = SE->getSCEV(V0);
464 SCEVHandle SH1 = SE->getSCEV(V1);
466 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
468 SD.SplitCondition = CI;
469 if (PHINode *PN = dyn_cast<PHINode>(V1)) {
473 else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
474 if (IndVarIncrement && IndVarIncrement == Insn)
478 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
480 SD.SplitCondition = CI;
481 if (PHINode *PN = dyn_cast<PHINode>(V0)) {
485 else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
486 if (IndVarIncrement && IndVarIncrement == Insn)
494 /// processOneIterationLoop - Current loop L contains compare instruction
495 /// that compares induction variable, IndVar, against loop invariant. If
496 /// entire (i.e. meaningful) loop body is dominated by this compare
497 /// instruction then loop body is executed only once. In such case eliminate
498 /// loop structure surrounding this loop body. For example,
499 /// for (int i = start; i < end; ++i) {
500 /// if ( i == somevalue) {
504 /// can be transformed into
505 /// if (somevalue >= start && somevalue < end) {
509 bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
511 BasicBlock *Header = L->getHeader();
513 // First of all, check if SplitCondition dominates entire loop body
516 // If SplitCondition is not in loop header then this loop is not suitable
517 // for this transformation.
518 if (SD.SplitCondition->getParent() != Header)
521 // If loop header includes loop variant instruction operands then
522 // this loop may not be eliminated.
523 if (!safeHeader(SD, Header))
526 // If Exiting block includes loop variant instructions then this
527 // loop may not be eliminated.
528 if (!safeExitingBlock(SD, ExitCondition->getParent()))
531 // If split condition is not safe then do not process this loop.
533 // for(int i = 0; i < N; i++) {
542 if (!safeSplitCondition(SD))
547 // Replace index variable with split value in loop body. Loop body is executed
548 // only when index variable is equal to split value.
549 IndVar->replaceAllUsesWith(SD.SplitValue);
551 // Remove Latch to Header edge.
552 BasicBlock *Latch = L->getLoopLatch();
553 BasicBlock *LatchSucc = NULL;
554 BranchInst *BR = dyn_cast<BranchInst>(Latch->getTerminator());
557 Header->removePredecessor(Latch);
558 for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
563 BR->setUnconditionalDest(LatchSucc);
565 Instruction *Terminator = Header->getTerminator();
566 Value *ExitValue = ExitCondition->getOperand(ExitValueNum);
568 // Replace split condition in header.
570 // SplitCondition : icmp eq i32 IndVar, SplitValue
572 // c1 = icmp uge i32 SplitValue, StartValue
573 // c2 = icmp ult i32 SplitValue, ExitValue
575 bool SignedPredicate = ExitCondition->isSignedPredicate();
576 Instruction *C1 = new ICmpInst(SignedPredicate ?
577 ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
578 SD.SplitValue, StartValue, "lisplit",
580 Instruction *C2 = new ICmpInst(SignedPredicate ?
581 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
582 SD.SplitValue, ExitValue, "lisplit",
584 Instruction *NSplitCond = BinaryOperator::createAnd(C1, C2, "lisplit",
586 SD.SplitCondition->replaceAllUsesWith(NSplitCond);
587 SD.SplitCondition->eraseFromParent();
589 // Now, clear latch block. Remove instructions that are responsible
590 // to increment induction variable.
591 Instruction *LTerminator = Latch->getTerminator();
592 for (BasicBlock::iterator LB = Latch->begin(), LE = Latch->end();
596 if (isa<PHINode>(I) || I == LTerminator)
599 if (I == IndVarIncrement)
600 I->replaceAllUsesWith(ExitValue);
602 I->replaceAllUsesWith(UndefValue::get(I->getType()));
603 I->eraseFromParent();
606 LPM->deleteLoopFromQueue(L);
608 // Update Dominator Info.
609 // Only CFG change done is to remove Latch to Header edge. This
610 // does not change dominator tree because Latch did not dominate
613 DominanceFrontier::iterator HeaderDF = DF->find(Header);
614 if (HeaderDF != DF->end())
615 DF->removeFromFrontier(HeaderDF, Header);
617 DominanceFrontier::iterator LatchDF = DF->find(Latch);
618 if (LatchDF != DF->end())
619 DF->removeFromFrontier(LatchDF, Header);
624 // If loop header includes loop variant instruction operands then
625 // this loop can not be eliminated. This is used by processOneIterationLoop().
626 bool LoopIndexSplit::safeHeader(SplitInfo &SD, BasicBlock *Header) {
628 Instruction *Terminator = Header->getTerminator();
629 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
637 // SplitCondition itself is OK.
638 if (I == SD.SplitCondition)
641 // Induction variable is OK.
645 // Induction variable increment is OK.
646 if (I == IndVarIncrement)
649 // Terminator is also harmless.
653 // Otherwise we have a instruction that may not be safe.
660 // If Exiting block includes loop variant instructions then this
661 // loop may not be eliminated. This is used by processOneIterationLoop().
662 bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD,
663 BasicBlock *ExitingBlock) {
665 for (BasicBlock::iterator BI = ExitingBlock->begin(),
666 BE = ExitingBlock->end(); BI != BE; ++BI) {
673 // Induction variable increment is OK.
674 if (IndVarIncrement && IndVarIncrement == I)
677 // Check if I is induction variable increment instruction.
678 if (!IndVarIncrement && I->getOpcode() == Instruction::Add) {
680 Value *Op0 = I->getOperand(0);
681 Value *Op1 = I->getOperand(1);
683 ConstantInt *CI = NULL;
685 if ((PN = dyn_cast<PHINode>(Op0))) {
686 if ((CI = dyn_cast<ConstantInt>(Op1)))
689 if ((PN = dyn_cast<PHINode>(Op1))) {
690 if ((CI = dyn_cast<ConstantInt>(Op0)))
694 if (IndVarIncrement && PN == IndVar && CI->isOne())
698 // I is an Exit condition if next instruction is block terminator.
699 // Exit condition is OK if it compares loop invariant exit value,
700 // which is checked below.
701 else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
702 if (EC == ExitCondition)
706 if (I == ExitingBlock->getTerminator())
709 // Otherwise we have instruction that may not be safe.
713 // We could not find any reason to consider ExitingBlock unsafe.
717 void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) {
719 Value *V0 = CI->getOperand(0);
720 Value *V1 = CI->getOperand(1);
723 SCEVHandle SH0 = SE->getSCEV(V0);
725 if (SH0->isLoopInvariant(L))
730 switch (CI->getPredicate()) {
731 case ICmpInst::ICMP_ULE:
732 case ICmpInst::ICMP_SLE:
733 // for (i = LB; i < UB; ++i)
734 // if (i <= NV && ...)
737 // is transformed into
738 // NUB = min (NV+1, UB)
739 // for (i = LB; i < NUB ; ++i)
745 // for (i = LB; i <= UB; ++i)
746 // if (i <= NV && ...)
749 // is transformed into
750 // NUB = min (NV, UB)
751 // for (i = LB; i <= NUB ; ++i)
755 case ICmpInst::ICMP_ULT:
756 case ICmpInst::ICMP_SLT:
757 // for (i = LB; i < UB; ++i)
758 // if (i < NV && ...)
761 // is transformed into
762 // NUB = min (NV, UB)
763 // for (i = LB; i < NUB ; ++i)
769 // for (i = LB; i <= UB; ++i)
770 // if (i < NV && ...)
773 // is transformed into
774 // NUB = min (NV -1 , UB)
775 // for (i = LB; i <= NUB ; ++i)
779 case ICmpInst::ICMP_UGE:
780 case ICmpInst::ICMP_SGE:
781 // for (i = LB; i (< or <=) UB; ++i)
782 // if (i >= NV && ...)
785 // is transformed into
786 // NLB = max (NV, LB)
787 // for (i = NLB; i (< or <=) UB ; ++i)
791 case ICmpInst::ICMP_UGT:
792 case ICmpInst::ICMP_SGT:
793 // for (i = LB; i (< or <=) UB; ++i)
794 // if (i > NV && ...)
797 // is transformed into
798 // NLB = max (NV+1, LB)
799 // for (i = NLB; i (< or <=) UB ; ++i)
804 assert ( 0 && "Unexpected split condition predicate");
807 /// updateLoopIterationSpace - Current loop body is covered by an AND
808 /// instruction whose operands compares induction variables with loop
809 /// invariants. If possible, hoist this check outside the loop by
810 /// updating appropriate start and end values for induction variable.
811 bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) {
812 BasicBlock *Header = L->getHeader();
813 ICmpInst *Op0 = cast<ICmpInst>(SD.SplitCondition->getOperand(0));
814 ICmpInst *Op1 = cast<ICmpInst>(SD.SplitCondition->getOperand(1));
816 if (Op0->getPredicate() == ICmpInst::ICMP_EQ
817 || Op0->getPredicate() == ICmpInst::ICMP_NE
818 || Op0->getPredicate() == ICmpInst::ICMP_EQ
819 || Op0->getPredicate() == ICmpInst::ICMP_NE)
822 // Check if SplitCondition dominates entire loop body
825 // If SplitCondition is not in loop header then this loop is not suitable
826 // for this transformation.
827 if (SD.SplitCondition->getParent() != Header)
830 // If loop header includes loop variant instruction operands then
831 // this loop may not be eliminated.
832 Instruction *Terminator = Header->getTerminator();
833 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
841 // SplitCondition itself is OK.
842 if (I == SD.SplitCondition)
844 if (I == Op0 || I == Op1)
847 // Induction variable is OK.
851 // Induction variable increment is OK.
852 if (I == IndVarIncrement)
855 // Terminator is also harmless.
859 // Otherwise we have a instruction that may not be safe.
863 // If Exiting block includes loop variant instructions then this
864 // loop may not be eliminated.
865 if (!safeExitingBlock(SD, ExitCondition->getParent()))
868 updateLoopBounds(Op0);
869 updateLoopBounds(Op1);
875 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
876 /// This routine is used to remove split condition's dead branch, dominated by
877 /// DeadBB. LiveBB dominates split conidition's other branch.
878 void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
879 BasicBlock *LiveBB) {
881 // First update DeadBB's dominance frontier.
882 SmallVector<BasicBlock *, 8> FrontierBBs;
883 DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
884 if (DeadBBDF != DF->end()) {
885 SmallVector<BasicBlock *, 8> PredBlocks;
887 DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
888 for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
889 DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
890 BasicBlock *FrontierBB = *DeadBBSetI;
891 FrontierBBs.push_back(FrontierBB);
893 // Rremove any PHI incoming edge from blocks dominated by DeadBB.
895 for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
898 if (P == DeadBB || DT->dominates(DeadBB, P))
899 PredBlocks.push_back(P);
902 for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
904 if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
905 for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
906 PE = PredBlocks.end(); PI != PE; ++PI) {
908 PN->removeIncomingValue(P);
917 // Now remove DeadBB and all nodes dominated by DeadBB in df order.
918 SmallVector<BasicBlock *, 32> WorkList;
919 DomTreeNode *DN = DT->getNode(DeadBB);
920 for (df_iterator<DomTreeNode*> DI = df_begin(DN),
921 E = df_end(DN); DI != E; ++DI) {
922 BasicBlock *BB = DI->getBlock();
923 WorkList.push_back(BB);
924 BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
927 while (!WorkList.empty()) {
928 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
929 for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
931 Instruction *I = BBI;
932 I->replaceAllUsesWith(UndefValue::get(I->getType()));
933 I->eraseFromParent();
935 LPM->deleteSimpleAnalysisValue(BB, LP);
939 BB->eraseFromParent();
942 // Update Frontier BBs' dominator info.
943 while (!FrontierBBs.empty()) {
944 BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
945 BasicBlock *NewDominator = FBB->getSinglePredecessor();
947 pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
950 if (NewDominator != LiveBB) {
951 for(; PI != PE; ++PI) {
954 NewDominator = LiveBB;
957 NewDominator = DT->findNearestCommonDominator(NewDominator, P);
961 assert (NewDominator && "Unable to fix dominator info.");
962 DT->changeImmediateDominator(FBB, NewDominator);
963 DF->changeImmediateDominator(FBB, NewDominator, DT);
968 /// safeSplitCondition - Return true if it is possible to
969 /// split loop using given split condition.
970 bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
972 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
973 BasicBlock *Latch = L->getLoopLatch();
974 BranchInst *SplitTerminator =
975 cast<BranchInst>(SplitCondBlock->getTerminator());
976 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
977 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
979 // Finally this split condition is safe only if merge point for
980 // split condition branch is loop latch. This check along with previous
981 // check, to ensure that exit condition is in either loop latch or header,
982 // filters all loops with non-empty loop body between merge point
983 // and exit condition.
984 DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
985 assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
986 if (Succ0DF->second.count(Latch))
989 DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
990 assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
991 if (Succ1DF->second.count(Latch))
997 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
998 /// based on split value.
999 void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
1001 ICmpInst *SC = cast<ICmpInst>(SD.SplitCondition);
1002 ICmpInst::Predicate SP = SC->getPredicate();
1003 const Type *Ty = SD.SplitValue->getType();
1004 bool Sign = ExitCondition->isSignedPredicate();
1005 BasicBlock *Preheader = L->getLoopPreheader();
1006 Instruction *PHTerminator = Preheader->getTerminator();
1008 // Initially use split value as upper loop bound for first loop and lower loop
1009 // bound for second loop.
1010 Value *AEV = SD.SplitValue;
1011 Value *BSV = SD.SplitValue;
1013 switch (ExitCondition->getPredicate()) {
1014 case ICmpInst::ICMP_SGT:
1015 case ICmpInst::ICMP_UGT:
1016 case ICmpInst::ICMP_SGE:
1017 case ICmpInst::ICMP_UGE:
1019 assert (0 && "Unexpected exit condition predicate");
1021 case ICmpInst::ICMP_SLT:
1022 case ICmpInst::ICMP_ULT:
1025 case ICmpInst::ICMP_SLT:
1026 case ICmpInst::ICMP_ULT:
1028 // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
1030 // is transformed into
1032 // for (i = LB; i < min(UB, AEV); ++i)
1034 // for (i = max(LB, BSV); i < UB; ++i);
1037 case ICmpInst::ICMP_SLE:
1038 case ICmpInst::ICMP_ULE:
1041 // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
1043 // is transformed into
1047 // for (i = LB; i < min(UB, AEV); ++i)
1049 // for (i = max(LB, BSV); i < UB; ++i)
1051 BSV = BinaryOperator::createAdd(SD.SplitValue,
1052 ConstantInt::get(Ty, 1, Sign),
1053 "lsplit.add", PHTerminator);
1057 case ICmpInst::ICMP_SGE:
1058 case ICmpInst::ICMP_UGE:
1060 // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
1062 // is transformed into
1064 // for (i = LB; i < min(UB, AEV); ++i)
1066 // for (i = max(BSV, LB); i < UB; ++i)
1069 case ICmpInst::ICMP_SGT:
1070 case ICmpInst::ICMP_UGT:
1073 // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
1075 // is transformed into
1077 // BSV = AEV = SV + 1
1078 // for (i = LB; i < min(UB, AEV); ++i)
1080 // for (i = max(LB, BSV); i < UB; ++i)
1082 BSV = BinaryOperator::createAdd(SD.SplitValue,
1083 ConstantInt::get(Ty, 1, Sign),
1084 "lsplit.add", PHTerminator);
1089 assert (0 && "Unexpected split condition predicate");
1091 } // end switch (SP)
1094 case ICmpInst::ICMP_SLE:
1095 case ICmpInst::ICMP_ULE:
1098 case ICmpInst::ICMP_SLT:
1099 case ICmpInst::ICMP_ULT:
1101 // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
1103 // is transformed into
1106 // for (i = LB; i <= min(UB, AEV); ++i)
1108 // for (i = max(LB, BSV); i <= UB; ++i)
1110 AEV = BinaryOperator::createSub(SD.SplitValue,
1111 ConstantInt::get(Ty, 1, Sign),
1112 "lsplit.sub", PHTerminator);
1114 case ICmpInst::ICMP_SLE:
1115 case ICmpInst::ICMP_ULE:
1117 // for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; }
1119 // is transformed into
1122 // for (i = LB; i <= min(UB, AEV); ++i)
1124 // for (i = max(LB, BSV); i <= UB; ++i)
1126 BSV = BinaryOperator::createAdd(SD.SplitValue,
1127 ConstantInt::get(Ty, 1, Sign),
1128 "lsplit.add", PHTerminator);
1130 case ICmpInst::ICMP_SGT:
1131 case ICmpInst::ICMP_UGT:
1133 // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
1135 // is transformed into
1138 // for (i = LB; i <= min(AEV, UB); ++i)
1140 // for (i = max(LB, BSV); i <= UB; ++i)
1142 BSV = BinaryOperator::createAdd(SD.SplitValue,
1143 ConstantInt::get(Ty, 1, Sign),
1144 "lsplit.add", PHTerminator);
1146 case ICmpInst::ICMP_SGE:
1147 case ICmpInst::ICMP_UGE:
1150 // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
1152 // is transformed into
1155 // for (i = LB; i <= min(AEV, UB); ++i)
1157 // for (i = max(LB, BSV); i <= UB; ++i)
1159 AEV = BinaryOperator::createSub(SD.SplitValue,
1160 ConstantInt::get(Ty, 1, Sign),
1161 "lsplit.sub", PHTerminator);
1164 assert (0 && "Unexpected split condition predicate");
1166 } // end switch (SP)
1171 // Calculate ALoop induction variable's new exiting value and
1172 // BLoop induction variable's new starting value. Calculuate these
1173 // values in original loop's preheader.
1174 // A_ExitValue = min(SplitValue, OrignalLoopExitValue)
1175 // B_StartValue = max(SplitValue, OriginalLoopStartValue)
1176 Value *C1 = new ICmpInst(Sign ?
1177 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1179 ExitCondition->getOperand(ExitValueNum),
1180 "lsplit.ev", PHTerminator);
1181 SD.A_ExitValue = new SelectInst(C1, AEV,
1182 ExitCondition->getOperand(ExitValueNum),
1183 "lsplit.ev", PHTerminator);
1185 Value *C2 = new ICmpInst(Sign ?
1186 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1187 BSV, StartValue, "lsplit.sv",
1189 SD.B_StartValue = new SelectInst(C2, StartValue, BSV,
1190 "lsplit.sv", PHTerminator);
1193 /// splitLoop - Split current loop L in two loops using split information
1194 /// SD. Update dominator information. Maintain LCSSA form.
1195 bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
1197 if (!safeSplitCondition(SD))
1200 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1202 // Unable to handle triange loops at the moment.
1203 // In triangle loop, split condition is in header and one of the
1204 // the split destination is loop latch. If split condition is EQ
1205 // then such loops are already handle in processOneIterationLoop().
1206 BasicBlock *Latch = L->getLoopLatch();
1207 BranchInst *SplitTerminator =
1208 cast<BranchInst>(SplitCondBlock->getTerminator());
1209 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1210 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1211 if (L->getHeader() == SplitCondBlock
1212 && (Latch == Succ0 || Latch == Succ1))
1215 // If split condition branches heads do not have single predecessor,
1216 // SplitCondBlock, then is not possible to remove inactive branch.
1217 if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor())
1220 // After loop is cloned there are two loops.
1222 // First loop, referred as ALoop, executes first part of loop's iteration
1223 // space split. Second loop, referred as BLoop, executes remaining
1224 // part of loop's iteration space.
1226 // ALoop's exit edge enters BLoop's header through a forwarding block which
1227 // acts as a BLoop's preheader.
1228 BasicBlock *Preheader = L->getLoopPreheader();
1230 // Calculate ALoop induction variable's new exiting value and
1231 // BLoop induction variable's new starting value.
1232 calculateLoopBounds(SD);
1235 DenseMap<const Value *, Value *> ValueMap;
1236 Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
1238 BasicBlock *B_Header = BLoop->getHeader();
1240 //[*] ALoop's exiting edge BLoop's header.
1241 // ALoop's original exit block becomes BLoop's exit block.
1242 PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
1243 BasicBlock *A_ExitingBlock = ExitCondition->getParent();
1244 BranchInst *A_ExitInsn =
1245 dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
1246 assert (A_ExitInsn && "Unable to find suitable loop exit branch");
1247 BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
1248 if (L->contains(B_ExitBlock)) {
1249 B_ExitBlock = A_ExitInsn->getSuccessor(0);
1250 A_ExitInsn->setSuccessor(0, B_Header);
1252 A_ExitInsn->setSuccessor(1, B_Header);
1254 //[*] Update ALoop's exit value using new exit value.
1255 ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
1257 // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
1258 // original loop's preheader. Add incoming PHINode values from
1259 // ALoop's exiting block. Update BLoop header's domiantor info.
1261 // Collect inverse map of Header PHINodes.
1262 DenseMap<Value *, Value *> InverseMap;
1263 for (BasicBlock::iterator BI = L->getHeader()->begin(),
1264 BE = L->getHeader()->end(); BI != BE; ++BI) {
1265 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1266 PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
1267 InverseMap[PNClone] = PN;
1272 for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1274 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1275 // Remove incoming value from original preheader.
1276 PN->removeIncomingValue(Preheader);
1278 // Add incoming value from A_ExitingBlock.
1280 PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
1282 PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
1283 Value *V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
1284 PN->addIncoming(V2, A_ExitingBlock);
1289 DT->changeImmediateDominator(B_Header, A_ExitingBlock);
1290 DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
1292 // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
1293 // block. Remove incoming PHINode values from ALoop's exiting block.
1294 // Add new incoming values from BLoop's incoming exiting value.
1295 // Update BLoop exit block's dominator info..
1296 BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
1297 for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
1299 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1300 PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
1302 PN->removeIncomingValue(A_ExitingBlock);
1307 DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
1308 DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
1310 //[*] Split ALoop's exit edge. This creates a new block which
1311 // serves two purposes. First one is to hold PHINode defnitions
1312 // to ensure that ALoop's LCSSA form. Second use it to act
1313 // as a preheader for BLoop.
1314 BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
1316 //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
1317 // in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
1318 for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1320 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1321 Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
1322 PHINode *newPHI = new PHINode(PN->getType(), PN->getName());
1323 newPHI->addIncoming(V1, A_ExitingBlock);
1324 A_ExitBlock->getInstList().push_front(newPHI);
1325 PN->removeIncomingValue(A_ExitBlock);
1326 PN->addIncoming(newPHI, A_ExitBlock);
1331 //[*] Eliminate split condition's inactive branch from ALoop.
1332 BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
1333 BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
1334 BasicBlock *A_InactiveBranch = NULL;
1335 BasicBlock *A_ActiveBranch = NULL;
1336 if (SD.UseTrueBranchFirst) {
1337 A_ActiveBranch = A_BR->getSuccessor(0);
1338 A_InactiveBranch = A_BR->getSuccessor(1);
1340 A_ActiveBranch = A_BR->getSuccessor(1);
1341 A_InactiveBranch = A_BR->getSuccessor(0);
1343 A_BR->setUnconditionalDest(A_ActiveBranch);
1344 removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
1346 //[*] Eliminate split condition's inactive branch in from BLoop.
1347 BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
1348 BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
1349 BasicBlock *B_InactiveBranch = NULL;
1350 BasicBlock *B_ActiveBranch = NULL;
1351 if (SD.UseTrueBranchFirst) {
1352 B_ActiveBranch = B_BR->getSuccessor(1);
1353 B_InactiveBranch = B_BR->getSuccessor(0);
1355 B_ActiveBranch = B_BR->getSuccessor(0);
1356 B_InactiveBranch = B_BR->getSuccessor(1);
1358 B_BR->setUnconditionalDest(B_ActiveBranch);
1359 removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
1361 BasicBlock *A_Header = L->getHeader();
1362 if (A_ExitingBlock == A_Header)
1365 //[*] Move exit condition into split condition block to avoid
1366 // executing dead loop iteration.
1367 ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
1368 Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
1369 ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
1371 moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
1372 cast<ICmpInst>(SD.SplitCondition), IndVar, IndVarIncrement,
1375 moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
1376 B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
1381 // moveExitCondition - Move exit condition EC into split condition block CondBB.
1382 void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
1383 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
1384 PHINode *IV, Instruction *IVAdd, Loop *LP) {
1386 BasicBlock *ExitingBB = EC->getParent();
1387 Instruction *CurrentBR = CondBB->getTerminator();
1389 // Move exit condition into split condition block.
1390 EC->moveBefore(CurrentBR);
1391 EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
1393 // Move exiting block's branch into split condition block. Update its branch
1395 BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
1396 ExitingBR->moveBefore(CurrentBR);
1397 if (ExitingBR->getSuccessor(0) == ExitBB)
1398 ExitingBR->setSuccessor(1, ActiveBB);
1400 ExitingBR->setSuccessor(0, ActiveBB);
1402 // Remove split condition and current split condition branch.
1403 SC->eraseFromParent();
1404 CurrentBR->eraseFromParent();
1406 // Connect exiting block to split condition block.
1407 new BranchInst(CondBB, ExitingBB);
1410 updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd);
1412 // Fix dominator info.
1413 // ExitBB is now dominated by CondBB
1414 DT->changeImmediateDominator(ExitBB, CondBB);
1415 DF->changeImmediateDominator(ExitBB, CondBB, DT);
1417 // Basicblocks dominated by ActiveBB may have ExitingBB or
1418 // a basic block outside the loop in their DF list. If so,
1419 // replace it with CondBB.
1420 DomTreeNode *Node = DT->getNode(ActiveBB);
1421 for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
1423 BasicBlock *BB = DI->getBlock();
1424 DominanceFrontier::iterator BBDF = DF->find(BB);
1425 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1426 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1427 while (DomSetI != DomSetE) {
1428 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1430 BasicBlock *DFBB = *CurrentItr;
1431 if (DFBB == ExitingBB || !L->contains(DFBB)) {
1432 BBDF->second.erase(DFBB);
1433 BBDF->second.insert(CondBB);
1439 /// updatePHINodes - CFG has been changed.
1441 /// - ExitBB's single predecessor was Latch
1442 /// - Latch's second successor was Header
1444 /// - ExitBB's single predecessor was Header
1445 /// - Latch's one and only successor was Header
1447 /// Update ExitBB PHINodes' to reflect this change.
1448 void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
1450 PHINode *IV, Instruction *IVIncrement) {
1452 for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
1454 PHINode *PN = dyn_cast<PHINode>(BI);
1458 Value *V = PN->getIncomingValueForBlock(Latch);
1459 if (PHINode *PHV = dyn_cast<PHINode>(V)) {
1460 // PHV is in Latch. PHV has two uses, one use is in ExitBB PHINode
1462 // The second use is in Header and it is new incoming value for PN.
1466 for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
1469 U1 = cast<PHINode>(*UI);
1471 U2 = cast<PHINode>(*UI);
1473 assert ( 0 && "Unexpected third use of this PHINode");
1475 assert (U1 && U2 && "Unable to find two uses");
1477 if (U1->getParent() == Header)
1481 PN->addIncoming(NewV, Header);
1483 } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
1484 // If this instruction is IVIncrement then IV is new incoming value
1485 // from header otherwise this instruction must be incoming value from
1486 // header because loop is in LCSSA form.
1487 if (PHI == IVIncrement)
1488 PN->addIncoming(IV, Header);
1490 PN->addIncoming(V, Header);
1492 // Otherwise this is an incoming value from header because loop is in
1494 PN->addIncoming(V, Header);
1496 // Remove incoming value from Latch.
1497 PN->removeIncomingValue(Latch);