1 //===- LoopIndexSplit.cpp - Loop Index Splitting Pass ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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(&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 /// isOneIterationLoop - Return true if split condition is EQ and
116 /// the IV is not used outside the loop.
117 bool isOneIterationLoop(ICmpInst *CI);
119 void updateLoopBounds(ICmpInst *CI);
120 /// updateLoopIterationSpace - Current loop body is covered by an AND
121 /// instruction whose operands compares induction variables with loop
122 /// invariants. If possible, hoist this check outside the loop by
123 /// updating appropriate start and end values for induction variable.
124 bool updateLoopIterationSpace(SplitInfo &SD);
126 /// If loop header includes loop variant instruction operands then
127 /// this loop may not be eliminated.
128 bool safeHeader(SplitInfo &SD, BasicBlock *BB);
130 /// If Exiting block includes loop variant instructions then this
131 /// loop may not be eliminated.
132 bool safeExitingBlock(SplitInfo &SD, BasicBlock *BB);
134 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
135 /// This routine is used to remove split condition's dead branch, dominated by
136 /// DeadBB. LiveBB dominates split conidition's other branch.
137 void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB);
139 /// safeSplitCondition - Return true if it is possible to
140 /// split loop using given split condition.
141 bool safeSplitCondition(SplitInfo &SD);
143 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
144 /// based on split value.
145 void calculateLoopBounds(SplitInfo &SD);
147 /// updatePHINodes - CFG has been changed.
149 /// - ExitBB's single predecessor was Latch
150 /// - Latch's second successor was Header
152 /// - ExitBB's single predecessor was Header
153 /// - Latch's one and only successor was Header
155 /// Update ExitBB PHINodes' to reflect this change.
156 void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
158 PHINode *IV, Instruction *IVIncrement, Loop *LP);
160 /// moveExitCondition - Move exit condition EC into split condition block CondBB.
161 void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
162 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
163 PHINode *IV, Instruction *IVAdd, Loop *LP);
165 /// splitLoop - Split current loop L in two loops using split information
166 /// SD. Update dominator information. Maintain LCSSA form.
167 bool splitLoop(SplitInfo &SD);
171 IndVarIncrement = NULL;
172 ExitCondition = NULL;
186 DominanceFrontier *DF;
187 SmallVector<SplitInfo, 4> SplitData;
189 // Induction variable whose range is being split by this transformation.
191 Instruction *IndVarIncrement;
193 // Loop exit condition.
194 ICmpInst *ExitCondition;
196 // Induction variable's initial value.
199 // Induction variable's final loop exit value operand number in exit condition..
200 unsigned ExitValueNum;
204 char LoopIndexSplit::ID = 0;
205 static RegisterPass<LoopIndexSplit>
206 X("loop-index-split", "Index Split Loops");
208 LoopPass *llvm::createLoopIndexSplitPass() {
209 return new LoopIndexSplit();
212 // Index split Loop L. Return true if loop is split.
213 bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
214 bool Changed = false;
218 // FIXME - Nested loops make dominator info updates tricky.
219 if (!L->getSubLoops().empty())
222 SE = &getAnalysis<ScalarEvolution>();
223 DT = &getAnalysis<DominatorTree>();
224 LI = &getAnalysis<LoopInfo>();
225 DF = &getAnalysis<DominanceFrontier>();
229 findLoopConditionals();
234 findSplitCondition();
236 if (SplitData.empty())
239 // First see if it is possible to eliminate loop itself or not.
240 for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin();
241 SI != SplitData.end();) {
243 ICmpInst *CI = dyn_cast<ICmpInst>(SD.SplitCondition);
244 if (SD.SplitCondition->getOpcode() == Instruction::And) {
245 Changed = updateLoopIterationSpace(SD);
248 // If is loop is eliminated then nothing else to do here.
251 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
252 SI = SplitData.erase(Delete_SI);
255 else if (isOneIterationLoop(CI)) {
256 Changed = processOneIterationLoop(SD);
259 // If is loop is eliminated then nothing else to do here.
262 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
263 SI = SplitData.erase(Delete_SI);
269 if (SplitData.empty())
272 // Split most profitiable condition.
273 // FIXME : Implement cost analysis.
274 unsigned MostProfitableSDIndex = 0;
275 Changed = splitLoop(SplitData[MostProfitableSDIndex]);
283 /// isOneIterationLoop - Return true if split condition is EQ and
284 /// the IV is not used outside the loop.
285 bool LoopIndexSplit::isOneIterationLoop(ICmpInst *CI) {
288 if (CI->getPredicate() != ICmpInst::ICMP_EQ)
291 Value *Incr = IndVar->getIncomingValueForBlock(L->getLoopLatch());
292 for (Value::use_iterator UI = Incr->use_begin(), E = Incr->use_end();
294 if (!L->contains(cast<Instruction>(*UI)->getParent()))
299 /// Return true if V is a induction variable or induction variable's
300 /// increment for loop L.
301 void LoopIndexSplit::findIndVar(Value *V, Loop *L) {
303 Instruction *I = dyn_cast<Instruction>(V);
307 // Check if I is a phi node from loop header or not.
308 if (PHINode *PN = dyn_cast<PHINode>(V)) {
309 if (PN->getParent() == L->getHeader()) {
315 // Check if I is a add instruction whose one operand is
316 // phi node from loop header and second operand is constant.
317 if (I->getOpcode() != Instruction::Add)
320 Value *Op0 = I->getOperand(0);
321 Value *Op1 = I->getOperand(1);
323 if (PHINode *PN = dyn_cast<PHINode>(Op0))
324 if (PN->getParent() == L->getHeader())
325 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1))
332 if (PHINode *PN = dyn_cast<PHINode>(Op1))
333 if (PN->getParent() == L->getHeader())
334 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0))
344 // Find loop's exit condition and associated induction variable.
345 void LoopIndexSplit::findLoopConditionals() {
347 BasicBlock *ExitingBlock = NULL;
349 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
352 if (!L->isLoopExit(BB))
362 // If exiting block is neither loop header nor loop latch then this loop is
364 if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch())
367 // If exit block's terminator is conditional branch inst then we have found
369 BranchInst *BR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
370 if (!BR || BR->isUnconditional())
373 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
378 if (CI->getPredicate() == ICmpInst::ICMP_EQ
379 || CI->getPredicate() == ICmpInst::ICMP_NE)
384 // Exit condition's one operand is loop invariant exit value and second
385 // operand is SCEVAddRecExpr based on induction variable.
386 Value *V0 = CI->getOperand(0);
387 Value *V1 = CI->getOperand(1);
389 SCEVHandle SH0 = SE->getSCEV(V0);
390 SCEVHandle SH1 = SE->getSCEV(V1);
392 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
396 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
402 ExitCondition = NULL;
404 BasicBlock *Preheader = L->getLoopPreheader();
405 StartValue = IndVar->getIncomingValueForBlock(Preheader);
408 // If start value is more then exit value where induction variable
409 // increments by 1 then we are potentially dealing with an infinite loop.
410 // Do not index split this loop.
412 ConstantInt *SV = dyn_cast<ConstantInt>(StartValue);
414 dyn_cast<ConstantInt>(ExitCondition->getOperand(ExitValueNum));
415 if (SV && EV && SV->getSExtValue() > EV->getSExtValue())
416 ExitCondition = NULL;
417 else if (EV && EV->isZero())
418 ExitCondition = NULL;
422 /// Find condition inside a loop that is suitable candidate for index split.
423 void LoopIndexSplit::findSplitCondition() {
426 // Check all basic block's terminators.
427 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
432 // If this basic block does not terminate in a conditional branch
433 // then terminator is not a suitable split condition.
434 BranchInst *BR = dyn_cast<BranchInst>(BB->getTerminator());
438 if (BR->isUnconditional())
441 if (Instruction *AndI = dyn_cast<Instruction>(BR->getCondition())) {
442 if (AndI->getOpcode() == Instruction::And) {
443 ICmpInst *Op0 = dyn_cast<ICmpInst>(AndI->getOperand(0));
444 ICmpInst *Op1 = dyn_cast<ICmpInst>(AndI->getOperand(1));
449 if (!safeICmpInst(Op0, SD))
452 if (!safeICmpInst(Op1, SD))
455 SD.SplitCondition = AndI;
456 SplitData.push_back(SD);
460 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
461 if (!CI || CI == ExitCondition)
464 if (CI->getPredicate() == ICmpInst::ICMP_NE)
467 // If split condition predicate is GT or GE then first execute
468 // false branch of split condition.
469 if (CI->getPredicate() == ICmpInst::ICMP_UGT
470 || CI->getPredicate() == ICmpInst::ICMP_SGT
471 || CI->getPredicate() == ICmpInst::ICMP_UGE
472 || CI->getPredicate() == ICmpInst::ICMP_SGE)
473 SD.UseTrueBranchFirst = false;
475 // If one operand is loop invariant and second operand is SCEVAddRecExpr
476 // based on induction variable then CI is a candidate split condition.
477 if (safeICmpInst(CI, SD))
478 SplitData.push_back(SD);
482 // safeIcmpInst - CI is considered safe instruction if one of the operand
483 // is SCEVAddRecExpr based on induction variable and other operand is
484 // loop invariant. If CI is safe then populate SplitInfo object SD appropriately
486 bool LoopIndexSplit::safeICmpInst(ICmpInst *CI, SplitInfo &SD) {
488 Value *V0 = CI->getOperand(0);
489 Value *V1 = CI->getOperand(1);
491 SCEVHandle SH0 = SE->getSCEV(V0);
492 SCEVHandle SH1 = SE->getSCEV(V1);
494 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
496 SD.SplitCondition = CI;
497 if (PHINode *PN = dyn_cast<PHINode>(V1)) {
501 else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
502 if (IndVarIncrement && IndVarIncrement == Insn)
506 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
508 SD.SplitCondition = CI;
509 if (PHINode *PN = dyn_cast<PHINode>(V0)) {
513 else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
514 if (IndVarIncrement && IndVarIncrement == Insn)
522 /// processOneIterationLoop - Current loop L contains compare instruction
523 /// that compares induction variable, IndVar, against loop invariant. If
524 /// entire (i.e. meaningful) loop body is dominated by this compare
525 /// instruction then loop body is executed only once. In such case eliminate
526 /// loop structure surrounding this loop body. For example,
527 /// for (int i = start; i < end; ++i) {
528 /// if ( i == somevalue) {
532 /// can be transformed into
533 /// if (somevalue >= start && somevalue < end) {
537 bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
539 BasicBlock *Header = L->getHeader();
541 // First of all, check if SplitCondition dominates entire loop body
544 // If SplitCondition is not in loop header then this loop is not suitable
545 // for this transformation.
546 if (SD.SplitCondition->getParent() != Header)
549 // If loop header includes loop variant instruction operands then
550 // this loop may not be eliminated.
551 if (!safeHeader(SD, Header))
554 // If Exiting block includes loop variant instructions then this
555 // loop may not be eliminated.
556 if (!safeExitingBlock(SD, ExitCondition->getParent()))
559 // Filter loops where split condition's false branch is not empty.
560 if (ExitCondition->getParent() != Header->getTerminator()->getSuccessor(1))
563 // If split condition is not safe then do not process this loop.
565 // for(int i = 0; i < N; i++) {
574 if (!safeSplitCondition(SD))
577 BasicBlock *Latch = L->getLoopLatch();
578 BranchInst *BR = dyn_cast<BranchInst>(Latch->getTerminator());
584 // Replace index variable with split value in loop body. Loop body is executed
585 // only when index variable is equal to split value.
586 IndVar->replaceAllUsesWith(SD.SplitValue);
588 // Remove Latch to Header edge.
589 BasicBlock *LatchSucc = NULL;
590 Header->removePredecessor(Latch);
591 for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
596 BR->setUnconditionalDest(LatchSucc);
598 Instruction *Terminator = Header->getTerminator();
599 Value *ExitValue = ExitCondition->getOperand(ExitValueNum);
601 // Replace split condition in header.
603 // SplitCondition : icmp eq i32 IndVar, SplitValue
605 // c1 = icmp uge i32 SplitValue, StartValue
606 // c2 = icmp ult i32 SplitValue, ExitValue
608 bool SignedPredicate = ExitCondition->isSignedPredicate();
609 Instruction *C1 = new ICmpInst(SignedPredicate ?
610 ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
611 SD.SplitValue, StartValue, "lisplit",
613 Instruction *C2 = new ICmpInst(SignedPredicate ?
614 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
615 SD.SplitValue, ExitValue, "lisplit",
617 Instruction *NSplitCond = BinaryOperator::CreateAnd(C1, C2, "lisplit",
619 SD.SplitCondition->replaceAllUsesWith(NSplitCond);
620 SD.SplitCondition->eraseFromParent();
622 // Now, clear latch block. Remove instructions that are responsible
623 // to increment induction variable.
624 Instruction *LTerminator = Latch->getTerminator();
625 for (BasicBlock::iterator LB = Latch->begin(), LE = Latch->end();
629 if (isa<PHINode>(I) || I == LTerminator)
632 if (I == IndVarIncrement) {
633 // Replace induction variable increment if it is not used outside
635 bool UsedOutsideLoop = false;
636 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
638 if (Instruction *Use = dyn_cast<Instruction>(UI))
639 if (!L->contains(Use->getParent())) {
640 UsedOutsideLoop = true;
644 if (!UsedOutsideLoop) {
645 I->replaceAllUsesWith(ExitValue);
646 I->eraseFromParent();
650 I->replaceAllUsesWith(UndefValue::get(I->getType()));
651 I->eraseFromParent();
655 LPM->deleteLoopFromQueue(L);
657 // Update Dominator Info.
658 // Only CFG change done is to remove Latch to Header edge. This
659 // does not change dominator tree because Latch did not dominate
662 DominanceFrontier::iterator HeaderDF = DF->find(Header);
663 if (HeaderDF != DF->end())
664 DF->removeFromFrontier(HeaderDF, Header);
666 DominanceFrontier::iterator LatchDF = DF->find(Latch);
667 if (LatchDF != DF->end())
668 DF->removeFromFrontier(LatchDF, Header);
673 // If loop header includes loop variant instruction operands then
674 // this loop can not be eliminated. This is used by processOneIterationLoop().
675 bool LoopIndexSplit::safeHeader(SplitInfo &SD, BasicBlock *Header) {
677 Instruction *Terminator = Header->getTerminator();
678 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
686 // SplitCondition itself is OK.
687 if (I == SD.SplitCondition)
690 // Induction variable is OK.
694 // Induction variable increment is OK.
695 if (I == IndVarIncrement)
698 // Terminator is also harmless.
702 // Otherwise we have a instruction that may not be safe.
709 // If Exiting block includes loop variant instructions then this
710 // loop may not be eliminated. This is used by processOneIterationLoop().
711 bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD,
712 BasicBlock *ExitingBlock) {
714 for (BasicBlock::iterator BI = ExitingBlock->begin(),
715 BE = ExitingBlock->end(); BI != BE; ++BI) {
722 // Induction variable increment is OK.
723 if (IndVarIncrement && IndVarIncrement == I)
726 // Check if I is induction variable increment instruction.
727 if (I->getOpcode() == Instruction::Add) {
729 Value *Op0 = I->getOperand(0);
730 Value *Op1 = I->getOperand(1);
732 ConstantInt *CI = NULL;
734 if ((PN = dyn_cast<PHINode>(Op0))) {
735 if ((CI = dyn_cast<ConstantInt>(Op1)))
737 if (!IndVarIncrement && PN == IndVar)
739 // else this is another loop induction variable
743 if ((PN = dyn_cast<PHINode>(Op1))) {
744 if ((CI = dyn_cast<ConstantInt>(Op0)))
746 if (!IndVarIncrement && PN == IndVar)
748 // else this is another loop induction variable
754 // I is an Exit condition if next instruction is block terminator.
755 // Exit condition is OK if it compares loop invariant exit value,
756 // which is checked below.
757 else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
758 if (EC == ExitCondition)
762 if (I == ExitingBlock->getTerminator())
765 // Otherwise we have instruction that may not be safe.
769 // We could not find any reason to consider ExitingBlock unsafe.
773 void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) {
775 Value *V0 = CI->getOperand(0);
776 Value *V1 = CI->getOperand(1);
779 SCEVHandle SH0 = SE->getSCEV(V0);
781 if (SH0->isLoopInvariant(L))
786 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
787 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
788 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
789 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
790 ExitCondition->swapOperands();
799 Value *UB = ExitCondition->getOperand(ExitValueNum);
800 const Type *Ty = NV->getType();
801 bool Sign = ExitCondition->isSignedPredicate();
802 BasicBlock *Preheader = L->getLoopPreheader();
803 Instruction *PHTerminator = Preheader->getTerminator();
805 assert (NV && "Unexpected value");
807 switch (CI->getPredicate()) {
808 case ICmpInst::ICMP_ULE:
809 case ICmpInst::ICMP_SLE:
810 // for (i = LB; i < UB; ++i)
811 // if (i <= NV && ...)
814 // is transformed into
815 // NUB = min (NV+1, UB)
816 // for (i = LB; i < NUB ; ++i)
819 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
820 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
821 Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign),
822 "lsplit.add", PHTerminator);
823 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
824 A, UB,"lsplit,c", PHTerminator);
825 NUB = SelectInst::Create(C, A, UB, "lsplit.nub", PHTerminator);
828 // for (i = LB; i <= UB; ++i)
829 // if (i <= NV && ...)
832 // is transformed into
833 // NUB = min (NV, UB)
834 // for (i = LB; i <= NUB ; ++i)
837 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
838 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
839 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
840 NV, UB, "lsplit.c", PHTerminator);
841 NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator);
844 case ICmpInst::ICMP_ULT:
845 case ICmpInst::ICMP_SLT:
846 // for (i = LB; i < UB; ++i)
847 // if (i < NV && ...)
850 // is transformed into
851 // NUB = min (NV, UB)
852 // for (i = LB; i < NUB ; ++i)
855 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
856 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
857 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
858 NV, UB, "lsplit.c", PHTerminator);
859 NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator);
862 // for (i = LB; i <= UB; ++i)
863 // if (i < NV && ...)
866 // is transformed into
867 // NUB = min (NV -1 , UB)
868 // for (i = LB; i <= NUB ; ++i)
871 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
872 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
873 Value *S = BinaryOperator::CreateSub(NV, ConstantInt::get(Ty, 1, Sign),
874 "lsplit.add", PHTerminator);
875 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
876 S, UB, "lsplit.c", PHTerminator);
877 NUB = SelectInst::Create(C, S, UB, "lsplit.nub", PHTerminator);
880 case ICmpInst::ICMP_UGE:
881 case ICmpInst::ICMP_SGE:
882 // for (i = LB; i (< or <=) UB; ++i)
883 // if (i >= NV && ...)
886 // is transformed into
887 // NLB = max (NV, LB)
888 // for (i = NLB; i (< or <=) UB ; ++i)
892 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
893 NV, StartValue, "lsplit.c", PHTerminator);
894 NLB = SelectInst::Create(C, StartValue, NV, "lsplit.nlb", PHTerminator);
897 case ICmpInst::ICMP_UGT:
898 case ICmpInst::ICMP_SGT:
899 // for (i = LB; i (< or <=) UB; ++i)
900 // if (i > NV && ...)
903 // is transformed into
904 // NLB = max (NV+1, LB)
905 // for (i = NLB; i (< or <=) UB ; ++i)
909 Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign),
910 "lsplit.add", PHTerminator);
911 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
912 A, StartValue, "lsplit.c", PHTerminator);
913 NLB = SelectInst::Create(C, StartValue, A, "lsplit.nlb", PHTerminator);
917 assert ( 0 && "Unexpected split condition predicate");
921 unsigned i = IndVar->getBasicBlockIndex(Preheader);
922 IndVar->setIncomingValue(i, NLB);
926 ExitCondition->setOperand(ExitValueNum, NUB);
929 /// updateLoopIterationSpace - Current loop body is covered by an AND
930 /// instruction whose operands compares induction variables with loop
931 /// invariants. If possible, hoist this check outside the loop by
932 /// updating appropriate start and end values for induction variable.
933 bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) {
934 BasicBlock *Header = L->getHeader();
935 BasicBlock *ExitingBlock = ExitCondition->getParent();
936 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
938 ICmpInst *Op0 = cast<ICmpInst>(SD.SplitCondition->getOperand(0));
939 ICmpInst *Op1 = cast<ICmpInst>(SD.SplitCondition->getOperand(1));
941 if (Op0->getPredicate() == ICmpInst::ICMP_EQ
942 || Op0->getPredicate() == ICmpInst::ICMP_NE
943 || Op0->getPredicate() == ICmpInst::ICMP_EQ
944 || Op0->getPredicate() == ICmpInst::ICMP_NE)
947 // Check if SplitCondition dominates entire loop body
950 // If SplitCondition is not in loop header then this loop is not suitable
951 // for this transformation.
952 if (SD.SplitCondition->getParent() != Header)
955 // If loop header includes loop variant instruction operands then
956 // this loop may not be eliminated.
957 Instruction *Terminator = Header->getTerminator();
958 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
966 // SplitCondition itself is OK.
967 if (I == SD.SplitCondition)
969 if (I == Op0 || I == Op1)
972 // Induction variable is OK.
976 // Induction variable increment is OK.
977 if (I == IndVarIncrement)
980 // Terminator is also harmless.
984 // Otherwise we have a instruction that may not be safe.
988 // If Exiting block includes loop variant instructions then this
989 // loop may not be eliminated.
990 if (!safeExitingBlock(SD, ExitCondition->getParent()))
993 // Verify that loop exiting block has only two predecessor, where one predecessor
994 // is split condition block. The other predecessor will become exiting block's
995 // dominator after CFG is updated. TODO : Handle CFG's where exiting block has
996 // more then two predecessors. This requires extra work in updating dominator
998 BasicBlock *ExitingBBPred = NULL;
999 for (pred_iterator PI = pred_begin(ExitingBlock), PE = pred_end(ExitingBlock);
1001 BasicBlock *BB = *PI;
1002 if (SplitCondBlock == BB)
1010 // Update loop bounds to absorb Op0 check.
1011 updateLoopBounds(Op0);
1012 // Update loop bounds to absorb Op1 check.
1013 updateLoopBounds(Op1);
1017 // Unconditionally connect split block to its remaining successor.
1018 BranchInst *SplitTerminator =
1019 cast<BranchInst>(SplitCondBlock->getTerminator());
1020 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1021 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1022 if (Succ0 == ExitCondition->getParent())
1023 SplitTerminator->setUnconditionalDest(Succ1);
1025 SplitTerminator->setUnconditionalDest(Succ0);
1027 // Remove split condition.
1028 SD.SplitCondition->eraseFromParent();
1029 if (Op0->use_empty())
1030 Op0->eraseFromParent();
1031 if (Op1->use_empty())
1032 Op1->eraseFromParent();
1034 BranchInst *ExitInsn =
1035 dyn_cast<BranchInst>(ExitingBlock->getTerminator());
1036 assert (ExitInsn && "Unable to find suitable loop exit branch");
1037 BasicBlock *ExitBlock = ExitInsn->getSuccessor(1);
1038 if (L->contains(ExitBlock))
1039 ExitBlock = ExitInsn->getSuccessor(0);
1041 // Update domiantor info. Now, ExitingBlock has only one predecessor,
1042 // ExitingBBPred, and it is ExitingBlock's immediate domiantor.
1043 DT->changeImmediateDominator(ExitingBlock, ExitingBBPred);
1045 // If ExitingBlock is a member of loop BB's DF list then replace it with
1046 // loop header and exit block.
1047 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
1049 BasicBlock *BB = *I;
1050 if (BB == Header || BB == ExitingBlock)
1052 DominanceFrontier::iterator BBDF = DF->find(BB);
1053 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1054 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1055 while (DomSetI != DomSetE) {
1056 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1058 BasicBlock *DFBB = *CurrentItr;
1059 if (DFBB == ExitingBlock) {
1060 BBDF->second.erase(DFBB);
1061 BBDF->second.insert(Header);
1062 if (Header != ExitingBlock)
1063 BBDF->second.insert(ExitBlock);
1072 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
1073 /// This routine is used to remove split condition's dead branch, dominated by
1074 /// DeadBB. LiveBB dominates split conidition's other branch.
1075 void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
1076 BasicBlock *LiveBB) {
1078 // First update DeadBB's dominance frontier.
1079 SmallVector<BasicBlock *, 8> FrontierBBs;
1080 DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
1081 if (DeadBBDF != DF->end()) {
1082 SmallVector<BasicBlock *, 8> PredBlocks;
1084 DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
1085 for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
1086 DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
1087 BasicBlock *FrontierBB = *DeadBBSetI;
1088 FrontierBBs.push_back(FrontierBB);
1090 // Rremove any PHI incoming edge from blocks dominated by DeadBB.
1092 for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
1094 BasicBlock *P = *PI;
1095 if (P == DeadBB || DT->dominates(DeadBB, P))
1096 PredBlocks.push_back(P);
1099 for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
1100 FBI != FBE; ++FBI) {
1101 if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
1102 for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
1103 PE = PredBlocks.end(); PI != PE; ++PI) {
1104 BasicBlock *P = *PI;
1105 PN->removeIncomingValue(P);
1114 // Now remove DeadBB and all nodes dominated by DeadBB in df order.
1115 SmallVector<BasicBlock *, 32> WorkList;
1116 DomTreeNode *DN = DT->getNode(DeadBB);
1117 for (df_iterator<DomTreeNode*> DI = df_begin(DN),
1118 E = df_end(DN); DI != E; ++DI) {
1119 BasicBlock *BB = DI->getBlock();
1120 WorkList.push_back(BB);
1121 BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
1124 while (!WorkList.empty()) {
1125 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
1126 for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
1128 Instruction *I = BBI;
1130 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1131 I->eraseFromParent();
1133 LPM->deleteSimpleAnalysisValue(BB, LP);
1135 DF->removeBlock(BB);
1136 LI->removeBlock(BB);
1137 BB->eraseFromParent();
1140 // Update Frontier BBs' dominator info.
1141 while (!FrontierBBs.empty()) {
1142 BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
1143 BasicBlock *NewDominator = FBB->getSinglePredecessor();
1144 if (!NewDominator) {
1145 pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
1148 if (NewDominator != LiveBB) {
1149 for(; PI != PE; ++PI) {
1150 BasicBlock *P = *PI;
1152 NewDominator = LiveBB;
1155 NewDominator = DT->findNearestCommonDominator(NewDominator, P);
1159 assert (NewDominator && "Unable to fix dominator info.");
1160 DT->changeImmediateDominator(FBB, NewDominator);
1161 DF->changeImmediateDominator(FBB, NewDominator, DT);
1166 /// safeSplitCondition - Return true if it is possible to
1167 /// split loop using given split condition.
1168 bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
1170 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1171 BasicBlock *Latch = L->getLoopLatch();
1172 BranchInst *SplitTerminator =
1173 cast<BranchInst>(SplitCondBlock->getTerminator());
1174 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1175 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1177 // If split block does not dominate the latch then this is not a diamond.
1178 // Such loop may not benefit from index split.
1179 if (!DT->dominates(SplitCondBlock, Latch))
1182 // Finally this split condition is safe only if merge point for
1183 // split condition branch is loop latch. This check along with previous
1184 // check, to ensure that exit condition is in either loop latch or header,
1185 // filters all loops with non-empty loop body between merge point
1186 // and exit condition.
1187 DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
1188 assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
1189 if (Succ0DF->second.count(Latch))
1192 DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
1193 assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
1194 if (Succ1DF->second.count(Latch))
1200 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
1201 /// based on split value.
1202 void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
1204 ICmpInst *SC = cast<ICmpInst>(SD.SplitCondition);
1205 ICmpInst::Predicate SP = SC->getPredicate();
1206 const Type *Ty = SD.SplitValue->getType();
1207 bool Sign = ExitCondition->isSignedPredicate();
1208 BasicBlock *Preheader = L->getLoopPreheader();
1209 Instruction *PHTerminator = Preheader->getTerminator();
1211 // Initially use split value as upper loop bound for first loop and lower loop
1212 // bound for second loop.
1213 Value *AEV = SD.SplitValue;
1214 Value *BSV = SD.SplitValue;
1216 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
1217 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
1218 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
1219 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
1220 ExitCondition->swapOperands();
1227 switch (ExitCondition->getPredicate()) {
1228 case ICmpInst::ICMP_SGT:
1229 case ICmpInst::ICMP_UGT:
1230 case ICmpInst::ICMP_SGE:
1231 case ICmpInst::ICMP_UGE:
1233 assert (0 && "Unexpected exit condition predicate");
1235 case ICmpInst::ICMP_SLT:
1236 case ICmpInst::ICMP_ULT:
1239 case ICmpInst::ICMP_SLT:
1240 case ICmpInst::ICMP_ULT:
1242 // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
1244 // is transformed into
1246 // for (i = LB; i < min(UB, AEV); ++i)
1248 // for (i = max(LB, BSV); i < UB; ++i);
1251 case ICmpInst::ICMP_SLE:
1252 case ICmpInst::ICMP_ULE:
1255 // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
1257 // is transformed into
1261 // for (i = LB; i < min(UB, AEV); ++i)
1263 // for (i = max(LB, BSV); i < UB; ++i)
1265 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1266 ConstantInt::get(Ty, 1, Sign),
1267 "lsplit.add", PHTerminator);
1271 case ICmpInst::ICMP_SGE:
1272 case ICmpInst::ICMP_UGE:
1274 // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
1276 // is transformed into
1278 // for (i = LB; i < min(UB, AEV); ++i)
1280 // for (i = max(BSV, LB); i < UB; ++i)
1283 case ICmpInst::ICMP_SGT:
1284 case ICmpInst::ICMP_UGT:
1287 // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
1289 // is transformed into
1291 // BSV = AEV = SV + 1
1292 // for (i = LB; i < min(UB, AEV); ++i)
1294 // for (i = max(LB, BSV); i < UB; ++i)
1296 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1297 ConstantInt::get(Ty, 1, Sign),
1298 "lsplit.add", PHTerminator);
1303 assert (0 && "Unexpected split condition predicate");
1305 } // end switch (SP)
1308 case ICmpInst::ICMP_SLE:
1309 case ICmpInst::ICMP_ULE:
1312 case ICmpInst::ICMP_SLT:
1313 case ICmpInst::ICMP_ULT:
1315 // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
1317 // is transformed into
1320 // for (i = LB; i <= min(UB, AEV); ++i)
1322 // for (i = max(LB, BSV); i <= UB; ++i)
1324 AEV = BinaryOperator::CreateSub(SD.SplitValue,
1325 ConstantInt::get(Ty, 1, Sign),
1326 "lsplit.sub", PHTerminator);
1328 case ICmpInst::ICMP_SLE:
1329 case ICmpInst::ICMP_ULE:
1331 // for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; }
1333 // is transformed into
1336 // for (i = LB; i <= min(UB, AEV); ++i)
1338 // for (i = max(LB, BSV); i <= UB; ++i)
1340 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1341 ConstantInt::get(Ty, 1, Sign),
1342 "lsplit.add", PHTerminator);
1344 case ICmpInst::ICMP_SGT:
1345 case ICmpInst::ICMP_UGT:
1347 // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
1349 // is transformed into
1352 // for (i = LB; i <= min(AEV, UB); ++i)
1354 // for (i = max(LB, BSV); i <= UB; ++i)
1356 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1357 ConstantInt::get(Ty, 1, Sign),
1358 "lsplit.add", PHTerminator);
1360 case ICmpInst::ICMP_SGE:
1361 case ICmpInst::ICMP_UGE:
1364 // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
1366 // is transformed into
1369 // for (i = LB; i <= min(AEV, UB); ++i)
1371 // for (i = max(LB, BSV); i <= UB; ++i)
1373 AEV = BinaryOperator::CreateSub(SD.SplitValue,
1374 ConstantInt::get(Ty, 1, Sign),
1375 "lsplit.sub", PHTerminator);
1378 assert (0 && "Unexpected split condition predicate");
1380 } // end switch (SP)
1385 // Calculate ALoop induction variable's new exiting value and
1386 // BLoop induction variable's new starting value. Calculuate these
1387 // values in original loop's preheader.
1388 // A_ExitValue = min(SplitValue, OrignalLoopExitValue)
1389 // B_StartValue = max(SplitValue, OriginalLoopStartValue)
1390 Instruction *InsertPt = L->getHeader()->getFirstNonPHI();
1392 // If ExitValue operand is also defined in Loop header then
1393 // insert new ExitValue after this operand definition.
1394 if (Instruction *EVN =
1395 dyn_cast<Instruction>(ExitCondition->getOperand(ExitValueNum))) {
1396 if (!isa<PHINode>(EVN))
1397 if (InsertPt->getParent() == EVN->getParent()) {
1398 BasicBlock::iterator LHBI = L->getHeader()->begin();
1399 BasicBlock::iterator LHBE = L->getHeader()->end();
1400 for(;LHBI != LHBE; ++LHBI) {
1401 Instruction *I = LHBI;
1408 Value *C1 = new ICmpInst(Sign ?
1409 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1411 ExitCondition->getOperand(ExitValueNum),
1412 "lsplit.ev", InsertPt);
1414 SD.A_ExitValue = SelectInst::Create(C1, AEV,
1415 ExitCondition->getOperand(ExitValueNum),
1416 "lsplit.ev", InsertPt);
1418 Value *C2 = new ICmpInst(Sign ?
1419 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1420 BSV, StartValue, "lsplit.sv",
1422 SD.B_StartValue = SelectInst::Create(C2, StartValue, BSV,
1423 "lsplit.sv", PHTerminator);
1426 /// splitLoop - Split current loop L in two loops using split information
1427 /// SD. Update dominator information. Maintain LCSSA form.
1428 bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
1430 if (!safeSplitCondition(SD))
1433 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1435 // Unable to handle triangle loops at the moment.
1436 // In triangle loop, split condition is in header and one of the
1437 // the split destination is loop latch. If split condition is EQ
1438 // then such loops are already handle in processOneIterationLoop().
1439 BasicBlock *Latch = L->getLoopLatch();
1440 BranchInst *SplitTerminator =
1441 cast<BranchInst>(SplitCondBlock->getTerminator());
1442 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1443 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1444 if (L->getHeader() == SplitCondBlock
1445 && (Latch == Succ0 || Latch == Succ1))
1448 // If split condition branches heads do not have single predecessor,
1449 // SplitCondBlock, then is not possible to remove inactive branch.
1450 if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor())
1453 // If Exiting block includes loop variant instructions then this
1454 // loop may not be split safely.
1455 if (!safeExitingBlock(SD, ExitCondition->getParent()))
1458 // After loop is cloned there are two loops.
1460 // First loop, referred as ALoop, executes first part of loop's iteration
1461 // space split. Second loop, referred as BLoop, executes remaining
1462 // part of loop's iteration space.
1464 // ALoop's exit edge enters BLoop's header through a forwarding block which
1465 // acts as a BLoop's preheader.
1466 BasicBlock *Preheader = L->getLoopPreheader();
1468 // Calculate ALoop induction variable's new exiting value and
1469 // BLoop induction variable's new starting value.
1470 calculateLoopBounds(SD);
1473 DenseMap<const Value *, Value *> ValueMap;
1474 Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
1476 BasicBlock *B_Header = BLoop->getHeader();
1478 //[*] ALoop's exiting edge BLoop's header.
1479 // ALoop's original exit block becomes BLoop's exit block.
1480 PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
1481 BasicBlock *A_ExitingBlock = ExitCondition->getParent();
1482 BranchInst *A_ExitInsn =
1483 dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
1484 assert (A_ExitInsn && "Unable to find suitable loop exit branch");
1485 BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
1486 if (L->contains(B_ExitBlock)) {
1487 B_ExitBlock = A_ExitInsn->getSuccessor(0);
1488 A_ExitInsn->setSuccessor(0, B_Header);
1490 A_ExitInsn->setSuccessor(1, B_Header);
1492 //[*] Update ALoop's exit value using new exit value.
1493 ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
1495 // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
1496 // original loop's preheader. Add incoming PHINode values from
1497 // ALoop's exiting block. Update BLoop header's domiantor info.
1499 // Collect inverse map of Header PHINodes.
1500 DenseMap<Value *, Value *> InverseMap;
1501 for (BasicBlock::iterator BI = L->getHeader()->begin(),
1502 BE = L->getHeader()->end(); BI != BE; ++BI) {
1503 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1504 PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
1505 InverseMap[PNClone] = PN;
1510 for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1512 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1513 // Remove incoming value from original preheader.
1514 PN->removeIncomingValue(Preheader);
1516 // Add incoming value from A_ExitingBlock.
1518 PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
1520 PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
1522 // If loop header is also loop exiting block then
1523 // OrigPN is incoming value for B loop header.
1524 if (A_ExitingBlock == L->getHeader())
1527 V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
1528 PN->addIncoming(V2, A_ExitingBlock);
1533 DT->changeImmediateDominator(B_Header, A_ExitingBlock);
1534 DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
1536 // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
1537 // block. Remove incoming PHINode values from ALoop's exiting block.
1538 // Add new incoming values from BLoop's incoming exiting value.
1539 // Update BLoop exit block's dominator info..
1540 BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
1541 for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
1543 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1544 PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
1546 PN->removeIncomingValue(A_ExitingBlock);
1551 DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
1552 DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
1554 //[*] Split ALoop's exit edge. This creates a new block which
1555 // serves two purposes. First one is to hold PHINode defnitions
1556 // to ensure that ALoop's LCSSA form. Second use it to act
1557 // as a preheader for BLoop.
1558 BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
1560 //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
1561 // in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
1562 for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1564 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1565 Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
1566 PHINode *newPHI = PHINode::Create(PN->getType(), PN->getName());
1567 newPHI->addIncoming(V1, A_ExitingBlock);
1568 A_ExitBlock->getInstList().push_front(newPHI);
1569 PN->removeIncomingValue(A_ExitBlock);
1570 PN->addIncoming(newPHI, A_ExitBlock);
1575 //[*] Eliminate split condition's inactive branch from ALoop.
1576 BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
1577 BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
1578 BasicBlock *A_InactiveBranch = NULL;
1579 BasicBlock *A_ActiveBranch = NULL;
1580 if (SD.UseTrueBranchFirst) {
1581 A_ActiveBranch = A_BR->getSuccessor(0);
1582 A_InactiveBranch = A_BR->getSuccessor(1);
1584 A_ActiveBranch = A_BR->getSuccessor(1);
1585 A_InactiveBranch = A_BR->getSuccessor(0);
1587 A_BR->setUnconditionalDest(A_ActiveBranch);
1588 removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
1590 //[*] Eliminate split condition's inactive branch in from BLoop.
1591 BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
1592 BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
1593 BasicBlock *B_InactiveBranch = NULL;
1594 BasicBlock *B_ActiveBranch = NULL;
1595 if (SD.UseTrueBranchFirst) {
1596 B_ActiveBranch = B_BR->getSuccessor(1);
1597 B_InactiveBranch = B_BR->getSuccessor(0);
1599 B_ActiveBranch = B_BR->getSuccessor(0);
1600 B_InactiveBranch = B_BR->getSuccessor(1);
1602 B_BR->setUnconditionalDest(B_ActiveBranch);
1603 removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
1605 BasicBlock *A_Header = L->getHeader();
1606 if (A_ExitingBlock == A_Header)
1609 //[*] Move exit condition into split condition block to avoid
1610 // executing dead loop iteration.
1611 ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
1612 Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
1613 ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
1615 moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
1616 cast<ICmpInst>(SD.SplitCondition), IndVar, IndVarIncrement,
1619 moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
1620 B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
1625 // moveExitCondition - Move exit condition EC into split condition block CondBB.
1626 void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
1627 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
1628 PHINode *IV, Instruction *IVAdd, Loop *LP) {
1630 BasicBlock *ExitingBB = EC->getParent();
1631 Instruction *CurrentBR = CondBB->getTerminator();
1633 // Move exit condition into split condition block.
1634 EC->moveBefore(CurrentBR);
1635 EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
1637 // Move exiting block's branch into split condition block. Update its branch
1639 BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
1640 ExitingBR->moveBefore(CurrentBR);
1641 BasicBlock *OrigDestBB = NULL;
1642 if (ExitingBR->getSuccessor(0) == ExitBB) {
1643 OrigDestBB = ExitingBR->getSuccessor(1);
1644 ExitingBR->setSuccessor(1, ActiveBB);
1647 OrigDestBB = ExitingBR->getSuccessor(0);
1648 ExitingBR->setSuccessor(0, ActiveBB);
1651 // Remove split condition and current split condition branch.
1652 SC->eraseFromParent();
1653 CurrentBR->eraseFromParent();
1655 // Connect exiting block to original destination.
1656 BranchInst::Create(OrigDestBB, ExitingBB);
1659 updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd, LP);
1661 // Fix dominator info.
1662 // ExitBB is now dominated by CondBB
1663 DT->changeImmediateDominator(ExitBB, CondBB);
1664 DF->changeImmediateDominator(ExitBB, CondBB, DT);
1666 // Basicblocks dominated by ActiveBB may have ExitingBB or
1667 // a basic block outside the loop in their DF list. If so,
1668 // replace it with CondBB.
1669 DomTreeNode *Node = DT->getNode(ActiveBB);
1670 for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
1672 BasicBlock *BB = DI->getBlock();
1673 DominanceFrontier::iterator BBDF = DF->find(BB);
1674 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1675 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1676 while (DomSetI != DomSetE) {
1677 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1679 BasicBlock *DFBB = *CurrentItr;
1680 if (DFBB == ExitingBB || !L->contains(DFBB)) {
1681 BBDF->second.erase(DFBB);
1682 BBDF->second.insert(CondBB);
1688 /// updatePHINodes - CFG has been changed.
1690 /// - ExitBB's single predecessor was Latch
1691 /// - Latch's second successor was Header
1693 /// - ExitBB's single predecessor is Header
1694 /// - Latch's one and only successor is Header
1696 /// Update ExitBB PHINodes' to reflect this change.
1697 void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
1699 PHINode *IV, Instruction *IVIncrement,
1702 for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
1704 PHINode *PN = dyn_cast<PHINode>(BI);
1709 Value *V = PN->getIncomingValueForBlock(Latch);
1710 if (PHINode *PHV = dyn_cast<PHINode>(V)) {
1711 // PHV is in Latch. PHV has one use is in ExitBB PHINode. And one use
1712 // in Header which is new incoming value for PN.
1714 for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
1716 if (PHINode *U = dyn_cast<PHINode>(*UI))
1717 if (LP->contains(U->getParent())) {
1722 // Add incoming value from header only if PN has any use inside the loop.
1724 PN->addIncoming(NewV, Header);
1726 } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
1727 // If this instruction is IVIncrement then IV is new incoming value
1728 // from header otherwise this instruction must be incoming value from
1729 // header because loop is in LCSSA form.
1730 if (PHI == IVIncrement)
1731 PN->addIncoming(IV, Header);
1733 PN->addIncoming(V, Header);
1735 // Otherwise this is an incoming value from header because loop is in
1737 PN->addIncoming(V, Header);
1739 // Remove incoming value from Latch.
1740 PN->removeIncomingValue(Latch);