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((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, Loop *LP);
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;
200 char LoopIndexSplit::ID = 0;
201 static RegisterPass<LoopIndexSplit>
202 X("loop-index-split", "Index Split Loops");
204 LoopPass *llvm::createLoopIndexSplitPass() {
205 return new LoopIndexSplit();
208 // Index split Loop L. Return true if loop is split.
209 bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
210 bool Changed = false;
214 // FIXME - Nested loops make dominator info updates tricky.
215 if (!L->getSubLoops().empty())
218 SE = &getAnalysis<ScalarEvolution>();
219 DT = &getAnalysis<DominatorTree>();
220 LI = &getAnalysis<LoopInfo>();
221 DF = &getAnalysis<DominanceFrontier>();
225 findLoopConditionals();
230 findSplitCondition();
232 if (SplitData.empty())
235 // First see if it is possible to eliminate loop itself or not.
236 for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin();
237 SI != SplitData.end();) {
239 ICmpInst *CI = dyn_cast<ICmpInst>(SD.SplitCondition);
240 if (SD.SplitCondition->getOpcode() == Instruction::And) {
241 Changed = updateLoopIterationSpace(SD);
244 // If is loop is eliminated then nothing else to do here.
247 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
248 SI = 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;
259 SI = SplitData.erase(Delete_SI);
265 if (SplitData.empty())
268 // Split most profitiable condition.
269 // FIXME : Implement cost analysis.
270 unsigned MostProfitableSDIndex = 0;
271 Changed = splitLoop(SplitData[MostProfitableSDIndex]);
279 /// Return true if V is a induction variable or induction variable's
280 /// increment for loop L.
281 void LoopIndexSplit::findIndVar(Value *V, Loop *L) {
283 Instruction *I = dyn_cast<Instruction>(V);
287 // Check if I is a phi node from loop header or not.
288 if (PHINode *PN = dyn_cast<PHINode>(V)) {
289 if (PN->getParent() == L->getHeader()) {
295 // Check if I is a add instruction whose one operand is
296 // phi node from loop header and second operand is constant.
297 if (I->getOpcode() != Instruction::Add)
300 Value *Op0 = I->getOperand(0);
301 Value *Op1 = I->getOperand(1);
303 if (PHINode *PN = dyn_cast<PHINode>(Op0))
304 if (PN->getParent() == L->getHeader())
305 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1))
312 if (PHINode *PN = dyn_cast<PHINode>(Op1))
313 if (PN->getParent() == L->getHeader())
314 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0))
324 // Find loop's exit condition and associated induction variable.
325 void LoopIndexSplit::findLoopConditionals() {
327 BasicBlock *ExitingBlock = NULL;
329 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
332 if (!L->isLoopExit(BB))
342 // If exiting block is neither loop header nor loop latch then this loop is
344 if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch())
347 // If exit block's terminator is conditional branch inst then we have found
349 BranchInst *BR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
350 if (!BR || BR->isUnconditional())
353 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
358 if (CI->getPredicate() == ICmpInst::ICMP_EQ
359 || CI->getPredicate() == ICmpInst::ICMP_NE)
364 // Exit condition's one operand is loop invariant exit value and second
365 // operand is SCEVAddRecExpr based on induction variable.
366 Value *V0 = CI->getOperand(0);
367 Value *V1 = CI->getOperand(1);
369 SCEVHandle SH0 = SE->getSCEV(V0);
370 SCEVHandle SH1 = SE->getSCEV(V1);
372 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
376 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
382 ExitCondition = NULL;
384 BasicBlock *Preheader = L->getLoopPreheader();
385 StartValue = IndVar->getIncomingValueForBlock(Preheader);
389 /// Find condition inside a loop that is suitable candidate for index split.
390 void LoopIndexSplit::findSplitCondition() {
393 // Check all basic block's terminators.
394 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
399 // If this basic block does not terminate in a conditional branch
400 // then terminator is not a suitable split condition.
401 BranchInst *BR = dyn_cast<BranchInst>(BB->getTerminator());
405 if (BR->isUnconditional())
408 if (Instruction *AndI = dyn_cast<Instruction>(BR->getCondition())) {
409 if (AndI->getOpcode() == Instruction::And) {
410 ICmpInst *Op0 = dyn_cast<ICmpInst>(AndI->getOperand(0));
411 ICmpInst *Op1 = dyn_cast<ICmpInst>(AndI->getOperand(1));
416 if (!safeICmpInst(Op0, SD))
419 if (!safeICmpInst(Op1, SD))
422 SD.SplitCondition = AndI;
423 SplitData.push_back(SD);
427 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
428 if (!CI || CI == ExitCondition)
431 if (CI->getPredicate() == ICmpInst::ICMP_NE)
434 // If split condition predicate is GT or GE then first execute
435 // false branch of split condition.
436 if (CI->getPredicate() == ICmpInst::ICMP_UGT
437 || CI->getPredicate() == ICmpInst::ICMP_SGT
438 || CI->getPredicate() == ICmpInst::ICMP_UGE
439 || CI->getPredicate() == ICmpInst::ICMP_SGE)
440 SD.UseTrueBranchFirst = false;
442 // If one operand is loop invariant and second operand is SCEVAddRecExpr
443 // based on induction variable then CI is a candidate split condition.
444 if (safeICmpInst(CI, SD))
445 SplitData.push_back(SD);
449 // safeIcmpInst - CI is considered safe instruction if one of the operand
450 // is SCEVAddRecExpr based on induction variable and other operand is
451 // loop invariant. If CI is safe then populate SplitInfo object SD appropriately
453 bool LoopIndexSplit::safeICmpInst(ICmpInst *CI, SplitInfo &SD) {
455 Value *V0 = CI->getOperand(0);
456 Value *V1 = CI->getOperand(1);
458 SCEVHandle SH0 = SE->getSCEV(V0);
459 SCEVHandle SH1 = SE->getSCEV(V1);
461 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
463 SD.SplitCondition = CI;
464 if (PHINode *PN = dyn_cast<PHINode>(V1)) {
468 else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
469 if (IndVarIncrement && IndVarIncrement == Insn)
473 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
475 SD.SplitCondition = CI;
476 if (PHINode *PN = dyn_cast<PHINode>(V0)) {
480 else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
481 if (IndVarIncrement && IndVarIncrement == Insn)
489 /// processOneIterationLoop - Current loop L contains compare instruction
490 /// that compares induction variable, IndVar, against loop invariant. If
491 /// entire (i.e. meaningful) loop body is dominated by this compare
492 /// instruction then loop body is executed only once. In such case eliminate
493 /// loop structure surrounding this loop body. For example,
494 /// for (int i = start; i < end; ++i) {
495 /// if ( i == somevalue) {
499 /// can be transformed into
500 /// if (somevalue >= start && somevalue < end) {
504 bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
506 BasicBlock *Header = L->getHeader();
508 // First of all, check if SplitCondition dominates entire loop body
511 // If SplitCondition is not in loop header then this loop is not suitable
512 // for this transformation.
513 if (SD.SplitCondition->getParent() != Header)
516 // If loop header includes loop variant instruction operands then
517 // this loop may not be eliminated.
518 if (!safeHeader(SD, Header))
521 // If Exiting block includes loop variant instructions then this
522 // loop may not be eliminated.
523 if (!safeExitingBlock(SD, ExitCondition->getParent()))
526 // Filter loops where split condition's false branch is not empty.
527 if (ExitCondition->getParent() != Header->getTerminator()->getSuccessor(1))
530 // If split condition is not safe then do not process this loop.
532 // for(int i = 0; i < N; i++) {
541 if (!safeSplitCondition(SD))
544 BasicBlock *Latch = L->getLoopLatch();
545 BranchInst *BR = dyn_cast<BranchInst>(Latch->getTerminator());
551 // Replace index variable with split value in loop body. Loop body is executed
552 // only when index variable is equal to split value.
553 IndVar->replaceAllUsesWith(SD.SplitValue);
555 // Remove Latch to Header edge.
556 BasicBlock *LatchSucc = NULL;
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 (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)))
688 if (!IndVarIncrement && PN == IndVar)
690 // else this is another loop induction variable
694 if ((PN = dyn_cast<PHINode>(Op1))) {
695 if ((CI = dyn_cast<ConstantInt>(Op0)))
697 if (!IndVarIncrement && PN == IndVar)
699 // else this is another loop induction variable
705 // I is an Exit condition if next instruction is block terminator.
706 // Exit condition is OK if it compares loop invariant exit value,
707 // which is checked below.
708 else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
709 if (EC == ExitCondition)
713 if (I == ExitingBlock->getTerminator())
716 // Otherwise we have instruction that may not be safe.
720 // We could not find any reason to consider ExitingBlock unsafe.
724 void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) {
726 Value *V0 = CI->getOperand(0);
727 Value *V1 = CI->getOperand(1);
730 SCEVHandle SH0 = SE->getSCEV(V0);
732 if (SH0->isLoopInvariant(L))
737 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
738 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
739 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
740 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
741 ExitCondition->swapOperands();
750 Value *UB = ExitCondition->getOperand(ExitValueNum);
751 const Type *Ty = NV->getType();
752 bool Sign = ExitCondition->isSignedPredicate();
753 BasicBlock *Preheader = L->getLoopPreheader();
754 Instruction *PHTerminator = Preheader->getTerminator();
756 assert (NV && "Unexpected value");
758 switch (CI->getPredicate()) {
759 case ICmpInst::ICMP_ULE:
760 case ICmpInst::ICMP_SLE:
761 // for (i = LB; i < UB; ++i)
762 // if (i <= NV && ...)
765 // is transformed into
766 // NUB = min (NV+1, UB)
767 // for (i = LB; i < NUB ; ++i)
770 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
771 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
772 Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign),
773 "lsplit.add", PHTerminator);
774 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
775 A, UB,"lsplit,c", PHTerminator);
776 NUB = SelectInst::Create(C, A, UB, "lsplit.nub", PHTerminator);
779 // for (i = LB; i <= UB; ++i)
780 // if (i <= NV && ...)
783 // is transformed into
784 // NUB = min (NV, UB)
785 // for (i = LB; i <= NUB ; ++i)
788 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
789 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
790 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
791 NV, UB, "lsplit.c", PHTerminator);
792 NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator);
795 case ICmpInst::ICMP_ULT:
796 case ICmpInst::ICMP_SLT:
797 // for (i = LB; i < UB; ++i)
798 // if (i < NV && ...)
801 // is transformed into
802 // NUB = min (NV, UB)
803 // for (i = LB; i < NUB ; ++i)
806 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
807 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
808 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
809 NV, UB, "lsplit.c", PHTerminator);
810 NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator);
813 // for (i = LB; i <= UB; ++i)
814 // if (i < NV && ...)
817 // is transformed into
818 // NUB = min (NV -1 , UB)
819 // for (i = LB; i <= NUB ; ++i)
822 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
823 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
824 Value *S = BinaryOperator::CreateSub(NV, ConstantInt::get(Ty, 1, Sign),
825 "lsplit.add", PHTerminator);
826 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
827 S, UB, "lsplit.c", PHTerminator);
828 NUB = SelectInst::Create(C, S, UB, "lsplit.nub", PHTerminator);
831 case ICmpInst::ICMP_UGE:
832 case ICmpInst::ICMP_SGE:
833 // for (i = LB; i (< or <=) UB; ++i)
834 // if (i >= NV && ...)
837 // is transformed into
838 // NLB = max (NV, LB)
839 // for (i = NLB; i (< or <=) UB ; ++i)
843 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
844 NV, StartValue, "lsplit.c", PHTerminator);
845 NLB = SelectInst::Create(C, StartValue, NV, "lsplit.nlb", PHTerminator);
848 case ICmpInst::ICMP_UGT:
849 case ICmpInst::ICMP_SGT:
850 // for (i = LB; i (< or <=) UB; ++i)
851 // if (i > NV && ...)
854 // is transformed into
855 // NLB = max (NV+1, LB)
856 // for (i = NLB; i (< or <=) UB ; ++i)
860 Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign),
861 "lsplit.add", PHTerminator);
862 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
863 A, StartValue, "lsplit.c", PHTerminator);
864 NLB = SelectInst::Create(C, StartValue, A, "lsplit.nlb", PHTerminator);
868 assert ( 0 && "Unexpected split condition predicate");
872 unsigned i = IndVar->getBasicBlockIndex(Preheader);
873 IndVar->setIncomingValue(i, NLB);
877 ExitCondition->setOperand(ExitValueNum, NUB);
880 /// updateLoopIterationSpace - Current loop body is covered by an AND
881 /// instruction whose operands compares induction variables with loop
882 /// invariants. If possible, hoist this check outside the loop by
883 /// updating appropriate start and end values for induction variable.
884 bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) {
885 BasicBlock *Header = L->getHeader();
886 BasicBlock *ExitingBlock = ExitCondition->getParent();
887 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
889 ICmpInst *Op0 = cast<ICmpInst>(SD.SplitCondition->getOperand(0));
890 ICmpInst *Op1 = cast<ICmpInst>(SD.SplitCondition->getOperand(1));
892 if (Op0->getPredicate() == ICmpInst::ICMP_EQ
893 || Op0->getPredicate() == ICmpInst::ICMP_NE
894 || Op0->getPredicate() == ICmpInst::ICMP_EQ
895 || Op0->getPredicate() == ICmpInst::ICMP_NE)
898 // Check if SplitCondition dominates entire loop body
901 // If SplitCondition is not in loop header then this loop is not suitable
902 // for this transformation.
903 if (SD.SplitCondition->getParent() != Header)
906 // If loop header includes loop variant instruction operands then
907 // this loop may not be eliminated.
908 Instruction *Terminator = Header->getTerminator();
909 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
917 // SplitCondition itself is OK.
918 if (I == SD.SplitCondition)
920 if (I == Op0 || I == Op1)
923 // Induction variable is OK.
927 // Induction variable increment is OK.
928 if (I == IndVarIncrement)
931 // Terminator is also harmless.
935 // Otherwise we have a instruction that may not be safe.
939 // If Exiting block includes loop variant instructions then this
940 // loop may not be eliminated.
941 if (!safeExitingBlock(SD, ExitCondition->getParent()))
944 // Verify that loop exiting block has only two predecessor, where one predecessor
945 // is split condition block. The other predecessor will become exiting block's
946 // dominator after CFG is updated. TODO : Handle CFG's where exiting block has
947 // more then two predecessors. This requires extra work in updating dominator
949 BasicBlock *ExitingBBPred = NULL;
950 for (pred_iterator PI = pred_begin(ExitingBlock), PE = pred_end(ExitingBlock);
952 BasicBlock *BB = *PI;
953 if (SplitCondBlock == BB)
961 // Update loop bounds to absorb Op0 check.
962 updateLoopBounds(Op0);
963 // Update loop bounds to absorb Op1 check.
964 updateLoopBounds(Op1);
968 // Unconditionally connect split block to its remaining successor.
969 BranchInst *SplitTerminator =
970 cast<BranchInst>(SplitCondBlock->getTerminator());
971 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
972 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
973 if (Succ0 == ExitCondition->getParent())
974 SplitTerminator->setUnconditionalDest(Succ1);
976 SplitTerminator->setUnconditionalDest(Succ0);
978 // Remove split condition.
979 SD.SplitCondition->eraseFromParent();
980 if (Op0->use_begin() == Op0->use_end())
981 Op0->eraseFromParent();
982 if (Op1->use_begin() == Op1->use_end())
983 Op1->eraseFromParent();
985 BranchInst *ExitInsn =
986 dyn_cast<BranchInst>(ExitingBlock->getTerminator());
987 assert (ExitInsn && "Unable to find suitable loop exit branch");
988 BasicBlock *ExitBlock = ExitInsn->getSuccessor(1);
989 if (L->contains(ExitBlock))
990 ExitBlock = ExitInsn->getSuccessor(0);
992 // Update domiantor info. Now, ExitingBlock has only one predecessor,
993 // ExitingBBPred, and it is ExitingBlock's immediate domiantor.
994 DT->changeImmediateDominator(ExitingBlock, ExitingBBPred);
996 // If ExitingBlock is a member of loop BB's DF list then replace it with
997 // loop header and exit block.
998 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
1000 BasicBlock *BB = *I;
1001 if (BB == Header || BB == ExitingBlock)
1003 DominanceFrontier::iterator BBDF = DF->find(BB);
1004 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1005 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1006 while (DomSetI != DomSetE) {
1007 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1009 BasicBlock *DFBB = *CurrentItr;
1010 if (DFBB == ExitingBlock) {
1011 BBDF->second.erase(DFBB);
1012 BBDF->second.insert(Header);
1013 if (Header != ExitingBlock)
1014 BBDF->second.insert(ExitBlock);
1023 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
1024 /// This routine is used to remove split condition's dead branch, dominated by
1025 /// DeadBB. LiveBB dominates split conidition's other branch.
1026 void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
1027 BasicBlock *LiveBB) {
1029 // First update DeadBB's dominance frontier.
1030 SmallVector<BasicBlock *, 8> FrontierBBs;
1031 DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
1032 if (DeadBBDF != DF->end()) {
1033 SmallVector<BasicBlock *, 8> PredBlocks;
1035 DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
1036 for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
1037 DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
1038 BasicBlock *FrontierBB = *DeadBBSetI;
1039 FrontierBBs.push_back(FrontierBB);
1041 // Rremove any PHI incoming edge from blocks dominated by DeadBB.
1043 for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
1045 BasicBlock *P = *PI;
1046 if (P == DeadBB || DT->dominates(DeadBB, P))
1047 PredBlocks.push_back(P);
1050 for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
1051 FBI != FBE; ++FBI) {
1052 if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
1053 for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
1054 PE = PredBlocks.end(); PI != PE; ++PI) {
1055 BasicBlock *P = *PI;
1056 PN->removeIncomingValue(P);
1065 // Now remove DeadBB and all nodes dominated by DeadBB in df order.
1066 SmallVector<BasicBlock *, 32> WorkList;
1067 DomTreeNode *DN = DT->getNode(DeadBB);
1068 for (df_iterator<DomTreeNode*> DI = df_begin(DN),
1069 E = df_end(DN); DI != E; ++DI) {
1070 BasicBlock *BB = DI->getBlock();
1071 WorkList.push_back(BB);
1072 BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
1075 while (!WorkList.empty()) {
1076 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
1077 for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
1079 Instruction *I = BBI;
1081 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1082 I->eraseFromParent();
1084 LPM->deleteSimpleAnalysisValue(BB, LP);
1086 DF->removeBlock(BB);
1087 LI->removeBlock(BB);
1088 BB->eraseFromParent();
1091 // Update Frontier BBs' dominator info.
1092 while (!FrontierBBs.empty()) {
1093 BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
1094 BasicBlock *NewDominator = FBB->getSinglePredecessor();
1095 if (!NewDominator) {
1096 pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
1099 if (NewDominator != LiveBB) {
1100 for(; PI != PE; ++PI) {
1101 BasicBlock *P = *PI;
1103 NewDominator = LiveBB;
1106 NewDominator = DT->findNearestCommonDominator(NewDominator, P);
1110 assert (NewDominator && "Unable to fix dominator info.");
1111 DT->changeImmediateDominator(FBB, NewDominator);
1112 DF->changeImmediateDominator(FBB, NewDominator, DT);
1117 /// safeSplitCondition - Return true if it is possible to
1118 /// split loop using given split condition.
1119 bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
1121 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1122 BasicBlock *Latch = L->getLoopLatch();
1123 BranchInst *SplitTerminator =
1124 cast<BranchInst>(SplitCondBlock->getTerminator());
1125 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1126 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1128 // If split block does not dominate the latch then this is not a diamond.
1129 // Such loop may not benefit from index split.
1130 if (!DT->dominates(SplitCondBlock, Latch))
1133 // Finally this split condition is safe only if merge point for
1134 // split condition branch is loop latch. This check along with previous
1135 // check, to ensure that exit condition is in either loop latch or header,
1136 // filters all loops with non-empty loop body between merge point
1137 // and exit condition.
1138 DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
1139 assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
1140 if (Succ0DF->second.count(Latch))
1143 DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
1144 assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
1145 if (Succ1DF->second.count(Latch))
1151 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
1152 /// based on split value.
1153 void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
1155 ICmpInst *SC = cast<ICmpInst>(SD.SplitCondition);
1156 ICmpInst::Predicate SP = SC->getPredicate();
1157 const Type *Ty = SD.SplitValue->getType();
1158 bool Sign = ExitCondition->isSignedPredicate();
1159 BasicBlock *Preheader = L->getLoopPreheader();
1160 Instruction *PHTerminator = Preheader->getTerminator();
1162 // Initially use split value as upper loop bound for first loop and lower loop
1163 // bound for second loop.
1164 Value *AEV = SD.SplitValue;
1165 Value *BSV = SD.SplitValue;
1167 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
1168 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
1169 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
1170 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
1171 ExitCondition->swapOperands();
1178 switch (ExitCondition->getPredicate()) {
1179 case ICmpInst::ICMP_SGT:
1180 case ICmpInst::ICMP_UGT:
1181 case ICmpInst::ICMP_SGE:
1182 case ICmpInst::ICMP_UGE:
1184 assert (0 && "Unexpected exit condition predicate");
1186 case ICmpInst::ICMP_SLT:
1187 case ICmpInst::ICMP_ULT:
1190 case ICmpInst::ICMP_SLT:
1191 case ICmpInst::ICMP_ULT:
1193 // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
1195 // is transformed into
1197 // for (i = LB; i < min(UB, AEV); ++i)
1199 // for (i = max(LB, BSV); i < UB; ++i);
1202 case ICmpInst::ICMP_SLE:
1203 case ICmpInst::ICMP_ULE:
1206 // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
1208 // is transformed into
1212 // for (i = LB; i < min(UB, AEV); ++i)
1214 // for (i = max(LB, BSV); i < UB; ++i)
1216 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1217 ConstantInt::get(Ty, 1, Sign),
1218 "lsplit.add", PHTerminator);
1222 case ICmpInst::ICMP_SGE:
1223 case ICmpInst::ICMP_UGE:
1225 // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
1227 // is transformed into
1229 // for (i = LB; i < min(UB, AEV); ++i)
1231 // for (i = max(BSV, LB); i < UB; ++i)
1234 case ICmpInst::ICMP_SGT:
1235 case ICmpInst::ICMP_UGT:
1238 // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
1240 // is transformed into
1242 // BSV = AEV = SV + 1
1243 // for (i = LB; i < min(UB, AEV); ++i)
1245 // for (i = max(LB, BSV); i < UB; ++i)
1247 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1248 ConstantInt::get(Ty, 1, Sign),
1249 "lsplit.add", PHTerminator);
1254 assert (0 && "Unexpected split condition predicate");
1256 } // end switch (SP)
1259 case ICmpInst::ICMP_SLE:
1260 case ICmpInst::ICMP_ULE:
1263 case ICmpInst::ICMP_SLT:
1264 case ICmpInst::ICMP_ULT:
1266 // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
1268 // is transformed into
1271 // for (i = LB; i <= min(UB, AEV); ++i)
1273 // for (i = max(LB, BSV); i <= UB; ++i)
1275 AEV = BinaryOperator::CreateSub(SD.SplitValue,
1276 ConstantInt::get(Ty, 1, Sign),
1277 "lsplit.sub", PHTerminator);
1279 case ICmpInst::ICMP_SLE:
1280 case ICmpInst::ICMP_ULE:
1282 // for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; }
1284 // is transformed into
1287 // for (i = LB; i <= min(UB, AEV); ++i)
1289 // for (i = max(LB, BSV); i <= UB; ++i)
1291 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1292 ConstantInt::get(Ty, 1, Sign),
1293 "lsplit.add", PHTerminator);
1295 case ICmpInst::ICMP_SGT:
1296 case ICmpInst::ICMP_UGT:
1298 // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
1300 // is transformed into
1303 // for (i = LB; i <= min(AEV, UB); ++i)
1305 // for (i = max(LB, BSV); i <= UB; ++i)
1307 BSV = BinaryOperator::CreateAdd(SD.SplitValue,
1308 ConstantInt::get(Ty, 1, Sign),
1309 "lsplit.add", PHTerminator);
1311 case ICmpInst::ICMP_SGE:
1312 case ICmpInst::ICMP_UGE:
1315 // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
1317 // is transformed into
1320 // for (i = LB; i <= min(AEV, UB); ++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);
1329 assert (0 && "Unexpected split condition predicate");
1331 } // end switch (SP)
1336 // Calculate ALoop induction variable's new exiting value and
1337 // BLoop induction variable's new starting value. Calculuate these
1338 // values in original loop's preheader.
1339 // A_ExitValue = min(SplitValue, OrignalLoopExitValue)
1340 // B_StartValue = max(SplitValue, OriginalLoopStartValue)
1341 Instruction *InsertPt = L->getHeader()->getFirstNonPHI();
1343 // If ExitValue operand is also defined in Loop header then
1344 // insert new ExitValue after this operand definition.
1345 if (Instruction *EVN =
1346 dyn_cast<Instruction>(ExitCondition->getOperand(ExitValueNum))) {
1347 if (!isa<PHINode>(EVN))
1348 if (InsertPt->getParent() == EVN->getParent()) {
1349 BasicBlock::iterator LHBI = L->getHeader()->begin();
1350 BasicBlock::iterator LHBE = L->getHeader()->end();
1351 for(;LHBI != LHBE; ++LHBI) {
1352 Instruction *I = LHBI;
1359 Value *C1 = new ICmpInst(Sign ?
1360 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1362 ExitCondition->getOperand(ExitValueNum),
1363 "lsplit.ev", InsertPt);
1365 SD.A_ExitValue = SelectInst::Create(C1, AEV,
1366 ExitCondition->getOperand(ExitValueNum),
1367 "lsplit.ev", InsertPt);
1369 Value *C2 = new ICmpInst(Sign ?
1370 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1371 BSV, StartValue, "lsplit.sv",
1373 SD.B_StartValue = SelectInst::Create(C2, StartValue, BSV,
1374 "lsplit.sv", PHTerminator);
1377 /// splitLoop - Split current loop L in two loops using split information
1378 /// SD. Update dominator information. Maintain LCSSA form.
1379 bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
1381 if (!safeSplitCondition(SD))
1384 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1386 // Unable to handle triange loops at the moment.
1387 // In triangle loop, split condition is in header and one of the
1388 // the split destination is loop latch. If split condition is EQ
1389 // then such loops are already handle in processOneIterationLoop().
1390 BasicBlock *Latch = L->getLoopLatch();
1391 BranchInst *SplitTerminator =
1392 cast<BranchInst>(SplitCondBlock->getTerminator());
1393 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1394 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1395 if (L->getHeader() == SplitCondBlock
1396 && (Latch == Succ0 || Latch == Succ1))
1399 // If split condition branches heads do not have single predecessor,
1400 // SplitCondBlock, then is not possible to remove inactive branch.
1401 if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor())
1404 // If Exiting block includes loop variant instructions then this
1405 // loop may not be split safely.
1406 if (!safeExitingBlock(SD, ExitCondition->getParent()))
1409 // After loop is cloned there are two loops.
1411 // First loop, referred as ALoop, executes first part of loop's iteration
1412 // space split. Second loop, referred as BLoop, executes remaining
1413 // part of loop's iteration space.
1415 // ALoop's exit edge enters BLoop's header through a forwarding block which
1416 // acts as a BLoop's preheader.
1417 BasicBlock *Preheader = L->getLoopPreheader();
1419 // Calculate ALoop induction variable's new exiting value and
1420 // BLoop induction variable's new starting value.
1421 calculateLoopBounds(SD);
1424 DenseMap<const Value *, Value *> ValueMap;
1425 Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
1427 BasicBlock *B_Header = BLoop->getHeader();
1429 //[*] ALoop's exiting edge BLoop's header.
1430 // ALoop's original exit block becomes BLoop's exit block.
1431 PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
1432 BasicBlock *A_ExitingBlock = ExitCondition->getParent();
1433 BranchInst *A_ExitInsn =
1434 dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
1435 assert (A_ExitInsn && "Unable to find suitable loop exit branch");
1436 BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
1437 if (L->contains(B_ExitBlock)) {
1438 B_ExitBlock = A_ExitInsn->getSuccessor(0);
1439 A_ExitInsn->setSuccessor(0, B_Header);
1441 A_ExitInsn->setSuccessor(1, B_Header);
1443 //[*] Update ALoop's exit value using new exit value.
1444 ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
1446 // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
1447 // original loop's preheader. Add incoming PHINode values from
1448 // ALoop's exiting block. Update BLoop header's domiantor info.
1450 // Collect inverse map of Header PHINodes.
1451 DenseMap<Value *, Value *> InverseMap;
1452 for (BasicBlock::iterator BI = L->getHeader()->begin(),
1453 BE = L->getHeader()->end(); BI != BE; ++BI) {
1454 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1455 PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
1456 InverseMap[PNClone] = PN;
1461 for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1463 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1464 // Remove incoming value from original preheader.
1465 PN->removeIncomingValue(Preheader);
1467 // Add incoming value from A_ExitingBlock.
1469 PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
1471 PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
1473 // If loop header is also loop exiting block then
1474 // OrigPN is incoming value for B loop header.
1475 if (A_ExitingBlock == L->getHeader())
1478 V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
1479 PN->addIncoming(V2, A_ExitingBlock);
1484 DT->changeImmediateDominator(B_Header, A_ExitingBlock);
1485 DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
1487 // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
1488 // block. Remove incoming PHINode values from ALoop's exiting block.
1489 // Add new incoming values from BLoop's incoming exiting value.
1490 // Update BLoop exit block's dominator info..
1491 BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
1492 for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
1494 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1495 PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
1497 PN->removeIncomingValue(A_ExitingBlock);
1502 DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
1503 DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
1505 //[*] Split ALoop's exit edge. This creates a new block which
1506 // serves two purposes. First one is to hold PHINode defnitions
1507 // to ensure that ALoop's LCSSA form. Second use it to act
1508 // as a preheader for BLoop.
1509 BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
1511 //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
1512 // in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
1513 for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1515 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1516 Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
1517 PHINode *newPHI = PHINode::Create(PN->getType(), PN->getName());
1518 newPHI->addIncoming(V1, A_ExitingBlock);
1519 A_ExitBlock->getInstList().push_front(newPHI);
1520 PN->removeIncomingValue(A_ExitBlock);
1521 PN->addIncoming(newPHI, A_ExitBlock);
1526 //[*] Eliminate split condition's inactive branch from ALoop.
1527 BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
1528 BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
1529 BasicBlock *A_InactiveBranch = NULL;
1530 BasicBlock *A_ActiveBranch = NULL;
1531 if (SD.UseTrueBranchFirst) {
1532 A_ActiveBranch = A_BR->getSuccessor(0);
1533 A_InactiveBranch = A_BR->getSuccessor(1);
1535 A_ActiveBranch = A_BR->getSuccessor(1);
1536 A_InactiveBranch = A_BR->getSuccessor(0);
1538 A_BR->setUnconditionalDest(A_ActiveBranch);
1539 removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
1541 //[*] Eliminate split condition's inactive branch in from BLoop.
1542 BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
1543 BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
1544 BasicBlock *B_InactiveBranch = NULL;
1545 BasicBlock *B_ActiveBranch = NULL;
1546 if (SD.UseTrueBranchFirst) {
1547 B_ActiveBranch = B_BR->getSuccessor(1);
1548 B_InactiveBranch = B_BR->getSuccessor(0);
1550 B_ActiveBranch = B_BR->getSuccessor(0);
1551 B_InactiveBranch = B_BR->getSuccessor(1);
1553 B_BR->setUnconditionalDest(B_ActiveBranch);
1554 removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
1556 BasicBlock *A_Header = L->getHeader();
1557 if (A_ExitingBlock == A_Header)
1560 //[*] Move exit condition into split condition block to avoid
1561 // executing dead loop iteration.
1562 ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
1563 Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
1564 ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
1566 moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
1567 cast<ICmpInst>(SD.SplitCondition), IndVar, IndVarIncrement,
1570 moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
1571 B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
1576 // moveExitCondition - Move exit condition EC into split condition block CondBB.
1577 void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
1578 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
1579 PHINode *IV, Instruction *IVAdd, Loop *LP) {
1581 BasicBlock *ExitingBB = EC->getParent();
1582 Instruction *CurrentBR = CondBB->getTerminator();
1584 // Move exit condition into split condition block.
1585 EC->moveBefore(CurrentBR);
1586 EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
1588 // Move exiting block's branch into split condition block. Update its branch
1590 BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
1591 ExitingBR->moveBefore(CurrentBR);
1592 BasicBlock *OrigDestBB = NULL;
1593 if (ExitingBR->getSuccessor(0) == ExitBB) {
1594 OrigDestBB = ExitingBR->getSuccessor(1);
1595 ExitingBR->setSuccessor(1, ActiveBB);
1598 OrigDestBB = ExitingBR->getSuccessor(0);
1599 ExitingBR->setSuccessor(0, ActiveBB);
1602 // Remove split condition and current split condition branch.
1603 SC->eraseFromParent();
1604 CurrentBR->eraseFromParent();
1606 // Connect exiting block to original destination.
1607 BranchInst::Create(OrigDestBB, ExitingBB);
1610 updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd, LP);
1612 // Fix dominator info.
1613 // ExitBB is now dominated by CondBB
1614 DT->changeImmediateDominator(ExitBB, CondBB);
1615 DF->changeImmediateDominator(ExitBB, CondBB, DT);
1617 // Basicblocks dominated by ActiveBB may have ExitingBB or
1618 // a basic block outside the loop in their DF list. If so,
1619 // replace it with CondBB.
1620 DomTreeNode *Node = DT->getNode(ActiveBB);
1621 for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
1623 BasicBlock *BB = DI->getBlock();
1624 DominanceFrontier::iterator BBDF = DF->find(BB);
1625 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1626 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1627 while (DomSetI != DomSetE) {
1628 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1630 BasicBlock *DFBB = *CurrentItr;
1631 if (DFBB == ExitingBB || !L->contains(DFBB)) {
1632 BBDF->second.erase(DFBB);
1633 BBDF->second.insert(CondBB);
1639 /// updatePHINodes - CFG has been changed.
1641 /// - ExitBB's single predecessor was Latch
1642 /// - Latch's second successor was Header
1644 /// - ExitBB's single predecessor is Header
1645 /// - Latch's one and only successor is Header
1647 /// Update ExitBB PHINodes' to reflect this change.
1648 void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
1650 PHINode *IV, Instruction *IVIncrement,
1653 for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
1655 PHINode *PN = dyn_cast<PHINode>(BI);
1660 Value *V = PN->getIncomingValueForBlock(Latch);
1661 if (PHINode *PHV = dyn_cast<PHINode>(V)) {
1662 // PHV is in Latch. PHV has one use is in ExitBB PHINode. And one use
1663 // in Header which is new incoming value for PN.
1665 for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
1667 if (PHINode *U = dyn_cast<PHINode>(*UI))
1668 if (LP->contains(U->getParent())) {
1673 // Add incoming value from header only if PN has any use inside the loop.
1675 PN->addIncoming(NewV, Header);
1677 } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
1678 // If this instruction is IVIncrement then IV is new incoming value
1679 // from header otherwise this instruction must be incoming value from
1680 // header because loop is in LCSSA form.
1681 if (PHI == IVIncrement)
1682 PN->addIncoming(IV, Header);
1684 PN->addIncoming(V, Header);
1686 // Otherwise this is an incoming value from header because loop is in
1688 PN->addIncoming(V, Header);
1690 // Remove incoming value from Latch.
1691 PN->removeIncomingValue(Latch);