1 //===- LoopIndexSplit.cpp - Loop Index Splitting Pass ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Devang Patel and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements Loop Index Splitting Pass.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "loop-index-split"
16 #include "llvm/Transforms/Scalar.h"
17 #include "llvm/Analysis/LoopPass.h"
18 #include "llvm/Analysis/ScalarEvolutionExpander.h"
19 #include "llvm/Analysis/Dominators.h"
20 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
21 #include "llvm/Transforms/Utils/Cloning.h"
22 #include "llvm/Support/Compiler.h"
23 #include "llvm/ADT/DepthFirstIterator.h"
24 #include "llvm/ADT/Statistic.h"
28 STATISTIC(NumIndexSplit, "Number of loops index split");
32 class VISIBILITY_HIDDEN LoopIndexSplit : public LoopPass {
35 static char ID; // Pass ID, replacement for typeid
36 LoopIndexSplit() : LoopPass((intptr_t)&ID) {}
38 // Index split Loop L. Return true if loop is split.
39 bool runOnLoop(Loop *L, LPPassManager &LPM);
41 void getAnalysisUsage(AnalysisUsage &AU) const {
42 AU.addRequired<ScalarEvolution>();
43 AU.addPreserved<ScalarEvolution>();
44 AU.addRequiredID(LCSSAID);
45 AU.addPreservedID(LCSSAID);
46 AU.addRequired<LoopInfo>();
47 AU.addPreserved<LoopInfo>();
48 AU.addRequiredID(LoopSimplifyID);
49 AU.addPreservedID(LoopSimplifyID);
50 AU.addRequired<DominatorTree>();
51 AU.addRequired<DominanceFrontier>();
52 AU.addPreserved<DominatorTree>();
53 AU.addPreserved<DominanceFrontier>();
60 SplitInfo() : SplitValue(NULL), SplitCondition(NULL),
61 UseTrueBranchFirst(true), A_ExitValue(NULL),
64 // Induction variable's range is split at this value.
67 // This instruction compares IndVar against SplitValue.
68 Instruction *SplitCondition;
70 // True if after loop index split, first loop will execute split condition's
72 bool UseTrueBranchFirst;
74 // Exit value for first loop after loop split.
77 // Start value for second loop after loop split.
83 SplitCondition = NULL;
84 UseTrueBranchFirst = true;
93 // safeIcmpInst - CI is considered safe instruction if one of the operand
94 // is SCEVAddRecExpr based on induction variable and other operand is
95 // loop invariant. If CI is safe then populate SplitInfo object SD appropriately
97 bool safeICmpInst(ICmpInst *CI, SplitInfo &SD);
99 /// Find condition inside a loop that is suitable candidate for index split.
100 void findSplitCondition();
102 /// Find loop's exit condition.
103 void findLoopConditionals();
105 /// Return induction variable associated with value V.
106 void findIndVar(Value *V, Loop *L);
108 /// processOneIterationLoop - Current loop L contains compare instruction
109 /// that compares induction variable, IndVar, agains loop invariant. If
110 /// entire (i.e. meaningful) loop body is dominated by this compare
111 /// instruction then loop body is executed only for one iteration. In
112 /// such case eliminate loop structure surrounding this loop body. For
113 bool processOneIterationLoop(SplitInfo &SD);
115 void updateLoopBounds(ICmpInst *CI);
116 /// updateLoopIterationSpace - Current loop body is covered by an AND
117 /// instruction whose operands compares induction variables with loop
118 /// invariants. If possible, hoist this check outside the loop by
119 /// updating appropriate start and end values for induction variable.
120 bool updateLoopIterationSpace(SplitInfo &SD);
122 /// If loop header includes loop variant instruction operands then
123 /// this loop may not be eliminated.
124 bool safeHeader(SplitInfo &SD, BasicBlock *BB);
126 /// If Exiting block includes loop variant instructions then this
127 /// loop may not be eliminated.
128 bool safeExitingBlock(SplitInfo &SD, BasicBlock *BB);
130 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
131 /// This routine is used to remove split condition's dead branch, dominated by
132 /// DeadBB. LiveBB dominates split conidition's other branch.
133 void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB);
135 /// safeSplitCondition - Return true if it is possible to
136 /// split loop using given split condition.
137 bool safeSplitCondition(SplitInfo &SD);
139 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
140 /// based on split value.
141 void calculateLoopBounds(SplitInfo &SD);
143 /// updatePHINodes - CFG has been changed.
145 /// - ExitBB's single predecessor was Latch
146 /// - Latch's second successor was Header
148 /// - ExitBB's single predecessor was Header
149 /// - Latch's one and only successor was Header
151 /// Update ExitBB PHINodes' to reflect this change.
152 void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
154 PHINode *IV, Instruction *IVIncrement);
156 /// moveExitCondition - Move exit condition EC into split condition block CondBB.
157 void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
158 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
159 PHINode *IV, Instruction *IVAdd, Loop *LP);
161 /// splitLoop - Split current loop L in two loops using split information
162 /// SD. Update dominator information. Maintain LCSSA form.
163 bool splitLoop(SplitInfo &SD);
167 IndVarIncrement = NULL;
168 ExitCondition = NULL;
182 DominanceFrontier *DF;
183 SmallVector<SplitInfo, 4> SplitData;
185 // Induction variable whose range is being split by this transformation.
187 Instruction *IndVarIncrement;
189 // Loop exit condition.
190 ICmpInst *ExitCondition;
192 // Induction variable's initial value.
195 // Induction variable's final loop exit value operand number in exit condition..
196 unsigned ExitValueNum;
199 char LoopIndexSplit::ID = 0;
200 RegisterPass<LoopIndexSplit> X ("loop-index-split", "Index Split Loops");
203 LoopPass *llvm::createLoopIndexSplitPass() {
204 return new LoopIndexSplit();
207 // Index split Loop L. Return true if loop is split.
208 bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
209 bool Changed = false;
213 // FIXME - Nested loops make dominator info updates tricky.
214 if (!L->getSubLoops().empty())
217 SE = &getAnalysis<ScalarEvolution>();
218 DT = &getAnalysis<DominatorTree>();
219 LI = &getAnalysis<LoopInfo>();
220 DF = &getAnalysis<DominanceFrontier>();
224 findLoopConditionals();
229 findSplitCondition();
231 if (SplitData.empty())
234 // First see if it is possible to eliminate loop itself or not.
235 for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin(),
236 E = SplitData.end(); SI != E;) {
238 ICmpInst *CI = dyn_cast<ICmpInst>(SD.SplitCondition);
239 if (SD.SplitCondition->getOpcode() == Instruction::And) {
240 Changed = updateLoopIterationSpace(SD);
243 // If is loop is eliminated then nothing else to do here.
246 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
248 SplitData.erase(Delete_SI);
251 else if (CI && CI->getPredicate() == ICmpInst::ICMP_EQ) {
252 Changed = processOneIterationLoop(SD);
255 // If is loop is eliminated then nothing else to do here.
258 SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
260 SplitData.erase(Delete_SI);
266 if (SplitData.empty())
269 // Split most profitiable condition.
270 // FIXME : Implement cost analysis.
271 unsigned MostProfitableSDIndex = 0;
272 Changed = splitLoop(SplitData[MostProfitableSDIndex]);
280 /// Return true if V is a induction variable or induction variable's
281 /// increment for loop L.
282 void LoopIndexSplit::findIndVar(Value *V, Loop *L) {
284 Instruction *I = dyn_cast<Instruction>(V);
288 // Check if I is a phi node from loop header or not.
289 if (PHINode *PN = dyn_cast<PHINode>(V)) {
290 if (PN->getParent() == L->getHeader()) {
296 // Check if I is a add instruction whose one operand is
297 // phi node from loop header and second operand is constant.
298 if (I->getOpcode() != Instruction::Add)
301 Value *Op0 = I->getOperand(0);
302 Value *Op1 = I->getOperand(1);
304 if (PHINode *PN = dyn_cast<PHINode>(Op0)) {
305 if (PN->getParent() == L->getHeader()
306 && isa<ConstantInt>(Op1)) {
313 if (PHINode *PN = dyn_cast<PHINode>(Op1)) {
314 if (PN->getParent() == L->getHeader()
315 && isa<ConstantInt>(Op0)) {
325 // Find loop's exit condition and associated induction variable.
326 void LoopIndexSplit::findLoopConditionals() {
328 BasicBlock *ExitingBlock = NULL;
330 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
333 if (!L->isLoopExit(BB))
343 // If exiting block is neither loop header nor loop latch then this loop is
345 if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch())
348 // If exit block's terminator is conditional branch inst then we have found
350 BranchInst *BR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
351 if (!BR || BR->isUnconditional())
354 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
359 if (CI->getPredicate() == ICmpInst::ICMP_EQ
360 || CI->getPredicate() == ICmpInst::ICMP_NE)
365 // Exit condition's one operand is loop invariant exit value and second
366 // operand is SCEVAddRecExpr based on induction variable.
367 Value *V0 = CI->getOperand(0);
368 Value *V1 = CI->getOperand(1);
370 SCEVHandle SH0 = SE->getSCEV(V0);
371 SCEVHandle SH1 = SE->getSCEV(V1);
373 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
377 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
383 ExitCondition = NULL;
385 BasicBlock *Preheader = L->getLoopPreheader();
386 StartValue = IndVar->getIncomingValueForBlock(Preheader);
390 /// Find condition inside a loop that is suitable candidate for index split.
391 void LoopIndexSplit::findSplitCondition() {
394 // Check all basic block's terminators.
395 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
400 // If this basic block does not terminate in a conditional branch
401 // then terminator is not a suitable split condition.
402 BranchInst *BR = dyn_cast<BranchInst>(BB->getTerminator());
406 if (BR->isUnconditional())
409 if (Instruction *AndI = dyn_cast<Instruction>(BR->getCondition())) {
410 if (AndI->getOpcode() == Instruction::And) {
411 ICmpInst *Op0 = dyn_cast<ICmpInst>(AndI->getOperand(0));
412 ICmpInst *Op1 = dyn_cast<ICmpInst>(AndI->getOperand(1));
417 if (!safeICmpInst(Op0, SD))
420 if (!safeICmpInst(Op1, SD))
423 SD.SplitCondition = AndI;
424 SplitData.push_back(SD);
428 ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
429 if (!CI || CI == ExitCondition)
432 if (CI->getPredicate() == ICmpInst::ICMP_NE)
435 // If split condition predicate is GT or GE then first execute
436 // false branch of split condition.
437 if (CI->getPredicate() == ICmpInst::ICMP_UGT
438 || CI->getPredicate() == ICmpInst::ICMP_SGT
439 || CI->getPredicate() == ICmpInst::ICMP_UGE
440 || CI->getPredicate() == ICmpInst::ICMP_SGE)
441 SD.UseTrueBranchFirst = false;
443 // If one operand is loop invariant and second operand is SCEVAddRecExpr
444 // based on induction variable then CI is a candidate split condition.
445 if (safeICmpInst(CI, SD))
446 SplitData.push_back(SD);
450 // safeIcmpInst - CI is considered safe instruction if one of the operand
451 // is SCEVAddRecExpr based on induction variable and other operand is
452 // loop invariant. If CI is safe then populate SplitInfo object SD appropriately
454 bool LoopIndexSplit::safeICmpInst(ICmpInst *CI, SplitInfo &SD) {
456 Value *V0 = CI->getOperand(0);
457 Value *V1 = CI->getOperand(1);
459 SCEVHandle SH0 = SE->getSCEV(V0);
460 SCEVHandle SH1 = SE->getSCEV(V1);
462 if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
464 SD.SplitCondition = CI;
465 if (PHINode *PN = dyn_cast<PHINode>(V1)) {
469 else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
470 if (IndVarIncrement && IndVarIncrement == Insn)
474 else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
476 SD.SplitCondition = CI;
477 if (PHINode *PN = dyn_cast<PHINode>(V0)) {
481 else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
482 if (IndVarIncrement && IndVarIncrement == Insn)
490 /// processOneIterationLoop - Current loop L contains compare instruction
491 /// that compares induction variable, IndVar, against loop invariant. If
492 /// entire (i.e. meaningful) loop body is dominated by this compare
493 /// instruction then loop body is executed only once. In such case eliminate
494 /// loop structure surrounding this loop body. For example,
495 /// for (int i = start; i < end; ++i) {
496 /// if ( i == somevalue) {
500 /// can be transformed into
501 /// if (somevalue >= start && somevalue < end) {
505 bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
507 BasicBlock *Header = L->getHeader();
509 // First of all, check if SplitCondition dominates entire loop body
512 // If SplitCondition is not in loop header then this loop is not suitable
513 // for this transformation.
514 if (SD.SplitCondition->getParent() != Header)
517 // If loop header includes loop variant instruction operands then
518 // this loop may not be eliminated.
519 if (!safeHeader(SD, Header))
522 // If Exiting block includes loop variant instructions then this
523 // loop may not be eliminated.
524 if (!safeExitingBlock(SD, ExitCondition->getParent()))
527 // Filter loops where split condition's false branch is not empty.
528 if (ExitCondition->getParent() != Header->getTerminator()->getSuccessor(1))
531 // If split condition is not safe then do not process this loop.
533 // for(int i = 0; i < N; i++) {
542 if (!safeSplitCondition(SD))
545 BasicBlock *Latch = L->getLoopLatch();
546 BranchInst *BR = dyn_cast<BranchInst>(Latch->getTerminator());
552 // Replace index variable with split value in loop body. Loop body is executed
553 // only when index variable is equal to split value.
554 IndVar->replaceAllUsesWith(SD.SplitValue);
556 // Remove Latch to Header edge.
557 BasicBlock *LatchSucc = NULL;
558 Header->removePredecessor(Latch);
559 for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
564 BR->setUnconditionalDest(LatchSucc);
566 Instruction *Terminator = Header->getTerminator();
567 Value *ExitValue = ExitCondition->getOperand(ExitValueNum);
569 // Replace split condition in header.
571 // SplitCondition : icmp eq i32 IndVar, SplitValue
573 // c1 = icmp uge i32 SplitValue, StartValue
574 // c2 = icmp ult i32 SplitValue, ExitValue
576 bool SignedPredicate = ExitCondition->isSignedPredicate();
577 Instruction *C1 = new ICmpInst(SignedPredicate ?
578 ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
579 SD.SplitValue, StartValue, "lisplit",
581 Instruction *C2 = new ICmpInst(SignedPredicate ?
582 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
583 SD.SplitValue, ExitValue, "lisplit",
585 Instruction *NSplitCond = BinaryOperator::createAnd(C1, C2, "lisplit",
587 SD.SplitCondition->replaceAllUsesWith(NSplitCond);
588 SD.SplitCondition->eraseFromParent();
590 // Now, clear latch block. Remove instructions that are responsible
591 // to increment induction variable.
592 Instruction *LTerminator = Latch->getTerminator();
593 for (BasicBlock::iterator LB = Latch->begin(), LE = Latch->end();
597 if (isa<PHINode>(I) || I == LTerminator)
600 if (I == IndVarIncrement)
601 I->replaceAllUsesWith(ExitValue);
603 I->replaceAllUsesWith(UndefValue::get(I->getType()));
604 I->eraseFromParent();
607 LPM->deleteLoopFromQueue(L);
609 // Update Dominator Info.
610 // Only CFG change done is to remove Latch to Header edge. This
611 // does not change dominator tree because Latch did not dominate
614 DominanceFrontier::iterator HeaderDF = DF->find(Header);
615 if (HeaderDF != DF->end())
616 DF->removeFromFrontier(HeaderDF, Header);
618 DominanceFrontier::iterator LatchDF = DF->find(Latch);
619 if (LatchDF != DF->end())
620 DF->removeFromFrontier(LatchDF, Header);
625 // If loop header includes loop variant instruction operands then
626 // this loop can not be eliminated. This is used by processOneIterationLoop().
627 bool LoopIndexSplit::safeHeader(SplitInfo &SD, BasicBlock *Header) {
629 Instruction *Terminator = Header->getTerminator();
630 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
638 // SplitCondition itself is OK.
639 if (I == SD.SplitCondition)
642 // Induction variable is OK.
646 // Induction variable increment is OK.
647 if (I == IndVarIncrement)
650 // Terminator is also harmless.
654 // Otherwise we have a instruction that may not be safe.
661 // If Exiting block includes loop variant instructions then this
662 // loop may not be eliminated. This is used by processOneIterationLoop().
663 bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD,
664 BasicBlock *ExitingBlock) {
666 for (BasicBlock::iterator BI = ExitingBlock->begin(),
667 BE = ExitingBlock->end(); BI != BE; ++BI) {
674 // Induction variable increment is OK.
675 if (IndVarIncrement && IndVarIncrement == I)
678 // Check if I is induction variable increment instruction.
679 if (!IndVarIncrement && I->getOpcode() == Instruction::Add) {
681 Value *Op0 = I->getOperand(0);
682 Value *Op1 = I->getOperand(1);
684 ConstantInt *CI = NULL;
686 if ((PN = dyn_cast<PHINode>(Op0))) {
687 if ((CI = dyn_cast<ConstantInt>(Op1)))
690 if ((PN = dyn_cast<PHINode>(Op1))) {
691 if ((CI = dyn_cast<ConstantInt>(Op0)))
695 if (IndVarIncrement && PN == IndVar && CI->isOne())
699 // I is an Exit condition if next instruction is block terminator.
700 // Exit condition is OK if it compares loop invariant exit value,
701 // which is checked below.
702 else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
703 if (EC == ExitCondition)
707 if (I == ExitingBlock->getTerminator())
710 // Otherwise we have instruction that may not be safe.
714 // We could not find any reason to consider ExitingBlock unsafe.
718 void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) {
720 Value *V0 = CI->getOperand(0);
721 Value *V1 = CI->getOperand(1);
724 SCEVHandle SH0 = SE->getSCEV(V0);
726 if (SH0->isLoopInvariant(L))
731 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
732 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
733 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
734 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
735 ExitCondition->swapOperands();
744 Value *UB = ExitCondition->getOperand(ExitValueNum);
745 const Type *Ty = NV->getType();
746 bool Sign = ExitCondition->isSignedPredicate();
747 BasicBlock *Preheader = L->getLoopPreheader();
748 Instruction *PHTerminator = Preheader->getTerminator();
750 assert (NV && "Unexpected value");
752 switch (CI->getPredicate()) {
753 case ICmpInst::ICMP_ULE:
754 case ICmpInst::ICMP_SLE:
755 // for (i = LB; i < UB; ++i)
756 // if (i <= NV && ...)
759 // is transformed into
760 // NUB = min (NV+1, UB)
761 // for (i = LB; i < NUB ; ++i)
764 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
765 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
766 Value *A = BinaryOperator::createAdd(NV, ConstantInt::get(Ty, 1, Sign),
767 "lsplit.add", PHTerminator);
768 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
769 A, UB,"lsplit,c", PHTerminator);
770 NUB = new SelectInst (C, A, UB, "lsplit.nub", PHTerminator);
773 // for (i = LB; i <= UB; ++i)
774 // if (i <= NV && ...)
777 // is transformed into
778 // NUB = min (NV, UB)
779 // for (i = LB; i <= NUB ; ++i)
782 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
783 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
784 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
785 NV, UB, "lsplit.c", PHTerminator);
786 NUB = new SelectInst (C, NV, UB, "lsplit.nub", PHTerminator);
789 case ICmpInst::ICMP_ULT:
790 case ICmpInst::ICMP_SLT:
791 // for (i = LB; i < UB; ++i)
792 // if (i < NV && ...)
795 // is transformed into
796 // NUB = min (NV, UB)
797 // for (i = LB; i < NUB ; ++i)
800 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
801 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
802 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
803 NV, UB, "lsplit.c", PHTerminator);
804 NUB = new SelectInst (C, NV, UB, "lsplit.nub", PHTerminator);
807 // for (i = LB; i <= UB; ++i)
808 // if (i < NV && ...)
811 // is transformed into
812 // NUB = min (NV -1 , UB)
813 // for (i = LB; i <= NUB ; ++i)
816 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
817 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
818 Value *S = BinaryOperator::createSub(NV, ConstantInt::get(Ty, 1, Sign),
819 "lsplit.add", PHTerminator);
820 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
821 S, UB, "lsplit.c", PHTerminator);
822 NUB = new SelectInst (C, S, UB, "lsplit.nub", PHTerminator);
825 case ICmpInst::ICMP_UGE:
826 case ICmpInst::ICMP_SGE:
827 // for (i = LB; i (< or <=) UB; ++i)
828 // if (i >= NV && ...)
831 // is transformed into
832 // NLB = max (NV, LB)
833 // for (i = NLB; i (< or <=) UB ; ++i)
837 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
838 NV, StartValue, "lsplit.c", PHTerminator);
839 NLB = new SelectInst (C, StartValue, NV, "lsplit.nlb", PHTerminator);
842 case ICmpInst::ICMP_UGT:
843 case ICmpInst::ICMP_SGT:
844 // for (i = LB; i (< or <=) UB; ++i)
845 // if (i > NV && ...)
848 // is transformed into
849 // NLB = max (NV+1, LB)
850 // for (i = NLB; i (< or <=) UB ; ++i)
854 Value *A = BinaryOperator::createAdd(NV, ConstantInt::get(Ty, 1, Sign),
855 "lsplit.add", PHTerminator);
856 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
857 A, StartValue, "lsplit.c", PHTerminator);
858 NLB = new SelectInst (C, StartValue, A, "lsplit.nlb", PHTerminator);
862 assert ( 0 && "Unexpected split condition predicate");
866 unsigned i = IndVar->getBasicBlockIndex(Preheader);
867 IndVar->setIncomingValue(i, NLB);
871 ExitCondition->setOperand(ExitValueNum, NUB);
874 /// updateLoopIterationSpace - Current loop body is covered by an AND
875 /// instruction whose operands compares induction variables with loop
876 /// invariants. If possible, hoist this check outside the loop by
877 /// updating appropriate start and end values for induction variable.
878 bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) {
879 BasicBlock *Header = L->getHeader();
880 BasicBlock *ExitingBlock = ExitCondition->getParent();
881 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
883 ICmpInst *Op0 = cast<ICmpInst>(SD.SplitCondition->getOperand(0));
884 ICmpInst *Op1 = cast<ICmpInst>(SD.SplitCondition->getOperand(1));
886 if (Op0->getPredicate() == ICmpInst::ICMP_EQ
887 || Op0->getPredicate() == ICmpInst::ICMP_NE
888 || Op0->getPredicate() == ICmpInst::ICMP_EQ
889 || Op0->getPredicate() == ICmpInst::ICMP_NE)
892 // Check if SplitCondition dominates entire loop body
895 // If SplitCondition is not in loop header then this loop is not suitable
896 // for this transformation.
897 if (SD.SplitCondition->getParent() != Header)
900 // If loop header includes loop variant instruction operands then
901 // this loop may not be eliminated.
902 Instruction *Terminator = Header->getTerminator();
903 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
911 // SplitCondition itself is OK.
912 if (I == SD.SplitCondition)
914 if (I == Op0 || I == Op1)
917 // Induction variable is OK.
921 // Induction variable increment is OK.
922 if (I == IndVarIncrement)
925 // Terminator is also harmless.
929 // Otherwise we have a instruction that may not be safe.
933 // If Exiting block includes loop variant instructions then this
934 // loop may not be eliminated.
935 if (!safeExitingBlock(SD, ExitCondition->getParent()))
938 // Verify that loop exiting block has only two predecessor, where one predecessor
939 // is split condition block. The other predecessor will become exiting block's
940 // dominator after CFG is updated. TODO : Handle CFG's where exiting block has
941 // more then two predecessors. This requires extra work in updating dominator
943 BasicBlock *ExitingBBPred = NULL;
944 for (pred_iterator PI = pred_begin(ExitingBlock), PE = pred_end(ExitingBlock);
946 BasicBlock *BB = *PI;
947 if (SplitCondBlock == BB)
955 // Update loop bounds to absorb Op0 check.
956 updateLoopBounds(Op0);
957 // Update loop bounds to absorb Op1 check.
958 updateLoopBounds(Op1);
962 // Unconditionally connect split block to its remaining successor.
963 BranchInst *SplitTerminator =
964 cast<BranchInst>(SplitCondBlock->getTerminator());
965 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
966 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
967 if (Succ0 == ExitCondition->getParent())
968 SplitTerminator->setUnconditionalDest(Succ1);
970 SplitTerminator->setUnconditionalDest(Succ0);
972 // Remove split condition.
973 SD.SplitCondition->eraseFromParent();
974 if (Op0->use_begin() == Op0->use_end())
975 Op0->eraseFromParent();
976 if (Op1->use_begin() == Op1->use_end())
977 Op1->eraseFromParent();
979 BranchInst *ExitInsn =
980 dyn_cast<BranchInst>(ExitingBlock->getTerminator());
981 assert (ExitInsn && "Unable to find suitable loop exit branch");
982 BasicBlock *ExitBlock = ExitInsn->getSuccessor(1);
983 if (L->contains(ExitBlock))
984 ExitBlock = ExitInsn->getSuccessor(0);
986 // Update domiantor info. Now, ExitingBlock has only one predecessor,
987 // ExitingBBPred, and it is ExitingBlock's immediate domiantor.
988 DT->changeImmediateDominator(ExitingBlock, ExitingBBPred);
990 // If ExitingBlock is a member of loop BB's DF list then replace it with
991 // loop header and exit block.
992 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
995 if (BB == Header || BB == ExitingBlock)
997 DominanceFrontier::iterator BBDF = DF->find(BB);
998 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
999 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1000 while (DomSetI != DomSetE) {
1001 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1003 BasicBlock *DFBB = *CurrentItr;
1004 if (DFBB == ExitingBlock) {
1005 BBDF->second.erase(DFBB);
1006 BBDF->second.insert(Header);
1007 if (Header != ExitingBlock)
1008 BBDF->second.insert(ExitBlock);
1017 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
1018 /// This routine is used to remove split condition's dead branch, dominated by
1019 /// DeadBB. LiveBB dominates split conidition's other branch.
1020 void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
1021 BasicBlock *LiveBB) {
1023 // First update DeadBB's dominance frontier.
1024 SmallVector<BasicBlock *, 8> FrontierBBs;
1025 DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
1026 if (DeadBBDF != DF->end()) {
1027 SmallVector<BasicBlock *, 8> PredBlocks;
1029 DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
1030 for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
1031 DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
1032 BasicBlock *FrontierBB = *DeadBBSetI;
1033 FrontierBBs.push_back(FrontierBB);
1035 // Rremove any PHI incoming edge from blocks dominated by DeadBB.
1037 for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
1039 BasicBlock *P = *PI;
1040 if (P == DeadBB || DT->dominates(DeadBB, P))
1041 PredBlocks.push_back(P);
1044 for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
1045 FBI != FBE; ++FBI) {
1046 if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
1047 for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
1048 PE = PredBlocks.end(); PI != PE; ++PI) {
1049 BasicBlock *P = *PI;
1050 PN->removeIncomingValue(P);
1059 // Now remove DeadBB and all nodes dominated by DeadBB in df order.
1060 SmallVector<BasicBlock *, 32> WorkList;
1061 DomTreeNode *DN = DT->getNode(DeadBB);
1062 for (df_iterator<DomTreeNode*> DI = df_begin(DN),
1063 E = df_end(DN); DI != E; ++DI) {
1064 BasicBlock *BB = DI->getBlock();
1065 WorkList.push_back(BB);
1066 BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
1069 while (!WorkList.empty()) {
1070 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
1071 for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
1073 Instruction *I = BBI;
1075 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1076 I->eraseFromParent();
1078 LPM->deleteSimpleAnalysisValue(BB, LP);
1080 DF->removeBlock(BB);
1081 LI->removeBlock(BB);
1082 BB->eraseFromParent();
1085 // Update Frontier BBs' dominator info.
1086 while (!FrontierBBs.empty()) {
1087 BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
1088 BasicBlock *NewDominator = FBB->getSinglePredecessor();
1089 if (!NewDominator) {
1090 pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
1093 if (NewDominator != LiveBB) {
1094 for(; PI != PE; ++PI) {
1095 BasicBlock *P = *PI;
1097 NewDominator = LiveBB;
1100 NewDominator = DT->findNearestCommonDominator(NewDominator, P);
1104 assert (NewDominator && "Unable to fix dominator info.");
1105 DT->changeImmediateDominator(FBB, NewDominator);
1106 DF->changeImmediateDominator(FBB, NewDominator, DT);
1111 /// safeSplitCondition - Return true if it is possible to
1112 /// split loop using given split condition.
1113 bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
1115 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1116 BasicBlock *Latch = L->getLoopLatch();
1117 BranchInst *SplitTerminator =
1118 cast<BranchInst>(SplitCondBlock->getTerminator());
1119 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1120 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1122 // Finally this split condition is safe only if merge point for
1123 // split condition branch is loop latch. This check along with previous
1124 // check, to ensure that exit condition is in either loop latch or header,
1125 // filters all loops with non-empty loop body between merge point
1126 // and exit condition.
1127 DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
1128 assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
1129 if (Succ0DF->second.count(Latch))
1132 DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
1133 assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
1134 if (Succ1DF->second.count(Latch))
1140 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
1141 /// based on split value.
1142 void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
1144 ICmpInst *SC = cast<ICmpInst>(SD.SplitCondition);
1145 ICmpInst::Predicate SP = SC->getPredicate();
1146 const Type *Ty = SD.SplitValue->getType();
1147 bool Sign = ExitCondition->isSignedPredicate();
1148 BasicBlock *Preheader = L->getLoopPreheader();
1149 Instruction *PHTerminator = Preheader->getTerminator();
1151 // Initially use split value as upper loop bound for first loop and lower loop
1152 // bound for second loop.
1153 Value *AEV = SD.SplitValue;
1154 Value *BSV = SD.SplitValue;
1156 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
1157 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
1158 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
1159 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE)
1160 ExitCondition->swapOperands();
1162 switch (ExitCondition->getPredicate()) {
1163 case ICmpInst::ICMP_SGT:
1164 case ICmpInst::ICMP_UGT:
1165 case ICmpInst::ICMP_SGE:
1166 case ICmpInst::ICMP_UGE:
1168 assert (0 && "Unexpected exit condition predicate");
1170 case ICmpInst::ICMP_SLT:
1171 case ICmpInst::ICMP_ULT:
1174 case ICmpInst::ICMP_SLT:
1175 case ICmpInst::ICMP_ULT:
1177 // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
1179 // is transformed into
1181 // for (i = LB; i < min(UB, AEV); ++i)
1183 // for (i = max(LB, BSV); i < UB; ++i);
1186 case ICmpInst::ICMP_SLE:
1187 case ICmpInst::ICMP_ULE:
1190 // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
1192 // is transformed into
1196 // for (i = LB; i < min(UB, AEV); ++i)
1198 // for (i = max(LB, BSV); i < UB; ++i)
1200 BSV = BinaryOperator::createAdd(SD.SplitValue,
1201 ConstantInt::get(Ty, 1, Sign),
1202 "lsplit.add", PHTerminator);
1206 case ICmpInst::ICMP_SGE:
1207 case ICmpInst::ICMP_UGE:
1209 // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
1211 // is transformed into
1213 // for (i = LB; i < min(UB, AEV); ++i)
1215 // for (i = max(BSV, LB); i < UB; ++i)
1218 case ICmpInst::ICMP_SGT:
1219 case ICmpInst::ICMP_UGT:
1222 // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
1224 // is transformed into
1226 // BSV = AEV = SV + 1
1227 // for (i = LB; i < min(UB, AEV); ++i)
1229 // for (i = max(LB, BSV); i < UB; ++i)
1231 BSV = BinaryOperator::createAdd(SD.SplitValue,
1232 ConstantInt::get(Ty, 1, Sign),
1233 "lsplit.add", PHTerminator);
1238 assert (0 && "Unexpected split condition predicate");
1240 } // end switch (SP)
1243 case ICmpInst::ICMP_SLE:
1244 case ICmpInst::ICMP_ULE:
1247 case ICmpInst::ICMP_SLT:
1248 case ICmpInst::ICMP_ULT:
1250 // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
1252 // is transformed into
1255 // for (i = LB; i <= min(UB, AEV); ++i)
1257 // for (i = max(LB, BSV); i <= UB; ++i)
1259 AEV = BinaryOperator::createSub(SD.SplitValue,
1260 ConstantInt::get(Ty, 1, Sign),
1261 "lsplit.sub", PHTerminator);
1263 case ICmpInst::ICMP_SLE:
1264 case ICmpInst::ICMP_ULE:
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 BSV = BinaryOperator::createAdd(SD.SplitValue,
1276 ConstantInt::get(Ty, 1, Sign),
1277 "lsplit.add", PHTerminator);
1279 case ICmpInst::ICMP_SGT:
1280 case ICmpInst::ICMP_UGT:
1282 // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
1284 // is transformed into
1287 // for (i = LB; i <= min(AEV, UB); ++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_SGE:
1296 case ICmpInst::ICMP_UGE:
1299 // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
1301 // is transformed into
1304 // for (i = LB; i <= min(AEV, UB); ++i)
1306 // for (i = max(LB, BSV); i <= UB; ++i)
1308 AEV = BinaryOperator::createSub(SD.SplitValue,
1309 ConstantInt::get(Ty, 1, Sign),
1310 "lsplit.sub", PHTerminator);
1313 assert (0 && "Unexpected split condition predicate");
1315 } // end switch (SP)
1320 // Calculate ALoop induction variable's new exiting value and
1321 // BLoop induction variable's new starting value. Calculuate these
1322 // values in original loop's preheader.
1323 // A_ExitValue = min(SplitValue, OrignalLoopExitValue)
1324 // B_StartValue = max(SplitValue, OriginalLoopStartValue)
1325 Instruction *InsertPt = L->getHeader()->getFirstNonPHI();
1326 Value *C1 = new ICmpInst(Sign ?
1327 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1329 ExitCondition->getOperand(ExitValueNum),
1330 "lsplit.ev", InsertPt);
1332 SD.A_ExitValue = new SelectInst(C1, AEV,
1333 ExitCondition->getOperand(ExitValueNum),
1334 "lsplit.ev", InsertPt);
1336 Value *C2 = new ICmpInst(Sign ?
1337 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1338 BSV, StartValue, "lsplit.sv",
1340 SD.B_StartValue = new SelectInst(C2, StartValue, BSV,
1341 "lsplit.sv", PHTerminator);
1344 /// splitLoop - Split current loop L in two loops using split information
1345 /// SD. Update dominator information. Maintain LCSSA form.
1346 bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
1348 if (!safeSplitCondition(SD))
1351 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1353 // Unable to handle triange loops at the moment.
1354 // In triangle loop, split condition is in header and one of the
1355 // the split destination is loop latch. If split condition is EQ
1356 // then such loops are already handle in processOneIterationLoop().
1357 BasicBlock *Latch = L->getLoopLatch();
1358 BranchInst *SplitTerminator =
1359 cast<BranchInst>(SplitCondBlock->getTerminator());
1360 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1361 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1362 if (L->getHeader() == SplitCondBlock
1363 && (Latch == Succ0 || Latch == Succ1))
1366 // If split condition branches heads do not have single predecessor,
1367 // SplitCondBlock, then is not possible to remove inactive branch.
1368 if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor())
1371 // After loop is cloned there are two loops.
1373 // First loop, referred as ALoop, executes first part of loop's iteration
1374 // space split. Second loop, referred as BLoop, executes remaining
1375 // part of loop's iteration space.
1377 // ALoop's exit edge enters BLoop's header through a forwarding block which
1378 // acts as a BLoop's preheader.
1379 BasicBlock *Preheader = L->getLoopPreheader();
1381 // Calculate ALoop induction variable's new exiting value and
1382 // BLoop induction variable's new starting value.
1383 calculateLoopBounds(SD);
1386 DenseMap<const Value *, Value *> ValueMap;
1387 Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
1389 BasicBlock *B_Header = BLoop->getHeader();
1391 //[*] ALoop's exiting edge BLoop's header.
1392 // ALoop's original exit block becomes BLoop's exit block.
1393 PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
1394 BasicBlock *A_ExitingBlock = ExitCondition->getParent();
1395 BranchInst *A_ExitInsn =
1396 dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
1397 assert (A_ExitInsn && "Unable to find suitable loop exit branch");
1398 BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
1399 if (L->contains(B_ExitBlock)) {
1400 B_ExitBlock = A_ExitInsn->getSuccessor(0);
1401 A_ExitInsn->setSuccessor(0, B_Header);
1403 A_ExitInsn->setSuccessor(1, B_Header);
1405 //[*] Update ALoop's exit value using new exit value.
1406 ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
1408 // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
1409 // original loop's preheader. Add incoming PHINode values from
1410 // ALoop's exiting block. Update BLoop header's domiantor info.
1412 // Collect inverse map of Header PHINodes.
1413 DenseMap<Value *, Value *> InverseMap;
1414 for (BasicBlock::iterator BI = L->getHeader()->begin(),
1415 BE = L->getHeader()->end(); BI != BE; ++BI) {
1416 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1417 PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
1418 InverseMap[PNClone] = PN;
1423 for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1425 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1426 // Remove incoming value from original preheader.
1427 PN->removeIncomingValue(Preheader);
1429 // Add incoming value from A_ExitingBlock.
1431 PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
1433 PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
1434 Value *V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
1435 PN->addIncoming(V2, A_ExitingBlock);
1440 DT->changeImmediateDominator(B_Header, A_ExitingBlock);
1441 DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
1443 // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
1444 // block. Remove incoming PHINode values from ALoop's exiting block.
1445 // Add new incoming values from BLoop's incoming exiting value.
1446 // Update BLoop exit block's dominator info..
1447 BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
1448 for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
1450 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1451 PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
1453 PN->removeIncomingValue(A_ExitingBlock);
1458 DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
1459 DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
1461 //[*] Split ALoop's exit edge. This creates a new block which
1462 // serves two purposes. First one is to hold PHINode defnitions
1463 // to ensure that ALoop's LCSSA form. Second use it to act
1464 // as a preheader for BLoop.
1465 BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
1467 //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
1468 // in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
1469 for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1471 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1472 Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
1473 PHINode *newPHI = new PHINode(PN->getType(), PN->getName());
1474 newPHI->addIncoming(V1, A_ExitingBlock);
1475 A_ExitBlock->getInstList().push_front(newPHI);
1476 PN->removeIncomingValue(A_ExitBlock);
1477 PN->addIncoming(newPHI, A_ExitBlock);
1482 //[*] Eliminate split condition's inactive branch from ALoop.
1483 BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
1484 BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
1485 BasicBlock *A_InactiveBranch = NULL;
1486 BasicBlock *A_ActiveBranch = NULL;
1487 if (SD.UseTrueBranchFirst) {
1488 A_ActiveBranch = A_BR->getSuccessor(0);
1489 A_InactiveBranch = A_BR->getSuccessor(1);
1491 A_ActiveBranch = A_BR->getSuccessor(1);
1492 A_InactiveBranch = A_BR->getSuccessor(0);
1494 A_BR->setUnconditionalDest(A_ActiveBranch);
1495 removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
1497 //[*] Eliminate split condition's inactive branch in from BLoop.
1498 BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
1499 BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
1500 BasicBlock *B_InactiveBranch = NULL;
1501 BasicBlock *B_ActiveBranch = NULL;
1502 if (SD.UseTrueBranchFirst) {
1503 B_ActiveBranch = B_BR->getSuccessor(1);
1504 B_InactiveBranch = B_BR->getSuccessor(0);
1506 B_ActiveBranch = B_BR->getSuccessor(0);
1507 B_InactiveBranch = B_BR->getSuccessor(1);
1509 B_BR->setUnconditionalDest(B_ActiveBranch);
1510 removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
1512 BasicBlock *A_Header = L->getHeader();
1513 if (A_ExitingBlock == A_Header)
1516 //[*] Move exit condition into split condition block to avoid
1517 // executing dead loop iteration.
1518 ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
1519 Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
1520 ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
1522 moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
1523 cast<ICmpInst>(SD.SplitCondition), IndVar, IndVarIncrement,
1526 moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
1527 B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
1532 // moveExitCondition - Move exit condition EC into split condition block CondBB.
1533 void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
1534 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
1535 PHINode *IV, Instruction *IVAdd, Loop *LP) {
1537 BasicBlock *ExitingBB = EC->getParent();
1538 Instruction *CurrentBR = CondBB->getTerminator();
1540 // Move exit condition into split condition block.
1541 EC->moveBefore(CurrentBR);
1542 EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
1544 // Move exiting block's branch into split condition block. Update its branch
1546 BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
1547 ExitingBR->moveBefore(CurrentBR);
1548 if (ExitingBR->getSuccessor(0) == ExitBB)
1549 ExitingBR->setSuccessor(1, ActiveBB);
1551 ExitingBR->setSuccessor(0, ActiveBB);
1553 // Remove split condition and current split condition branch.
1554 SC->eraseFromParent();
1555 CurrentBR->eraseFromParent();
1557 // Connect exiting block to split condition block.
1558 new BranchInst(CondBB, ExitingBB);
1561 updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd);
1563 // Fix dominator info.
1564 // ExitBB is now dominated by CondBB
1565 DT->changeImmediateDominator(ExitBB, CondBB);
1566 DF->changeImmediateDominator(ExitBB, CondBB, DT);
1568 // Basicblocks dominated by ActiveBB may have ExitingBB or
1569 // a basic block outside the loop in their DF list. If so,
1570 // replace it with CondBB.
1571 DomTreeNode *Node = DT->getNode(ActiveBB);
1572 for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
1574 BasicBlock *BB = DI->getBlock();
1575 DominanceFrontier::iterator BBDF = DF->find(BB);
1576 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1577 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1578 while (DomSetI != DomSetE) {
1579 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1581 BasicBlock *DFBB = *CurrentItr;
1582 if (DFBB == ExitingBB || !L->contains(DFBB)) {
1583 BBDF->second.erase(DFBB);
1584 BBDF->second.insert(CondBB);
1590 /// updatePHINodes - CFG has been changed.
1592 /// - ExitBB's single predecessor was Latch
1593 /// - Latch's second successor was Header
1595 /// - ExitBB's single predecessor was Header
1596 /// - Latch's one and only successor was Header
1598 /// Update ExitBB PHINodes' to reflect this change.
1599 void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
1601 PHINode *IV, Instruction *IVIncrement) {
1603 for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
1605 PHINode *PN = dyn_cast<PHINode>(BI);
1609 Value *V = PN->getIncomingValueForBlock(Latch);
1610 if (PHINode *PHV = dyn_cast<PHINode>(V)) {
1611 // PHV is in Latch. PHV has two uses, one use is in ExitBB PHINode
1613 // The second use is in Header and it is new incoming value for PN.
1617 for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
1620 U1 = cast<PHINode>(*UI);
1622 U2 = cast<PHINode>(*UI);
1624 assert ( 0 && "Unexpected third use of this PHINode");
1626 assert (U1 && U2 && "Unable to find two uses");
1628 if (U1->getParent() == Header)
1632 PN->addIncoming(NewV, Header);
1634 } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
1635 // If this instruction is IVIncrement then IV is new incoming value
1636 // from header otherwise this instruction must be incoming value from
1637 // header because loop is in LCSSA form.
1638 if (PHI == IVIncrement)
1639 PN->addIncoming(IV, Header);
1641 PN->addIncoming(V, Header);
1643 // Otherwise this is an incoming value from header because loop is in
1645 PN->addIncoming(V, Header);
1647 // Remove incoming value from Latch.
1648 PN->removeIncomingValue(Latch);