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 (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)))
689 if (!IndVarIncrement && PN == IndVar)
691 // else this is another loop induction variable
695 if ((PN = dyn_cast<PHINode>(Op1))) {
696 if ((CI = dyn_cast<ConstantInt>(Op0)))
698 if (!IndVarIncrement && PN == IndVar)
700 // else this is another loop induction variable
706 // I is an Exit condition if next instruction is block terminator.
707 // Exit condition is OK if it compares loop invariant exit value,
708 // which is checked below.
709 else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
710 if (EC == ExitCondition)
714 if (I == ExitingBlock->getTerminator())
717 // Otherwise we have instruction that may not be safe.
721 // We could not find any reason to consider ExitingBlock unsafe.
725 void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) {
727 Value *V0 = CI->getOperand(0);
728 Value *V1 = CI->getOperand(1);
731 SCEVHandle SH0 = SE->getSCEV(V0);
733 if (SH0->isLoopInvariant(L))
738 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
739 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
740 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
741 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
742 ExitCondition->swapOperands();
751 Value *UB = ExitCondition->getOperand(ExitValueNum);
752 const Type *Ty = NV->getType();
753 bool Sign = ExitCondition->isSignedPredicate();
754 BasicBlock *Preheader = L->getLoopPreheader();
755 Instruction *PHTerminator = Preheader->getTerminator();
757 assert (NV && "Unexpected value");
759 switch (CI->getPredicate()) {
760 case ICmpInst::ICMP_ULE:
761 case ICmpInst::ICMP_SLE:
762 // for (i = LB; i < UB; ++i)
763 // if (i <= NV && ...)
766 // is transformed into
767 // NUB = min (NV+1, UB)
768 // for (i = LB; i < NUB ; ++i)
771 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
772 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
773 Value *A = BinaryOperator::createAdd(NV, ConstantInt::get(Ty, 1, Sign),
774 "lsplit.add", PHTerminator);
775 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
776 A, UB,"lsplit,c", PHTerminator);
777 NUB = new SelectInst (C, A, UB, "lsplit.nub", PHTerminator);
780 // for (i = LB; i <= UB; ++i)
781 // if (i <= NV && ...)
784 // is transformed into
785 // NUB = min (NV, UB)
786 // for (i = LB; i <= NUB ; ++i)
789 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
790 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
791 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
792 NV, UB, "lsplit.c", PHTerminator);
793 NUB = new SelectInst (C, NV, UB, "lsplit.nub", PHTerminator);
796 case ICmpInst::ICMP_ULT:
797 case ICmpInst::ICMP_SLT:
798 // for (i = LB; i < UB; ++i)
799 // if (i < NV && ...)
802 // is transformed into
803 // NUB = min (NV, UB)
804 // for (i = LB; i < NUB ; ++i)
807 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
808 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
809 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
810 NV, UB, "lsplit.c", PHTerminator);
811 NUB = new SelectInst (C, NV, UB, "lsplit.nub", PHTerminator);
814 // for (i = LB; i <= UB; ++i)
815 // if (i < NV && ...)
818 // is transformed into
819 // NUB = min (NV -1 , UB)
820 // for (i = LB; i <= NUB ; ++i)
823 else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
824 || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
825 Value *S = BinaryOperator::createSub(NV, ConstantInt::get(Ty, 1, Sign),
826 "lsplit.add", PHTerminator);
827 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
828 S, UB, "lsplit.c", PHTerminator);
829 NUB = new SelectInst (C, S, UB, "lsplit.nub", PHTerminator);
832 case ICmpInst::ICMP_UGE:
833 case ICmpInst::ICMP_SGE:
834 // for (i = LB; i (< or <=) UB; ++i)
835 // if (i >= NV && ...)
838 // is transformed into
839 // NLB = max (NV, LB)
840 // for (i = NLB; i (< or <=) UB ; ++i)
844 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
845 NV, StartValue, "lsplit.c", PHTerminator);
846 NLB = new SelectInst (C, StartValue, NV, "lsplit.nlb", PHTerminator);
849 case ICmpInst::ICMP_UGT:
850 case ICmpInst::ICMP_SGT:
851 // for (i = LB; i (< or <=) UB; ++i)
852 // if (i > NV && ...)
855 // is transformed into
856 // NLB = max (NV+1, LB)
857 // for (i = NLB; i (< or <=) UB ; ++i)
861 Value *A = BinaryOperator::createAdd(NV, ConstantInt::get(Ty, 1, Sign),
862 "lsplit.add", PHTerminator);
863 Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
864 A, StartValue, "lsplit.c", PHTerminator);
865 NLB = new SelectInst (C, StartValue, A, "lsplit.nlb", PHTerminator);
869 assert ( 0 && "Unexpected split condition predicate");
873 unsigned i = IndVar->getBasicBlockIndex(Preheader);
874 IndVar->setIncomingValue(i, NLB);
878 ExitCondition->setOperand(ExitValueNum, NUB);
881 /// updateLoopIterationSpace - Current loop body is covered by an AND
882 /// instruction whose operands compares induction variables with loop
883 /// invariants. If possible, hoist this check outside the loop by
884 /// updating appropriate start and end values for induction variable.
885 bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) {
886 BasicBlock *Header = L->getHeader();
887 BasicBlock *ExitingBlock = ExitCondition->getParent();
888 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
890 ICmpInst *Op0 = cast<ICmpInst>(SD.SplitCondition->getOperand(0));
891 ICmpInst *Op1 = cast<ICmpInst>(SD.SplitCondition->getOperand(1));
893 if (Op0->getPredicate() == ICmpInst::ICMP_EQ
894 || Op0->getPredicate() == ICmpInst::ICMP_NE
895 || Op0->getPredicate() == ICmpInst::ICMP_EQ
896 || Op0->getPredicate() == ICmpInst::ICMP_NE)
899 // Check if SplitCondition dominates entire loop body
902 // If SplitCondition is not in loop header then this loop is not suitable
903 // for this transformation.
904 if (SD.SplitCondition->getParent() != Header)
907 // If loop header includes loop variant instruction operands then
908 // this loop may not be eliminated.
909 Instruction *Terminator = Header->getTerminator();
910 for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
918 // SplitCondition itself is OK.
919 if (I == SD.SplitCondition)
921 if (I == Op0 || I == Op1)
924 // Induction variable is OK.
928 // Induction variable increment is OK.
929 if (I == IndVarIncrement)
932 // Terminator is also harmless.
936 // Otherwise we have a instruction that may not be safe.
940 // If Exiting block includes loop variant instructions then this
941 // loop may not be eliminated.
942 if (!safeExitingBlock(SD, ExitCondition->getParent()))
945 // Verify that loop exiting block has only two predecessor, where one predecessor
946 // is split condition block. The other predecessor will become exiting block's
947 // dominator after CFG is updated. TODO : Handle CFG's where exiting block has
948 // more then two predecessors. This requires extra work in updating dominator
950 BasicBlock *ExitingBBPred = NULL;
951 for (pred_iterator PI = pred_begin(ExitingBlock), PE = pred_end(ExitingBlock);
953 BasicBlock *BB = *PI;
954 if (SplitCondBlock == BB)
962 // Update loop bounds to absorb Op0 check.
963 updateLoopBounds(Op0);
964 // Update loop bounds to absorb Op1 check.
965 updateLoopBounds(Op1);
969 // Unconditionally connect split block to its remaining successor.
970 BranchInst *SplitTerminator =
971 cast<BranchInst>(SplitCondBlock->getTerminator());
972 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
973 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
974 if (Succ0 == ExitCondition->getParent())
975 SplitTerminator->setUnconditionalDest(Succ1);
977 SplitTerminator->setUnconditionalDest(Succ0);
979 // Remove split condition.
980 SD.SplitCondition->eraseFromParent();
981 if (Op0->use_begin() == Op0->use_end())
982 Op0->eraseFromParent();
983 if (Op1->use_begin() == Op1->use_end())
984 Op1->eraseFromParent();
986 BranchInst *ExitInsn =
987 dyn_cast<BranchInst>(ExitingBlock->getTerminator());
988 assert (ExitInsn && "Unable to find suitable loop exit branch");
989 BasicBlock *ExitBlock = ExitInsn->getSuccessor(1);
990 if (L->contains(ExitBlock))
991 ExitBlock = ExitInsn->getSuccessor(0);
993 // Update domiantor info. Now, ExitingBlock has only one predecessor,
994 // ExitingBBPred, and it is ExitingBlock's immediate domiantor.
995 DT->changeImmediateDominator(ExitingBlock, ExitingBBPred);
997 // If ExitingBlock is a member of loop BB's DF list then replace it with
998 // loop header and exit block.
999 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
1001 BasicBlock *BB = *I;
1002 if (BB == Header || BB == ExitingBlock)
1004 DominanceFrontier::iterator BBDF = DF->find(BB);
1005 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1006 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1007 while (DomSetI != DomSetE) {
1008 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1010 BasicBlock *DFBB = *CurrentItr;
1011 if (DFBB == ExitingBlock) {
1012 BBDF->second.erase(DFBB);
1013 BBDF->second.insert(Header);
1014 if (Header != ExitingBlock)
1015 BBDF->second.insert(ExitBlock);
1024 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
1025 /// This routine is used to remove split condition's dead branch, dominated by
1026 /// DeadBB. LiveBB dominates split conidition's other branch.
1027 void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
1028 BasicBlock *LiveBB) {
1030 // First update DeadBB's dominance frontier.
1031 SmallVector<BasicBlock *, 8> FrontierBBs;
1032 DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
1033 if (DeadBBDF != DF->end()) {
1034 SmallVector<BasicBlock *, 8> PredBlocks;
1036 DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
1037 for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
1038 DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
1039 BasicBlock *FrontierBB = *DeadBBSetI;
1040 FrontierBBs.push_back(FrontierBB);
1042 // Rremove any PHI incoming edge from blocks dominated by DeadBB.
1044 for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
1046 BasicBlock *P = *PI;
1047 if (P == DeadBB || DT->dominates(DeadBB, P))
1048 PredBlocks.push_back(P);
1051 for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
1052 FBI != FBE; ++FBI) {
1053 if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
1054 for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
1055 PE = PredBlocks.end(); PI != PE; ++PI) {
1056 BasicBlock *P = *PI;
1057 PN->removeIncomingValue(P);
1066 // Now remove DeadBB and all nodes dominated by DeadBB in df order.
1067 SmallVector<BasicBlock *, 32> WorkList;
1068 DomTreeNode *DN = DT->getNode(DeadBB);
1069 for (df_iterator<DomTreeNode*> DI = df_begin(DN),
1070 E = df_end(DN); DI != E; ++DI) {
1071 BasicBlock *BB = DI->getBlock();
1072 WorkList.push_back(BB);
1073 BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
1076 while (!WorkList.empty()) {
1077 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
1078 for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
1080 Instruction *I = BBI;
1082 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1083 I->eraseFromParent();
1085 LPM->deleteSimpleAnalysisValue(BB, LP);
1087 DF->removeBlock(BB);
1088 LI->removeBlock(BB);
1089 BB->eraseFromParent();
1092 // Update Frontier BBs' dominator info.
1093 while (!FrontierBBs.empty()) {
1094 BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
1095 BasicBlock *NewDominator = FBB->getSinglePredecessor();
1096 if (!NewDominator) {
1097 pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
1100 if (NewDominator != LiveBB) {
1101 for(; PI != PE; ++PI) {
1102 BasicBlock *P = *PI;
1104 NewDominator = LiveBB;
1107 NewDominator = DT->findNearestCommonDominator(NewDominator, P);
1111 assert (NewDominator && "Unable to fix dominator info.");
1112 DT->changeImmediateDominator(FBB, NewDominator);
1113 DF->changeImmediateDominator(FBB, NewDominator, DT);
1118 /// safeSplitCondition - Return true if it is possible to
1119 /// split loop using given split condition.
1120 bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
1122 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1123 BasicBlock *Latch = L->getLoopLatch();
1124 BranchInst *SplitTerminator =
1125 cast<BranchInst>(SplitCondBlock->getTerminator());
1126 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1127 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1129 // Finally this split condition is safe only if merge point for
1130 // split condition branch is loop latch. This check along with previous
1131 // check, to ensure that exit condition is in either loop latch or header,
1132 // filters all loops with non-empty loop body between merge point
1133 // and exit condition.
1134 DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
1135 assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
1136 if (Succ0DF->second.count(Latch))
1139 DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
1140 assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
1141 if (Succ1DF->second.count(Latch))
1147 /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
1148 /// based on split value.
1149 void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
1151 ICmpInst *SC = cast<ICmpInst>(SD.SplitCondition);
1152 ICmpInst::Predicate SP = SC->getPredicate();
1153 const Type *Ty = SD.SplitValue->getType();
1154 bool Sign = ExitCondition->isSignedPredicate();
1155 BasicBlock *Preheader = L->getLoopPreheader();
1156 Instruction *PHTerminator = Preheader->getTerminator();
1158 // Initially use split value as upper loop bound for first loop and lower loop
1159 // bound for second loop.
1160 Value *AEV = SD.SplitValue;
1161 Value *BSV = SD.SplitValue;
1163 if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
1164 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
1165 || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
1166 || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE)
1167 ExitCondition->swapOperands();
1169 switch (ExitCondition->getPredicate()) {
1170 case ICmpInst::ICMP_SGT:
1171 case ICmpInst::ICMP_UGT:
1172 case ICmpInst::ICMP_SGE:
1173 case ICmpInst::ICMP_UGE:
1175 assert (0 && "Unexpected exit condition predicate");
1177 case ICmpInst::ICMP_SLT:
1178 case ICmpInst::ICMP_ULT:
1181 case ICmpInst::ICMP_SLT:
1182 case ICmpInst::ICMP_ULT:
1184 // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
1186 // is transformed into
1188 // for (i = LB; i < min(UB, AEV); ++i)
1190 // for (i = max(LB, BSV); i < UB; ++i);
1193 case ICmpInst::ICMP_SLE:
1194 case ICmpInst::ICMP_ULE:
1197 // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
1199 // is transformed into
1203 // for (i = LB; i < min(UB, AEV); ++i)
1205 // for (i = max(LB, BSV); i < UB; ++i)
1207 BSV = BinaryOperator::createAdd(SD.SplitValue,
1208 ConstantInt::get(Ty, 1, Sign),
1209 "lsplit.add", PHTerminator);
1213 case ICmpInst::ICMP_SGE:
1214 case ICmpInst::ICMP_UGE:
1216 // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
1218 // is transformed into
1220 // for (i = LB; i < min(UB, AEV); ++i)
1222 // for (i = max(BSV, LB); i < UB; ++i)
1225 case ICmpInst::ICMP_SGT:
1226 case ICmpInst::ICMP_UGT:
1229 // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
1231 // is transformed into
1233 // BSV = AEV = SV + 1
1234 // for (i = LB; i < min(UB, AEV); ++i)
1236 // for (i = max(LB, BSV); i < UB; ++i)
1238 BSV = BinaryOperator::createAdd(SD.SplitValue,
1239 ConstantInt::get(Ty, 1, Sign),
1240 "lsplit.add", PHTerminator);
1245 assert (0 && "Unexpected split condition predicate");
1247 } // end switch (SP)
1250 case ICmpInst::ICMP_SLE:
1251 case ICmpInst::ICMP_ULE:
1254 case ICmpInst::ICMP_SLT:
1255 case ICmpInst::ICMP_ULT:
1257 // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
1259 // is transformed into
1262 // for (i = LB; i <= min(UB, AEV); ++i)
1264 // for (i = max(LB, BSV); i <= UB; ++i)
1266 AEV = BinaryOperator::createSub(SD.SplitValue,
1267 ConstantInt::get(Ty, 1, Sign),
1268 "lsplit.sub", PHTerminator);
1270 case ICmpInst::ICMP_SLE:
1271 case ICmpInst::ICMP_ULE:
1273 // for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; }
1275 // is transformed into
1278 // for (i = LB; i <= min(UB, AEV); ++i)
1280 // for (i = max(LB, BSV); i <= UB; ++i)
1282 BSV = BinaryOperator::createAdd(SD.SplitValue,
1283 ConstantInt::get(Ty, 1, Sign),
1284 "lsplit.add", PHTerminator);
1286 case ICmpInst::ICMP_SGT:
1287 case ICmpInst::ICMP_UGT:
1289 // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
1291 // is transformed into
1294 // for (i = LB; i <= min(AEV, UB); ++i)
1296 // for (i = max(LB, BSV); i <= UB; ++i)
1298 BSV = BinaryOperator::createAdd(SD.SplitValue,
1299 ConstantInt::get(Ty, 1, Sign),
1300 "lsplit.add", PHTerminator);
1302 case ICmpInst::ICMP_SGE:
1303 case ICmpInst::ICMP_UGE:
1306 // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
1308 // is transformed into
1311 // for (i = LB; i <= min(AEV, UB); ++i)
1313 // for (i = max(LB, BSV); i <= UB; ++i)
1315 AEV = BinaryOperator::createSub(SD.SplitValue,
1316 ConstantInt::get(Ty, 1, Sign),
1317 "lsplit.sub", PHTerminator);
1320 assert (0 && "Unexpected split condition predicate");
1322 } // end switch (SP)
1327 // Calculate ALoop induction variable's new exiting value and
1328 // BLoop induction variable's new starting value. Calculuate these
1329 // values in original loop's preheader.
1330 // A_ExitValue = min(SplitValue, OrignalLoopExitValue)
1331 // B_StartValue = max(SplitValue, OriginalLoopStartValue)
1332 Instruction *InsertPt = L->getHeader()->getFirstNonPHI();
1333 Value *C1 = new ICmpInst(Sign ?
1334 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1336 ExitCondition->getOperand(ExitValueNum),
1337 "lsplit.ev", InsertPt);
1339 SD.A_ExitValue = new SelectInst(C1, AEV,
1340 ExitCondition->getOperand(ExitValueNum),
1341 "lsplit.ev", InsertPt);
1343 Value *C2 = new ICmpInst(Sign ?
1344 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
1345 BSV, StartValue, "lsplit.sv",
1347 SD.B_StartValue = new SelectInst(C2, StartValue, BSV,
1348 "lsplit.sv", PHTerminator);
1351 /// splitLoop - Split current loop L in two loops using split information
1352 /// SD. Update dominator information. Maintain LCSSA form.
1353 bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
1355 if (!safeSplitCondition(SD))
1358 BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
1360 // Unable to handle triange loops at the moment.
1361 // In triangle loop, split condition is in header and one of the
1362 // the split destination is loop latch. If split condition is EQ
1363 // then such loops are already handle in processOneIterationLoop().
1364 BasicBlock *Latch = L->getLoopLatch();
1365 BranchInst *SplitTerminator =
1366 cast<BranchInst>(SplitCondBlock->getTerminator());
1367 BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
1368 BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
1369 if (L->getHeader() == SplitCondBlock
1370 && (Latch == Succ0 || Latch == Succ1))
1373 // If split condition branches heads do not have single predecessor,
1374 // SplitCondBlock, then is not possible to remove inactive branch.
1375 if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor())
1378 // After loop is cloned there are two loops.
1380 // First loop, referred as ALoop, executes first part of loop's iteration
1381 // space split. Second loop, referred as BLoop, executes remaining
1382 // part of loop's iteration space.
1384 // ALoop's exit edge enters BLoop's header through a forwarding block which
1385 // acts as a BLoop's preheader.
1386 BasicBlock *Preheader = L->getLoopPreheader();
1388 // Calculate ALoop induction variable's new exiting value and
1389 // BLoop induction variable's new starting value.
1390 calculateLoopBounds(SD);
1393 DenseMap<const Value *, Value *> ValueMap;
1394 Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
1396 BasicBlock *B_Header = BLoop->getHeader();
1398 //[*] ALoop's exiting edge BLoop's header.
1399 // ALoop's original exit block becomes BLoop's exit block.
1400 PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
1401 BasicBlock *A_ExitingBlock = ExitCondition->getParent();
1402 BranchInst *A_ExitInsn =
1403 dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
1404 assert (A_ExitInsn && "Unable to find suitable loop exit branch");
1405 BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
1406 if (L->contains(B_ExitBlock)) {
1407 B_ExitBlock = A_ExitInsn->getSuccessor(0);
1408 A_ExitInsn->setSuccessor(0, B_Header);
1410 A_ExitInsn->setSuccessor(1, B_Header);
1412 //[*] Update ALoop's exit value using new exit value.
1413 ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
1415 // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
1416 // original loop's preheader. Add incoming PHINode values from
1417 // ALoop's exiting block. Update BLoop header's domiantor info.
1419 // Collect inverse map of Header PHINodes.
1420 DenseMap<Value *, Value *> InverseMap;
1421 for (BasicBlock::iterator BI = L->getHeader()->begin(),
1422 BE = L->getHeader()->end(); BI != BE; ++BI) {
1423 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1424 PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
1425 InverseMap[PNClone] = PN;
1430 for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1432 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1433 // Remove incoming value from original preheader.
1434 PN->removeIncomingValue(Preheader);
1436 // Add incoming value from A_ExitingBlock.
1438 PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
1440 PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
1441 Value *V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
1442 PN->addIncoming(V2, A_ExitingBlock);
1447 DT->changeImmediateDominator(B_Header, A_ExitingBlock);
1448 DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
1450 // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
1451 // block. Remove incoming PHINode values from ALoop's exiting block.
1452 // Add new incoming values from BLoop's incoming exiting value.
1453 // Update BLoop exit block's dominator info..
1454 BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
1455 for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
1457 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1458 PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
1460 PN->removeIncomingValue(A_ExitingBlock);
1465 DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
1466 DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
1468 //[*] Split ALoop's exit edge. This creates a new block which
1469 // serves two purposes. First one is to hold PHINode defnitions
1470 // to ensure that ALoop's LCSSA form. Second use it to act
1471 // as a preheader for BLoop.
1472 BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
1474 //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
1475 // in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
1476 for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1478 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1479 Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
1480 PHINode *newPHI = new PHINode(PN->getType(), PN->getName());
1481 newPHI->addIncoming(V1, A_ExitingBlock);
1482 A_ExitBlock->getInstList().push_front(newPHI);
1483 PN->removeIncomingValue(A_ExitBlock);
1484 PN->addIncoming(newPHI, A_ExitBlock);
1489 //[*] Eliminate split condition's inactive branch from ALoop.
1490 BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
1491 BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
1492 BasicBlock *A_InactiveBranch = NULL;
1493 BasicBlock *A_ActiveBranch = NULL;
1494 if (SD.UseTrueBranchFirst) {
1495 A_ActiveBranch = A_BR->getSuccessor(0);
1496 A_InactiveBranch = A_BR->getSuccessor(1);
1498 A_ActiveBranch = A_BR->getSuccessor(1);
1499 A_InactiveBranch = A_BR->getSuccessor(0);
1501 A_BR->setUnconditionalDest(A_ActiveBranch);
1502 removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
1504 //[*] Eliminate split condition's inactive branch in from BLoop.
1505 BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
1506 BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
1507 BasicBlock *B_InactiveBranch = NULL;
1508 BasicBlock *B_ActiveBranch = NULL;
1509 if (SD.UseTrueBranchFirst) {
1510 B_ActiveBranch = B_BR->getSuccessor(1);
1511 B_InactiveBranch = B_BR->getSuccessor(0);
1513 B_ActiveBranch = B_BR->getSuccessor(0);
1514 B_InactiveBranch = B_BR->getSuccessor(1);
1516 B_BR->setUnconditionalDest(B_ActiveBranch);
1517 removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
1519 BasicBlock *A_Header = L->getHeader();
1520 if (A_ExitingBlock == A_Header)
1523 //[*] Move exit condition into split condition block to avoid
1524 // executing dead loop iteration.
1525 ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
1526 Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
1527 ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
1529 moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
1530 cast<ICmpInst>(SD.SplitCondition), IndVar, IndVarIncrement,
1533 moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
1534 B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
1539 // moveExitCondition - Move exit condition EC into split condition block CondBB.
1540 void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
1541 BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
1542 PHINode *IV, Instruction *IVAdd, Loop *LP) {
1544 BasicBlock *ExitingBB = EC->getParent();
1545 Instruction *CurrentBR = CondBB->getTerminator();
1547 // Move exit condition into split condition block.
1548 EC->moveBefore(CurrentBR);
1549 EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
1551 // Move exiting block's branch into split condition block. Update its branch
1553 BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
1554 ExitingBR->moveBefore(CurrentBR);
1555 if (ExitingBR->getSuccessor(0) == ExitBB)
1556 ExitingBR->setSuccessor(1, ActiveBB);
1558 ExitingBR->setSuccessor(0, ActiveBB);
1560 // Remove split condition and current split condition branch.
1561 SC->eraseFromParent();
1562 CurrentBR->eraseFromParent();
1564 // Connect exiting block to split condition block.
1565 new BranchInst(CondBB, ExitingBB);
1568 updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd);
1570 // Fix dominator info.
1571 // ExitBB is now dominated by CondBB
1572 DT->changeImmediateDominator(ExitBB, CondBB);
1573 DF->changeImmediateDominator(ExitBB, CondBB, DT);
1575 // Basicblocks dominated by ActiveBB may have ExitingBB or
1576 // a basic block outside the loop in their DF list. If so,
1577 // replace it with CondBB.
1578 DomTreeNode *Node = DT->getNode(ActiveBB);
1579 for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
1581 BasicBlock *BB = DI->getBlock();
1582 DominanceFrontier::iterator BBDF = DF->find(BB);
1583 DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
1584 DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
1585 while (DomSetI != DomSetE) {
1586 DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
1588 BasicBlock *DFBB = *CurrentItr;
1589 if (DFBB == ExitingBB || !L->contains(DFBB)) {
1590 BBDF->second.erase(DFBB);
1591 BBDF->second.insert(CondBB);
1597 /// updatePHINodes - CFG has been changed.
1599 /// - ExitBB's single predecessor was Latch
1600 /// - Latch's second successor was Header
1602 /// - ExitBB's single predecessor was Header
1603 /// - Latch's one and only successor was Header
1605 /// Update ExitBB PHINodes' to reflect this change.
1606 void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
1608 PHINode *IV, Instruction *IVIncrement) {
1610 for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
1612 PHINode *PN = dyn_cast<PHINode>(BI);
1616 Value *V = PN->getIncomingValueForBlock(Latch);
1617 if (PHINode *PHV = dyn_cast<PHINode>(V)) {
1618 // PHV is in Latch. PHV has two uses, one use is in ExitBB PHINode
1620 // The second use is in Header and it is new incoming value for PN.
1624 for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
1627 U1 = cast<PHINode>(*UI);
1629 U2 = cast<PHINode>(*UI);
1631 assert ( 0 && "Unexpected third use of this PHINode");
1633 assert (U1 && U2 && "Unable to find two uses");
1635 if (U1->getParent() == Header)
1639 PN->addIncoming(NewV, Header);
1641 } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
1642 // If this instruction is IVIncrement then IV is new incoming value
1643 // from header otherwise this instruction must be incoming value from
1644 // header because loop is in LCSSA form.
1645 if (PHI == IVIncrement)
1646 PN->addIncoming(IV, Header);
1648 PN->addIncoming(V, Header);
1650 // Otherwise this is an incoming value from header because loop is in
1652 PN->addIncoming(V, Header);
1654 // Remove incoming value from Latch.
1655 PN->removeIncomingValue(Latch);