X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopIndexSplit.cpp;h=5faec97a9711d1b52fcc1f2016712b340599db38;hb=2a6a6457094e05e5f5ab34f90dbd25c13d61f8b5;hp=eb1a5b1c16bb6391f4a4f4f6fea6186b6ca4c610;hpb=6a2bfdaab62db8737bf54a8429da3cb8fbdfff62;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/LoopIndexSplit.cpp b/lib/Transforms/Scalar/LoopIndexSplit.cpp index eb1a5b1c16b..5faec97a971 100644 --- a/lib/Transforms/Scalar/LoopIndexSplit.cpp +++ b/lib/Transforms/Scalar/LoopIndexSplit.cpp @@ -2,8 +2,8 @@ // // The LLVM Compiler Infrastructure // -// This file was developed by Devang Patel and is distributed under -// the University of Illinois Open Source License. See LICENSE.TXT for details. +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // @@ -14,10 +14,13 @@ #define DEBUG_TYPE "loop-index-split" #include "llvm/Transforms/Scalar.h" -#include "llvm/Function.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/Analysis/Dominators.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Cloning.h" #include "llvm/Support/Compiler.h" +#include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/Statistic.h" using namespace llvm; @@ -40,131 +43,447 @@ namespace { AU.addPreserved(); AU.addRequiredID(LCSSAID); AU.addPreservedID(LCSSAID); + AU.addRequired(); AU.addPreserved(); AU.addRequiredID(LoopSimplifyID); AU.addPreservedID(LoopSimplifyID); + AU.addRequired(); + AU.addRequired(); + AU.addPreserved(); + AU.addPreserved(); } private: + + class SplitInfo { + public: + SplitInfo() : SplitValue(NULL), SplitCondition(NULL), + UseTrueBranchFirst(true), A_ExitValue(NULL), + B_StartValue(NULL) {} + + // Induction variable's range is split at this value. + Value *SplitValue; + + // This instruction compares IndVar against SplitValue. + Instruction *SplitCondition; + + // True if after loop index split, first loop will execute split condition's + // true branch. + bool UseTrueBranchFirst; + + // Exit value for first loop after loop split. + Value *A_ExitValue; + + // Start value for second loop after loop split. + Value *B_StartValue; + + // Clear split info. + void clear() { + SplitValue = NULL; + SplitCondition = NULL; + UseTrueBranchFirst = true; + A_ExitValue = NULL; + B_StartValue = NULL; + } + + }; + + private: + + // safeIcmpInst - CI is considered safe instruction if one of the operand + // is SCEVAddRecExpr based on induction variable and other operand is + // loop invariant. If CI is safe then populate SplitInfo object SD appropriately + // and return true; + bool safeICmpInst(ICmpInst *CI, SplitInfo &SD); + /// Find condition inside a loop that is suitable candidate for index split. void findSplitCondition(); + /// Find loop's exit condition. + void findLoopConditionals(); + + /// Return induction variable associated with value V. + void findIndVar(Value *V, Loop *L); + /// processOneIterationLoop - Current loop L contains compare instruction /// that compares induction variable, IndVar, agains loop invariant. If /// entire (i.e. meaningful) loop body is dominated by this compare /// instruction then loop body is executed only for one iteration. In /// such case eliminate loop structure surrounding this loop body. For - bool processOneIterationLoop(LPPassManager &LPM); - - // If loop header includes loop variant instruction operands then - // this loop may not be eliminated. - bool safeHeader(BasicBlock *BB); - - // If Exit block includes loop variant instructions then this - // loop may not be eliminated. - bool safeExitBlock(BasicBlock *BB); - - bool splitLoop(); + bool processOneIterationLoop(SplitInfo &SD); + + void updateLoopBounds(ICmpInst *CI); + /// updateLoopIterationSpace - Current loop body is covered by an AND + /// instruction whose operands compares induction variables with loop + /// invariants. If possible, hoist this check outside the loop by + /// updating appropriate start and end values for induction variable. + bool updateLoopIterationSpace(SplitInfo &SD); + + /// If loop header includes loop variant instruction operands then + /// this loop may not be eliminated. + bool safeHeader(SplitInfo &SD, BasicBlock *BB); + + /// If Exiting block includes loop variant instructions then this + /// loop may not be eliminated. + bool safeExitingBlock(SplitInfo &SD, BasicBlock *BB); + + /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB. + /// This routine is used to remove split condition's dead branch, dominated by + /// DeadBB. LiveBB dominates split conidition's other branch. + void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB); + + /// safeSplitCondition - Return true if it is possible to + /// split loop using given split condition. + bool safeSplitCondition(SplitInfo &SD); + + /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated + /// based on split value. + void calculateLoopBounds(SplitInfo &SD); + + /// updatePHINodes - CFG has been changed. + /// Before + /// - ExitBB's single predecessor was Latch + /// - Latch's second successor was Header + /// Now + /// - ExitBB's single predecessor was Header + /// - Latch's one and only successor was Header + /// + /// Update ExitBB PHINodes' to reflect this change. + void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch, + BasicBlock *Header, + PHINode *IV, Instruction *IVIncrement, Loop *LP); + + /// moveExitCondition - Move exit condition EC into split condition block CondBB. + void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB, + BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC, + PHINode *IV, Instruction *IVAdd, Loop *LP); + + /// splitLoop - Split current loop L in two loops using split information + /// SD. Update dominator information. Maintain LCSSA form. + bool splitLoop(SplitInfo &SD); + + void initialize() { + IndVar = NULL; + IndVarIncrement = NULL; + ExitCondition = NULL; + StartValue = NULL; + ExitValueNum = 0; + SplitData.clear(); + } private: // Current Loop. Loop *L; + LPPassManager *LPM; + LoopInfo *LI; ScalarEvolution *SE; + DominatorTree *DT; + DominanceFrontier *DF; + SmallVector SplitData; // Induction variable whose range is being split by this transformation. PHINode *IndVar; - - // Induction variable's range is split at this value. - Value *SplitValue; - - // Induction variable's final loop exit value. - Value *ExitValue; - - // This compare instruction compares IndVar against SplitValue. - ICmpInst *SplitCondition; - + Instruction *IndVarIncrement; + // Loop exit condition. ICmpInst *ExitCondition; - }; - char LoopIndexSplit::ID = 0; - RegisterPass X ("loop-index-split", "Index Split Loops"); + // Induction variable's initial value. + Value *StartValue; + + // Induction variable's final loop exit value operand number in exit condition.. + unsigned ExitValueNum; + }; } +char LoopIndexSplit::ID = 0; +static RegisterPass +X("loop-index-split", "Index Split Loops"); + LoopPass *llvm::createLoopIndexSplitPass() { return new LoopIndexSplit(); } // Index split Loop L. Return true if loop is split. -bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM) { +bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) { bool Changed = false; L = IncomingLoop; - SplitCondition = NULL; + LPM = &LPM_Ref; + + // FIXME - Nested loops make dominator info updates tricky. + if (!L->getSubLoops().empty()) + return false; + SE = &getAnalysis(); + DT = &getAnalysis(); + LI = &getAnalysis(); + DF = &getAnalysis(); + + initialize(); + + findLoopConditionals(); + + if (!ExitCondition) + return false; findSplitCondition(); - if (!SplitCondition) + if (SplitData.empty()) return false; - if (SplitCondition->getPredicate() == ICmpInst::ICMP_EQ) - // If it is possible to eliminate loop then do so. - Changed = processOneIterationLoop(LPM); - else - Changed = splitLoop(); + // First see if it is possible to eliminate loop itself or not. + for (SmallVector::iterator SI = SplitData.begin(); + SI != SplitData.end();) { + SplitInfo &SD = *SI; + ICmpInst *CI = dyn_cast(SD.SplitCondition); + if (SD.SplitCondition->getOpcode() == Instruction::And) { + Changed = updateLoopIterationSpace(SD); + if (Changed) { + ++NumIndexSplit; + // If is loop is eliminated then nothing else to do here. + return Changed; + } else { + SmallVector::iterator Delete_SI = SI; + SI = SplitData.erase(Delete_SI); + } + } + else if (CI && CI->getPredicate() == ICmpInst::ICMP_EQ) { + Changed = processOneIterationLoop(SD); + if (Changed) { + ++NumIndexSplit; + // If is loop is eliminated then nothing else to do here. + return Changed; + } else { + SmallVector::iterator Delete_SI = SI; + SI = SplitData.erase(Delete_SI); + } + } else + ++SI; + } + + if (SplitData.empty()) + return false; + + // Split most profitiable condition. + // FIXME : Implement cost analysis. + unsigned MostProfitableSDIndex = 0; + Changed = splitLoop(SplitData[MostProfitableSDIndex]); if (Changed) ++NumIndexSplit; - + return Changed; } -/// Find condition inside a loop that is suitable candidate for index split. -void LoopIndexSplit::findSplitCondition() { +/// Return true if V is a induction variable or induction variable's +/// increment for loop L. +void LoopIndexSplit::findIndVar(Value *V, Loop *L) { + + Instruction *I = dyn_cast(V); + if (!I) + return; + + // Check if I is a phi node from loop header or not. + if (PHINode *PN = dyn_cast(V)) { + if (PN->getParent() == L->getHeader()) { + IndVar = PN; + return; + } + } + + // Check if I is a add instruction whose one operand is + // phi node from loop header and second operand is constant. + if (I->getOpcode() != Instruction::Add) + return; + + Value *Op0 = I->getOperand(0); + Value *Op1 = I->getOperand(1); + + if (PHINode *PN = dyn_cast(Op0)) + if (PN->getParent() == L->getHeader()) + if (ConstantInt *CI = dyn_cast(Op1)) + if (CI->isOne()) { + IndVar = PN; + IndVarIncrement = I; + return; + } + + if (PHINode *PN = dyn_cast(Op1)) + if (PN->getParent() == L->getHeader()) + if (ConstantInt *CI = dyn_cast(Op0)) + if (CI->isOne()) { + IndVar = PN; + IndVarIncrement = I; + return; + } + + return; +} - BasicBlock *Header = L->getHeader(); +// Find loop's exit condition and associated induction variable. +void LoopIndexSplit::findLoopConditionals() { - for (BasicBlock::iterator I = Header->begin(); isa(I); ++I) { - PHINode *PN = cast(I); + BasicBlock *ExitingBlock = NULL; - if (!PN->getType()->isInteger()) + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); + I != E; ++I) { + BasicBlock *BB = *I; + if (!L->isLoopExit(BB)) continue; + if (ExitingBlock) + return; + ExitingBlock = BB; + } + + if (!ExitingBlock) + return; - SCEVHandle SCEV = SE->getSCEV(PN); - if (!isa(SCEV)) + // If exiting block is neither loop header nor loop latch then this loop is + // not suitable. + if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch()) + return; + + // If exit block's terminator is conditional branch inst then we have found + // exit condition. + BranchInst *BR = dyn_cast(ExitingBlock->getTerminator()); + if (!BR || BR->isUnconditional()) + return; + + ICmpInst *CI = dyn_cast(BR->getCondition()); + if (!CI) + return; + + // FIXME + if (CI->getPredicate() == ICmpInst::ICMP_EQ + || CI->getPredicate() == ICmpInst::ICMP_NE) + return; + + ExitCondition = CI; + + // Exit condition's one operand is loop invariant exit value and second + // operand is SCEVAddRecExpr based on induction variable. + Value *V0 = CI->getOperand(0); + Value *V1 = CI->getOperand(1); + + SCEVHandle SH0 = SE->getSCEV(V0); + SCEVHandle SH1 = SE->getSCEV(V1); + + if (SH0->isLoopInvariant(L) && isa(SH1)) { + ExitValueNum = 0; + findIndVar(V1, L); + } + else if (SH1->isLoopInvariant(L) && isa(SH0)) { + ExitValueNum = 1; + findIndVar(V0, L); + } + + if (!IndVar) + ExitCondition = NULL; + else if (IndVar) { + BasicBlock *Preheader = L->getLoopPreheader(); + StartValue = IndVar->getIncomingValueForBlock(Preheader); + } +} + +/// Find condition inside a loop that is suitable candidate for index split. +void LoopIndexSplit::findSplitCondition() { + + SplitInfo SD; + // Check all basic block's terminators. + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); + I != E; ++I) { + SD.clear(); + BasicBlock *BB = *I; + + // If this basic block does not terminate in a conditional branch + // then terminator is not a suitable split condition. + BranchInst *BR = dyn_cast(BB->getTerminator()); + if (!BR) + continue; + + if (BR->isUnconditional()) continue; - // If this phi node is used in a compare instruction then it is a - // split condition candidate. - for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); - UI != E; ++UI) { - if (ICmpInst *CI = dyn_cast(*UI)) { - SplitCondition = CI; - break; + if (Instruction *AndI = dyn_cast(BR->getCondition())) { + if (AndI->getOpcode() == Instruction::And) { + ICmpInst *Op0 = dyn_cast(AndI->getOperand(0)); + ICmpInst *Op1 = dyn_cast(AndI->getOperand(1)); + + if (!Op0 || !Op1) + continue; + + if (!safeICmpInst(Op0, SD)) + continue; + SD.clear(); + if (!safeICmpInst(Op1, SD)) + continue; + SD.clear(); + SD.SplitCondition = AndI; + SplitData.push_back(SD); + continue; } } + ICmpInst *CI = dyn_cast(BR->getCondition()); + if (!CI || CI == ExitCondition) + continue; - // Valid SplitCondition's one operand is phi node and the other operand - // is loop invariant. - if (SplitCondition) { - if (SplitCondition->getOperand(0) != PN) - SplitValue = SplitCondition->getOperand(0); - else - SplitValue = SplitCondition->getOperand(1); - SCEVHandle ValueSCEV = SE->getSCEV(SplitValue); + if (CI->getPredicate() == ICmpInst::ICMP_NE) + continue; - // If SplitValue is not invariant then SplitCondition is not appropriate. - if (!ValueSCEV->isLoopInvariant(L)) - SplitCondition = NULL; - } + // If split condition predicate is GT or GE then first execute + // false branch of split condition. + if (CI->getPredicate() == ICmpInst::ICMP_UGT + || CI->getPredicate() == ICmpInst::ICMP_SGT + || CI->getPredicate() == ICmpInst::ICMP_UGE + || CI->getPredicate() == ICmpInst::ICMP_SGE) + SD.UseTrueBranchFirst = false; + + // If one operand is loop invariant and second operand is SCEVAddRecExpr + // based on induction variable then CI is a candidate split condition. + if (safeICmpInst(CI, SD)) + SplitData.push_back(SD); + } +} - // We are looking for only one split condition. - if (SplitCondition) { - IndVar = PN; - break; +// safeIcmpInst - CI is considered safe instruction if one of the operand +// is SCEVAddRecExpr based on induction variable and other operand is +// loop invariant. If CI is safe then populate SplitInfo object SD appropriately +// and return true; +bool LoopIndexSplit::safeICmpInst(ICmpInst *CI, SplitInfo &SD) { + + Value *V0 = CI->getOperand(0); + Value *V1 = CI->getOperand(1); + + SCEVHandle SH0 = SE->getSCEV(V0); + SCEVHandle SH1 = SE->getSCEV(V1); + + if (SH0->isLoopInvariant(L) && isa(SH1)) { + SD.SplitValue = V0; + SD.SplitCondition = CI; + if (PHINode *PN = dyn_cast(V1)) { + if (PN == IndVar) + return true; + } + else if (Instruction *Insn = dyn_cast(V1)) { + if (IndVarIncrement && IndVarIncrement == Insn) + return true; + } + } + else if (SH1->isLoopInvariant(L) && isa(SH0)) { + SD.SplitValue = V1; + SD.SplitCondition = CI; + if (PHINode *PN = dyn_cast(V0)) { + if (PN == IndVar) + return true; + } + else if (Instruction *Insn = dyn_cast(V0)) { + if (IndVarIncrement && IndVarIncrement == Insn) + return true; } } + + return false; } /// processOneIterationLoop - Current loop L contains compare instruction @@ -182,7 +501,7 @@ void LoopIndexSplit::findSplitCondition() { /// i = somevalue; /// loop_body /// } -bool LoopIndexSplit::processOneIterationLoop(LPPassManager &LPM) { +bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) { BasicBlock *Header = L->getHeader(); @@ -191,40 +510,50 @@ bool LoopIndexSplit::processOneIterationLoop(LPPassManager &LPM) { // If SplitCondition is not in loop header then this loop is not suitable // for this transformation. - if (SplitCondition->getParent() != Header) + if (SD.SplitCondition->getParent() != Header) return false; - // If one of the Header block's successor is not an exit block then this - // loop is not a suitable candidate. - BasicBlock *ExitBlock = NULL; - for (succ_iterator SI = succ_begin(Header), E = succ_end(Header); SI != E; ++SI) { - if (L->isLoopExit(*SI)) { - ExitBlock = *SI; - break; - } - } - - if (!ExitBlock) - return false; - // If loop header includes loop variant instruction operands then // this loop may not be eliminated. - if (!safeHeader(Header)) + if (!safeHeader(SD, Header)) return false; - // If Exit block includes loop variant instructions then this + // If Exiting block includes loop variant instructions then this // loop may not be eliminated. - if (!safeExitBlock(ExitBlock)) + if (!safeExitingBlock(SD, ExitCondition->getParent())) return false; - // Update CFG. + // Filter loops where split condition's false branch is not empty. + if (ExitCondition->getParent() != Header->getTerminator()->getSuccessor(1)) + return false; + + // If split condition is not safe then do not process this loop. + // For example, + // for(int i = 0; i < N; i++) { + // if ( i == XYZ) { + // A; + // else + // B; + // } + // C; + // D; + // } + if (!safeSplitCondition(SD)) + return false; - // As a first step to break this loop, remove Latch to Header edge. BasicBlock *Latch = L->getLoopLatch(); - BasicBlock *LatchSucc = NULL; BranchInst *BR = dyn_cast(Latch->getTerminator()); if (!BR) return false; + + // Update CFG. + + // Replace index variable with split value in loop body. Loop body is executed + // only when index variable is equal to split value. + IndVar->replaceAllUsesWith(SD.SplitValue); + + // Remove Latch to Header edge. + BasicBlock *LatchSucc = NULL; Header->removePredecessor(Latch); for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch); SI != E; ++SI) { @@ -233,27 +562,29 @@ bool LoopIndexSplit::processOneIterationLoop(LPPassManager &LPM) { } BR->setUnconditionalDest(LatchSucc); - BasicBlock *Preheader = L->getLoopPreheader(); Instruction *Terminator = Header->getTerminator(); - Value *StartValue = IndVar->getIncomingValueForBlock(Preheader); + Value *ExitValue = ExitCondition->getOperand(ExitValueNum); // Replace split condition in header. // Transform // SplitCondition : icmp eq i32 IndVar, SplitValue // into // c1 = icmp uge i32 SplitValue, StartValue - // c2 = icmp ult i32 vSplitValue, ExitValue + // c2 = icmp ult i32 SplitValue, ExitValue // and i32 c1, c2 bool SignedPredicate = ExitCondition->isSignedPredicate(); Instruction *C1 = new ICmpInst(SignedPredicate ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE, - SplitValue, StartValue, "lisplit", Terminator); + SD.SplitValue, StartValue, "lisplit", + Terminator); Instruction *C2 = new ICmpInst(SignedPredicate ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, - SplitValue, ExitValue, "lisplit", Terminator); - Instruction *NSplitCond = BinaryOperator::createAnd(C1, C2, "lisplit", Terminator); - SplitCondition->replaceAllUsesWith(NSplitCond); - SplitCondition->eraseFromParent(); + SD.SplitValue, ExitValue, "lisplit", + Terminator); + Instruction *NSplitCond = BinaryOperator::CreateAnd(C1, C2, "lisplit", + Terminator); + SD.SplitCondition->replaceAllUsesWith(NSplitCond); + SD.SplitCondition->eraseFromParent(); // Now, clear latch block. Remove instructions that are responsible // to increment induction variable. @@ -265,29 +596,70 @@ bool LoopIndexSplit::processOneIterationLoop(LPPassManager &LPM) { if (isa(I) || I == LTerminator) continue; - I->replaceAllUsesWith(UndefValue::get(I->getType())); - I->eraseFromParent(); + if (I == IndVarIncrement) { + // Replace induction variable increment if it is not used outside + // the loop. + bool UsedOutsideLoop = false; + for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); + UI != E; ++UI) { + if (Instruction *Use = dyn_cast(UI)) + if (!L->contains(Use->getParent())) { + UsedOutsideLoop = true; + break; + } + } + if (!UsedOutsideLoop) { + I->replaceAllUsesWith(ExitValue); + I->eraseFromParent(); + } + } + else { + I->replaceAllUsesWith(UndefValue::get(I->getType())); + I->eraseFromParent(); + } } - LPM.deleteLoopFromQueue(L); + LPM->deleteLoopFromQueue(L); + + // Update Dominator Info. + // Only CFG change done is to remove Latch to Header edge. This + // does not change dominator tree because Latch did not dominate + // Header. + if (DF) { + DominanceFrontier::iterator HeaderDF = DF->find(Header); + if (HeaderDF != DF->end()) + DF->removeFromFrontier(HeaderDF, Header); + + DominanceFrontier::iterator LatchDF = DF->find(Latch); + if (LatchDF != DF->end()) + DF->removeFromFrontier(LatchDF, Header); + } return true; } // If loop header includes loop variant instruction operands then // this loop can not be eliminated. This is used by processOneIterationLoop(). -bool LoopIndexSplit::safeHeader(BasicBlock *Header) { +bool LoopIndexSplit::safeHeader(SplitInfo &SD, BasicBlock *Header) { Instruction *Terminator = Header->getTerminator(); for(BasicBlock::iterator BI = Header->begin(), BE = Header->end(); BI != BE; ++BI) { Instruction *I = BI; - // PHI Nodes are OK. FIXME : Handle last value assignments. + // PHI Nodes are OK. if (isa(I)) continue; // SplitCondition itself is OK. - if (I == SplitCondition) + if (I == SD.SplitCondition) + continue; + + // Induction variable is OK. + if (I == IndVar) + continue; + + // Induction variable increment is OK. + if (I == IndVarIncrement) continue; // Terminator is also harmless. @@ -301,84 +673,1037 @@ bool LoopIndexSplit::safeHeader(BasicBlock *Header) { return true; } -// If Exit block includes loop variant instructions then this +// If Exiting block includes loop variant instructions then this // loop may not be eliminated. This is used by processOneIterationLoop(). -bool LoopIndexSplit::safeExitBlock(BasicBlock *ExitBlock) { +bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD, + BasicBlock *ExitingBlock) { - Instruction *IndVarIncrement = NULL; - - for (BasicBlock::iterator BI = ExitBlock->begin(), BE = ExitBlock->end(); - BI != BE; ++BI) { + for (BasicBlock::iterator BI = ExitingBlock->begin(), + BE = ExitingBlock->end(); BI != BE; ++BI) { Instruction *I = BI; - // PHI Nodes are OK. FIXME : Handle last value assignments. + // PHI Nodes are OK. if (isa(I)) continue; + // Induction variable increment is OK. + if (IndVarIncrement && IndVarIncrement == I) + continue; + // Check if I is induction variable increment instruction. - if (BinaryOperator *BOp = dyn_cast(I)) { - if (BOp->getOpcode() != Instruction::Add) - return false; + if (I->getOpcode() == Instruction::Add) { - Value *Op0 = BOp->getOperand(0); - Value *Op1 = BOp->getOperand(1); + Value *Op0 = I->getOperand(0); + Value *Op1 = I->getOperand(1); PHINode *PN = NULL; ConstantInt *CI = NULL; if ((PN = dyn_cast(Op0))) { if ((CI = dyn_cast(Op1))) - IndVarIncrement = I; + if (CI->isOne()) { + if (!IndVarIncrement && PN == IndVar) + IndVarIncrement = I; + // else this is another loop induction variable + continue; + } } else if ((PN = dyn_cast(Op1))) { if ((CI = dyn_cast(Op0))) - IndVarIncrement = I; + if (CI->isOne()) { + if (!IndVarIncrement && PN == IndVar) + IndVarIncrement = I; + // else this is another loop induction variable + continue; + } } - - if (IndVarIncrement && PN == IndVar && CI->isOne()) - continue; - } + } // I is an Exit condition if next instruction is block terminator. // Exit condition is OK if it compares loop invariant exit value, // which is checked below. else if (ICmpInst *EC = dyn_cast(I)) { - ++BI; - Instruction *N = BI; - if (N == ExitBlock->getTerminator()) { - ExitCondition = EC; + if (EC == ExitCondition) continue; - } } + if (I == ExitingBlock->getTerminator()) + continue; + // Otherwise we have instruction that may not be safe. return false; } - // Check if Exit condition is comparing induction variable against - // loop invariant value. If one operand is induction variable and - // the other operand is loop invaraint then Exit condition is safe. - if (ExitCondition) { - Value *Op0 = ExitCondition->getOperand(0); - Value *Op1 = ExitCondition->getOperand(1); + // We could not find any reason to consider ExitingBlock unsafe. + return true; +} - Instruction *Insn0 = dyn_cast(Op0); - Instruction *Insn1 = dyn_cast(Op1); +void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) { + + Value *V0 = CI->getOperand(0); + Value *V1 = CI->getOperand(1); + Value *NV = NULL; + + SCEVHandle SH0 = SE->getSCEV(V0); + + if (SH0->isLoopInvariant(L)) + NV = V0; + else + NV = V1; + + if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT + || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT + || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE + || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) { + ExitCondition->swapOperands(); + if (ExitValueNum) + ExitValueNum = 0; + else + ExitValueNum = 1; + } + + Value *NUB = NULL; + Value *NLB = NULL; + Value *UB = ExitCondition->getOperand(ExitValueNum); + const Type *Ty = NV->getType(); + bool Sign = ExitCondition->isSignedPredicate(); + BasicBlock *Preheader = L->getLoopPreheader(); + Instruction *PHTerminator = Preheader->getTerminator(); + + assert (NV && "Unexpected value"); + + switch (CI->getPredicate()) { + case ICmpInst::ICMP_ULE: + case ICmpInst::ICMP_SLE: + // for (i = LB; i < UB; ++i) + // if (i <= NV && ...) + // LOOP_BODY + // + // is transformed into + // NUB = min (NV+1, UB) + // for (i = LB; i < NUB ; ++i) + // LOOP_BODY + // + if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT + || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) { + Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign), + "lsplit.add", PHTerminator); + Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + A, UB,"lsplit,c", PHTerminator); + NUB = SelectInst::Create(C, A, UB, "lsplit.nub", PHTerminator); + } - if (Insn0 && Insn0 == IndVarIncrement) - ExitValue = Op1; - else if (Insn1 && Insn1 == IndVarIncrement) - ExitValue = Op0; + // for (i = LB; i <= UB; ++i) + // if (i <= NV && ...) + // LOOP_BODY + // + // is transformed into + // NUB = min (NV, UB) + // for (i = LB; i <= NUB ; ++i) + // LOOP_BODY + // + else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE + || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) { + Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + NV, UB, "lsplit.c", PHTerminator); + NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator); + } + break; + case ICmpInst::ICMP_ULT: + case ICmpInst::ICMP_SLT: + // for (i = LB; i < UB; ++i) + // if (i < NV && ...) + // LOOP_BODY + // + // is transformed into + // NUB = min (NV, UB) + // for (i = LB; i < NUB ; ++i) + // LOOP_BODY + // + if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT + || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) { + Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + NV, UB, "lsplit.c", PHTerminator); + NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator); + } - SCEVHandle ValueSCEV = SE->getSCEV(ExitValue); - if (!ValueSCEV->isLoopInvariant(L)) + // for (i = LB; i <= UB; ++i) + // if (i < NV && ...) + // LOOP_BODY + // + // is transformed into + // NUB = min (NV -1 , UB) + // for (i = LB; i <= NUB ; ++i) + // LOOP_BODY + // + else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE + || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) { + Value *S = BinaryOperator::CreateSub(NV, ConstantInt::get(Ty, 1, Sign), + "lsplit.add", PHTerminator); + Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + S, UB, "lsplit.c", PHTerminator); + NUB = SelectInst::Create(C, S, UB, "lsplit.nub", PHTerminator); + } + break; + case ICmpInst::ICMP_UGE: + case ICmpInst::ICMP_SGE: + // for (i = LB; i (< or <=) UB; ++i) + // if (i >= NV && ...) + // LOOP_BODY + // + // is transformed into + // NLB = max (NV, LB) + // for (i = NLB; i (< or <=) UB ; ++i) + // LOOP_BODY + // + { + Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + NV, StartValue, "lsplit.c", PHTerminator); + NLB = SelectInst::Create(C, StartValue, NV, "lsplit.nlb", PHTerminator); + } + break; + case ICmpInst::ICMP_UGT: + case ICmpInst::ICMP_SGT: + // for (i = LB; i (< or <=) UB; ++i) + // if (i > NV && ...) + // LOOP_BODY + // + // is transformed into + // NLB = max (NV+1, LB) + // for (i = NLB; i (< or <=) UB ; ++i) + // LOOP_BODY + // + { + Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign), + "lsplit.add", PHTerminator); + Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + A, StartValue, "lsplit.c", PHTerminator); + NLB = SelectInst::Create(C, StartValue, A, "lsplit.nlb", PHTerminator); + } + break; + default: + assert ( 0 && "Unexpected split condition predicate"); + } + + if (NLB) { + unsigned i = IndVar->getBasicBlockIndex(Preheader); + IndVar->setIncomingValue(i, NLB); + } + + if (NUB) { + ExitCondition->setOperand(ExitValueNum, NUB); + } +} +/// updateLoopIterationSpace - Current loop body is covered by an AND +/// instruction whose operands compares induction variables with loop +/// invariants. If possible, hoist this check outside the loop by +/// updating appropriate start and end values for induction variable. +bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) { + BasicBlock *Header = L->getHeader(); + BasicBlock *ExitingBlock = ExitCondition->getParent(); + BasicBlock *SplitCondBlock = SD.SplitCondition->getParent(); + + ICmpInst *Op0 = cast(SD.SplitCondition->getOperand(0)); + ICmpInst *Op1 = cast(SD.SplitCondition->getOperand(1)); + + if (Op0->getPredicate() == ICmpInst::ICMP_EQ + || Op0->getPredicate() == ICmpInst::ICMP_NE + || Op0->getPredicate() == ICmpInst::ICMP_EQ + || Op0->getPredicate() == ICmpInst::ICMP_NE) + return false; + + // Check if SplitCondition dominates entire loop body + // or not. + + // If SplitCondition is not in loop header then this loop is not suitable + // for this transformation. + if (SD.SplitCondition->getParent() != Header) + return false; + + // If loop header includes loop variant instruction operands then + // this loop may not be eliminated. + Instruction *Terminator = Header->getTerminator(); + for(BasicBlock::iterator BI = Header->begin(), BE = Header->end(); + BI != BE; ++BI) { + Instruction *I = BI; + + // PHI Nodes are OK. + if (isa(I)) + continue; + + // SplitCondition itself is OK. + if (I == SD.SplitCondition) + continue; + if (I == Op0 || I == Op1) + continue; + + // Induction variable is OK. + if (I == IndVar) + continue; + + // Induction variable increment is OK. + if (I == IndVarIncrement) + continue; + + // Terminator is also harmless. + if (I == Terminator) + continue; + + // Otherwise we have a instruction that may not be safe. + return false; + } + + // If Exiting block includes loop variant instructions then this + // loop may not be eliminated. + if (!safeExitingBlock(SD, ExitCondition->getParent())) + return false; + + // Verify that loop exiting block has only two predecessor, where one predecessor + // is split condition block. The other predecessor will become exiting block's + // dominator after CFG is updated. TODO : Handle CFG's where exiting block has + // more then two predecessors. This requires extra work in updating dominator + // information. + BasicBlock *ExitingBBPred = NULL; + for (pred_iterator PI = pred_begin(ExitingBlock), PE = pred_end(ExitingBlock); + PI != PE; ++PI) { + BasicBlock *BB = *PI; + if (SplitCondBlock == BB) + continue; + if (ExitingBBPred) return false; + else + ExitingBBPred = BB; + } + + // Update loop bounds to absorb Op0 check. + updateLoopBounds(Op0); + // Update loop bounds to absorb Op1 check. + updateLoopBounds(Op1); + + // Update CFG + + // Unconditionally connect split block to its remaining successor. + BranchInst *SplitTerminator = + cast(SplitCondBlock->getTerminator()); + BasicBlock *Succ0 = SplitTerminator->getSuccessor(0); + BasicBlock *Succ1 = SplitTerminator->getSuccessor(1); + if (Succ0 == ExitCondition->getParent()) + SplitTerminator->setUnconditionalDest(Succ1); + else + SplitTerminator->setUnconditionalDest(Succ0); + + // Remove split condition. + SD.SplitCondition->eraseFromParent(); + if (Op0->use_begin() == Op0->use_end()) + Op0->eraseFromParent(); + if (Op1->use_begin() == Op1->use_end()) + Op1->eraseFromParent(); + + BranchInst *ExitInsn = + dyn_cast(ExitingBlock->getTerminator()); + assert (ExitInsn && "Unable to find suitable loop exit branch"); + BasicBlock *ExitBlock = ExitInsn->getSuccessor(1); + if (L->contains(ExitBlock)) + ExitBlock = ExitInsn->getSuccessor(0); + + // Update domiantor info. Now, ExitingBlock has only one predecessor, + // ExitingBBPred, and it is ExitingBlock's immediate domiantor. + DT->changeImmediateDominator(ExitingBlock, ExitingBBPred); + + // If ExitingBlock is a member of loop BB's DF list then replace it with + // loop header and exit block. + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); + I != E; ++I) { + BasicBlock *BB = *I; + if (BB == Header || BB == ExitingBlock) + continue; + DominanceFrontier::iterator BBDF = DF->find(BB); + DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin(); + DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end(); + while (DomSetI != DomSetE) { + DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI; + ++DomSetI; + BasicBlock *DFBB = *CurrentItr; + if (DFBB == ExitingBlock) { + BBDF->second.erase(DFBB); + BBDF->second.insert(Header); + if (Header != ExitingBlock) + BBDF->second.insert(ExitBlock); + } + } } - // We could not find any reason to consider ExitBlock unsafe. return true; } -bool LoopIndexSplit::splitLoop() { - // FIXME :) + +/// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB. +/// This routine is used to remove split condition's dead branch, dominated by +/// DeadBB. LiveBB dominates split conidition's other branch. +void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP, + BasicBlock *LiveBB) { + + // First update DeadBB's dominance frontier. + SmallVector FrontierBBs; + DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB); + if (DeadBBDF != DF->end()) { + SmallVector PredBlocks; + + DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second; + for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(), + DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) { + BasicBlock *FrontierBB = *DeadBBSetI; + FrontierBBs.push_back(FrontierBB); + + // Rremove any PHI incoming edge from blocks dominated by DeadBB. + PredBlocks.clear(); + for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB); + PI != PE; ++PI) { + BasicBlock *P = *PI; + if (P == DeadBB || DT->dominates(DeadBB, P)) + PredBlocks.push_back(P); + } + + for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end(); + FBI != FBE; ++FBI) { + if (PHINode *PN = dyn_cast(FBI)) { + for(SmallVector::iterator PI = PredBlocks.begin(), + PE = PredBlocks.end(); PI != PE; ++PI) { + BasicBlock *P = *PI; + PN->removeIncomingValue(P); + } + } + else + break; + } + } + } + + // Now remove DeadBB and all nodes dominated by DeadBB in df order. + SmallVector WorkList; + DomTreeNode *DN = DT->getNode(DeadBB); + for (df_iterator DI = df_begin(DN), + E = df_end(DN); DI != E; ++DI) { + BasicBlock *BB = DI->getBlock(); + WorkList.push_back(BB); + BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy)); + } + + while (!WorkList.empty()) { + BasicBlock *BB = WorkList.back(); WorkList.pop_back(); + for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end(); + BBI != BBE; ) { + Instruction *I = BBI; + ++BBI; + I->replaceAllUsesWith(UndefValue::get(I->getType())); + I->eraseFromParent(); + } + LPM->deleteSimpleAnalysisValue(BB, LP); + DT->eraseNode(BB); + DF->removeBlock(BB); + LI->removeBlock(BB); + BB->eraseFromParent(); + } + + // Update Frontier BBs' dominator info. + while (!FrontierBBs.empty()) { + BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back(); + BasicBlock *NewDominator = FBB->getSinglePredecessor(); + if (!NewDominator) { + pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB); + NewDominator = *PI; + ++PI; + if (NewDominator != LiveBB) { + for(; PI != PE; ++PI) { + BasicBlock *P = *PI; + if (P == LiveBB) { + NewDominator = LiveBB; + break; + } + NewDominator = DT->findNearestCommonDominator(NewDominator, P); + } + } + } + assert (NewDominator && "Unable to fix dominator info."); + DT->changeImmediateDominator(FBB, NewDominator); + DF->changeImmediateDominator(FBB, NewDominator, DT); + } + +} + +/// safeSplitCondition - Return true if it is possible to +/// split loop using given split condition. +bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) { + + BasicBlock *SplitCondBlock = SD.SplitCondition->getParent(); + BasicBlock *Latch = L->getLoopLatch(); + BranchInst *SplitTerminator = + cast(SplitCondBlock->getTerminator()); + BasicBlock *Succ0 = SplitTerminator->getSuccessor(0); + BasicBlock *Succ1 = SplitTerminator->getSuccessor(1); + + // If split block does not dominate the latch then this is not a diamond. + // Such loop may not benefit from index split. + if (!DT->dominates(SplitCondBlock, Latch)) + return false; + + // Finally this split condition is safe only if merge point for + // split condition branch is loop latch. This check along with previous + // check, to ensure that exit condition is in either loop latch or header, + // filters all loops with non-empty loop body between merge point + // and exit condition. + DominanceFrontier::iterator Succ0DF = DF->find(Succ0); + assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier"); + if (Succ0DF->second.count(Latch)) + return true; + + DominanceFrontier::iterator Succ1DF = DF->find(Succ1); + assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier"); + if (Succ1DF->second.count(Latch)) + return true; + return false; } + +/// calculateLoopBounds - ALoop exit value and BLoop start values are calculated +/// based on split value. +void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) { + + ICmpInst *SC = cast(SD.SplitCondition); + ICmpInst::Predicate SP = SC->getPredicate(); + const Type *Ty = SD.SplitValue->getType(); + bool Sign = ExitCondition->isSignedPredicate(); + BasicBlock *Preheader = L->getLoopPreheader(); + Instruction *PHTerminator = Preheader->getTerminator(); + + // Initially use split value as upper loop bound for first loop and lower loop + // bound for second loop. + Value *AEV = SD.SplitValue; + Value *BSV = SD.SplitValue; + + if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT + || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT + || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE + || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) { + ExitCondition->swapOperands(); + if (ExitValueNum) + ExitValueNum = 0; + else + ExitValueNum = 1; + } + + switch (ExitCondition->getPredicate()) { + case ICmpInst::ICMP_SGT: + case ICmpInst::ICMP_UGT: + case ICmpInst::ICMP_SGE: + case ICmpInst::ICMP_UGE: + default: + assert (0 && "Unexpected exit condition predicate"); + + case ICmpInst::ICMP_SLT: + case ICmpInst::ICMP_ULT: + { + switch (SP) { + case ICmpInst::ICMP_SLT: + case ICmpInst::ICMP_ULT: + // + // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; } + // + // is transformed into + // AEV = BSV = SV + // for (i = LB; i < min(UB, AEV); ++i) + // A; + // for (i = max(LB, BSV); i < UB; ++i); + // B; + break; + case ICmpInst::ICMP_SLE: + case ICmpInst::ICMP_ULE: + { + // + // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; } + // + // is transformed into + // + // AEV = SV + 1 + // BSV = SV + 1 + // for (i = LB; i < min(UB, AEV); ++i) + // A; + // for (i = max(LB, BSV); i < UB; ++i) + // B; + BSV = BinaryOperator::CreateAdd(SD.SplitValue, + ConstantInt::get(Ty, 1, Sign), + "lsplit.add", PHTerminator); + AEV = BSV; + } + break; + case ICmpInst::ICMP_SGE: + case ICmpInst::ICMP_UGE: + // + // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; } + // + // is transformed into + // AEV = BSV = SV + // for (i = LB; i < min(UB, AEV); ++i) + // B; + // for (i = max(BSV, LB); i < UB; ++i) + // A; + break; + case ICmpInst::ICMP_SGT: + case ICmpInst::ICMP_UGT: + { + // + // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; } + // + // is transformed into + // + // BSV = AEV = SV + 1 + // for (i = LB; i < min(UB, AEV); ++i) + // B; + // for (i = max(LB, BSV); i < UB; ++i) + // A; + BSV = BinaryOperator::CreateAdd(SD.SplitValue, + ConstantInt::get(Ty, 1, Sign), + "lsplit.add", PHTerminator); + AEV = BSV; + } + break; + default: + assert (0 && "Unexpected split condition predicate"); + break; + } // end switch (SP) + } + break; + case ICmpInst::ICMP_SLE: + case ICmpInst::ICMP_ULE: + { + switch (SP) { + case ICmpInst::ICMP_SLT: + case ICmpInst::ICMP_ULT: + // + // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; } + // + // is transformed into + // AEV = SV - 1; + // BSV = SV; + // for (i = LB; i <= min(UB, AEV); ++i) + // A; + // for (i = max(LB, BSV); i <= UB; ++i) + // B; + AEV = BinaryOperator::CreateSub(SD.SplitValue, + ConstantInt::get(Ty, 1, Sign), + "lsplit.sub", PHTerminator); + break; + case ICmpInst::ICMP_SLE: + case ICmpInst::ICMP_ULE: + // + // for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; } + // + // is transformed into + // AEV = SV; + // BSV = SV + 1; + // for (i = LB; i <= min(UB, AEV); ++i) + // A; + // for (i = max(LB, BSV); i <= UB; ++i) + // B; + BSV = BinaryOperator::CreateAdd(SD.SplitValue, + ConstantInt::get(Ty, 1, Sign), + "lsplit.add", PHTerminator); + break; + case ICmpInst::ICMP_SGT: + case ICmpInst::ICMP_UGT: + // + // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; } + // + // is transformed into + // AEV = SV; + // BSV = SV + 1; + // for (i = LB; i <= min(AEV, UB); ++i) + // B; + // for (i = max(LB, BSV); i <= UB; ++i) + // A; + BSV = BinaryOperator::CreateAdd(SD.SplitValue, + ConstantInt::get(Ty, 1, Sign), + "lsplit.add", PHTerminator); + break; + case ICmpInst::ICMP_SGE: + case ICmpInst::ICMP_UGE: + // ** TODO ** + // + // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; } + // + // is transformed into + // AEV = SV - 1; + // BSV = SV; + // for (i = LB; i <= min(AEV, UB); ++i) + // B; + // for (i = max(LB, BSV); i <= UB; ++i) + // A; + AEV = BinaryOperator::CreateSub(SD.SplitValue, + ConstantInt::get(Ty, 1, Sign), + "lsplit.sub", PHTerminator); + break; + default: + assert (0 && "Unexpected split condition predicate"); + break; + } // end switch (SP) + } + break; + } + + // Calculate ALoop induction variable's new exiting value and + // BLoop induction variable's new starting value. Calculuate these + // values in original loop's preheader. + // A_ExitValue = min(SplitValue, OrignalLoopExitValue) + // B_StartValue = max(SplitValue, OriginalLoopStartValue) + Instruction *InsertPt = L->getHeader()->getFirstNonPHI(); + + // If ExitValue operand is also defined in Loop header then + // insert new ExitValue after this operand definition. + if (Instruction *EVN = + dyn_cast(ExitCondition->getOperand(ExitValueNum))) { + if (!isa(EVN)) + if (InsertPt->getParent() == EVN->getParent()) { + BasicBlock::iterator LHBI = L->getHeader()->begin(); + BasicBlock::iterator LHBE = L->getHeader()->end(); + for(;LHBI != LHBE; ++LHBI) { + Instruction *I = LHBI; + if (I == EVN) + break; + } + InsertPt = ++LHBI; + } + } + Value *C1 = new ICmpInst(Sign ? + ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + AEV, + ExitCondition->getOperand(ExitValueNum), + "lsplit.ev", InsertPt); + + SD.A_ExitValue = SelectInst::Create(C1, AEV, + ExitCondition->getOperand(ExitValueNum), + "lsplit.ev", InsertPt); + + Value *C2 = new ICmpInst(Sign ? + ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + BSV, StartValue, "lsplit.sv", + PHTerminator); + SD.B_StartValue = SelectInst::Create(C2, StartValue, BSV, + "lsplit.sv", PHTerminator); +} + +/// splitLoop - Split current loop L in two loops using split information +/// SD. Update dominator information. Maintain LCSSA form. +bool LoopIndexSplit::splitLoop(SplitInfo &SD) { + + if (!safeSplitCondition(SD)) + return false; + + BasicBlock *SplitCondBlock = SD.SplitCondition->getParent(); + + // Unable to handle triange loops at the moment. + // In triangle loop, split condition is in header and one of the + // the split destination is loop latch. If split condition is EQ + // then such loops are already handle in processOneIterationLoop(). + BasicBlock *Latch = L->getLoopLatch(); + BranchInst *SplitTerminator = + cast(SplitCondBlock->getTerminator()); + BasicBlock *Succ0 = SplitTerminator->getSuccessor(0); + BasicBlock *Succ1 = SplitTerminator->getSuccessor(1); + if (L->getHeader() == SplitCondBlock + && (Latch == Succ0 || Latch == Succ1)) + return false; + + // If split condition branches heads do not have single predecessor, + // SplitCondBlock, then is not possible to remove inactive branch. + if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor()) + return false; + + // If Exiting block includes loop variant instructions then this + // loop may not be split safely. + if (!safeExitingBlock(SD, ExitCondition->getParent())) + return false; + + // After loop is cloned there are two loops. + // + // First loop, referred as ALoop, executes first part of loop's iteration + // space split. Second loop, referred as BLoop, executes remaining + // part of loop's iteration space. + // + // ALoop's exit edge enters BLoop's header through a forwarding block which + // acts as a BLoop's preheader. + BasicBlock *Preheader = L->getLoopPreheader(); + + // Calculate ALoop induction variable's new exiting value and + // BLoop induction variable's new starting value. + calculateLoopBounds(SD); + + //[*] Clone loop. + DenseMap ValueMap; + Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this); + Loop *ALoop = L; + BasicBlock *B_Header = BLoop->getHeader(); + + //[*] ALoop's exiting edge BLoop's header. + // ALoop's original exit block becomes BLoop's exit block. + PHINode *B_IndVar = cast(ValueMap[IndVar]); + BasicBlock *A_ExitingBlock = ExitCondition->getParent(); + BranchInst *A_ExitInsn = + dyn_cast(A_ExitingBlock->getTerminator()); + assert (A_ExitInsn && "Unable to find suitable loop exit branch"); + BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1); + if (L->contains(B_ExitBlock)) { + B_ExitBlock = A_ExitInsn->getSuccessor(0); + A_ExitInsn->setSuccessor(0, B_Header); + } else + A_ExitInsn->setSuccessor(1, B_Header); + + //[*] Update ALoop's exit value using new exit value. + ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue); + + // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from + // original loop's preheader. Add incoming PHINode values from + // ALoop's exiting block. Update BLoop header's domiantor info. + + // Collect inverse map of Header PHINodes. + DenseMap InverseMap; + for (BasicBlock::iterator BI = L->getHeader()->begin(), + BE = L->getHeader()->end(); BI != BE; ++BI) { + if (PHINode *PN = dyn_cast(BI)) { + PHINode *PNClone = cast(ValueMap[PN]); + InverseMap[PNClone] = PN; + } else + break; + } + + for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end(); + BI != BE; ++BI) { + if (PHINode *PN = dyn_cast(BI)) { + // Remove incoming value from original preheader. + PN->removeIncomingValue(Preheader); + + // Add incoming value from A_ExitingBlock. + if (PN == B_IndVar) + PN->addIncoming(SD.B_StartValue, A_ExitingBlock); + else { + PHINode *OrigPN = cast(InverseMap[PN]); + Value *V2 = NULL; + // If loop header is also loop exiting block then + // OrigPN is incoming value for B loop header. + if (A_ExitingBlock == L->getHeader()) + V2 = OrigPN; + else + V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock); + PN->addIncoming(V2, A_ExitingBlock); + } + } else + break; + } + DT->changeImmediateDominator(B_Header, A_ExitingBlock); + DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT); + + // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit + // block. Remove incoming PHINode values from ALoop's exiting block. + // Add new incoming values from BLoop's incoming exiting value. + // Update BLoop exit block's dominator info.. + BasicBlock *B_ExitingBlock = cast(ValueMap[A_ExitingBlock]); + for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end(); + BI != BE; ++BI) { + if (PHINode *PN = dyn_cast(BI)) { + PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)], + B_ExitingBlock); + PN->removeIncomingValue(A_ExitingBlock); + } else + break; + } + + DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock); + DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT); + + //[*] Split ALoop's exit edge. This creates a new block which + // serves two purposes. First one is to hold PHINode defnitions + // to ensure that ALoop's LCSSA form. Second use it to act + // as a preheader for BLoop. + BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this); + + //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes + // in A_ExitBlock to redefine outgoing PHI definitions from ALoop. + for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end(); + BI != BE; ++BI) { + if (PHINode *PN = dyn_cast(BI)) { + Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock); + PHINode *newPHI = PHINode::Create(PN->getType(), PN->getName()); + newPHI->addIncoming(V1, A_ExitingBlock); + A_ExitBlock->getInstList().push_front(newPHI); + PN->removeIncomingValue(A_ExitBlock); + PN->addIncoming(newPHI, A_ExitBlock); + } else + break; + } + + //[*] Eliminate split condition's inactive branch from ALoop. + BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent(); + BranchInst *A_BR = cast(A_SplitCondBlock->getTerminator()); + BasicBlock *A_InactiveBranch = NULL; + BasicBlock *A_ActiveBranch = NULL; + if (SD.UseTrueBranchFirst) { + A_ActiveBranch = A_BR->getSuccessor(0); + A_InactiveBranch = A_BR->getSuccessor(1); + } else { + A_ActiveBranch = A_BR->getSuccessor(1); + A_InactiveBranch = A_BR->getSuccessor(0); + } + A_BR->setUnconditionalDest(A_ActiveBranch); + removeBlocks(A_InactiveBranch, L, A_ActiveBranch); + + //[*] Eliminate split condition's inactive branch in from BLoop. + BasicBlock *B_SplitCondBlock = cast(ValueMap[A_SplitCondBlock]); + BranchInst *B_BR = cast(B_SplitCondBlock->getTerminator()); + BasicBlock *B_InactiveBranch = NULL; + BasicBlock *B_ActiveBranch = NULL; + if (SD.UseTrueBranchFirst) { + B_ActiveBranch = B_BR->getSuccessor(1); + B_InactiveBranch = B_BR->getSuccessor(0); + } else { + B_ActiveBranch = B_BR->getSuccessor(0); + B_InactiveBranch = B_BR->getSuccessor(1); + } + B_BR->setUnconditionalDest(B_ActiveBranch); + removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch); + + BasicBlock *A_Header = L->getHeader(); + if (A_ExitingBlock == A_Header) + return true; + + //[*] Move exit condition into split condition block to avoid + // executing dead loop iteration. + ICmpInst *B_ExitCondition = cast(ValueMap[ExitCondition]); + Instruction *B_IndVarIncrement = cast(ValueMap[IndVarIncrement]); + ICmpInst *B_SplitCondition = cast(ValueMap[SD.SplitCondition]); + + moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition, + cast(SD.SplitCondition), IndVar, IndVarIncrement, + ALoop); + + moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition, + B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop); + + return true; +} + +// moveExitCondition - Move exit condition EC into split condition block CondBB. +void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB, + BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC, + PHINode *IV, Instruction *IVAdd, Loop *LP) { + + BasicBlock *ExitingBB = EC->getParent(); + Instruction *CurrentBR = CondBB->getTerminator(); + + // Move exit condition into split condition block. + EC->moveBefore(CurrentBR); + EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV); + + // Move exiting block's branch into split condition block. Update its branch + // destination. + BranchInst *ExitingBR = cast(ExitingBB->getTerminator()); + ExitingBR->moveBefore(CurrentBR); + BasicBlock *OrigDestBB = NULL; + if (ExitingBR->getSuccessor(0) == ExitBB) { + OrigDestBB = ExitingBR->getSuccessor(1); + ExitingBR->setSuccessor(1, ActiveBB); + } + else { + OrigDestBB = ExitingBR->getSuccessor(0); + ExitingBR->setSuccessor(0, ActiveBB); + } + + // Remove split condition and current split condition branch. + SC->eraseFromParent(); + CurrentBR->eraseFromParent(); + + // Connect exiting block to original destination. + BranchInst::Create(OrigDestBB, ExitingBB); + + // Update PHINodes + updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd, LP); + + // Fix dominator info. + // ExitBB is now dominated by CondBB + DT->changeImmediateDominator(ExitBB, CondBB); + DF->changeImmediateDominator(ExitBB, CondBB, DT); + + // Basicblocks dominated by ActiveBB may have ExitingBB or + // a basic block outside the loop in their DF list. If so, + // replace it with CondBB. + DomTreeNode *Node = DT->getNode(ActiveBB); + for (df_iterator DI = df_begin(Node), DE = df_end(Node); + DI != DE; ++DI) { + BasicBlock *BB = DI->getBlock(); + DominanceFrontier::iterator BBDF = DF->find(BB); + DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin(); + DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end(); + while (DomSetI != DomSetE) { + DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI; + ++DomSetI; + BasicBlock *DFBB = *CurrentItr; + if (DFBB == ExitingBB || !L->contains(DFBB)) { + BBDF->second.erase(DFBB); + BBDF->second.insert(CondBB); + } + } + } +} + +/// updatePHINodes - CFG has been changed. +/// Before +/// - ExitBB's single predecessor was Latch +/// - Latch's second successor was Header +/// Now +/// - ExitBB's single predecessor is Header +/// - Latch's one and only successor is Header +/// +/// Update ExitBB PHINodes' to reflect this change. +void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch, + BasicBlock *Header, + PHINode *IV, Instruction *IVIncrement, + Loop *LP) { + + for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end(); + BI != BE; ) { + PHINode *PN = dyn_cast(BI); + ++BI; + if (!PN) + break; + + Value *V = PN->getIncomingValueForBlock(Latch); + if (PHINode *PHV = dyn_cast(V)) { + // PHV is in Latch. PHV has one use is in ExitBB PHINode. And one use + // in Header which is new incoming value for PN. + Value *NewV = NULL; + for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end(); + UI != E; ++UI) + if (PHINode *U = dyn_cast(*UI)) + if (LP->contains(U->getParent())) { + NewV = U; + break; + } + + // Add incoming value from header only if PN has any use inside the loop. + if (NewV) + PN->addIncoming(NewV, Header); + + } else if (Instruction *PHI = dyn_cast(V)) { + // If this instruction is IVIncrement then IV is new incoming value + // from header otherwise this instruction must be incoming value from + // header because loop is in LCSSA form. + if (PHI == IVIncrement) + PN->addIncoming(IV, Header); + else + PN->addIncoming(V, Header); + } else + // Otherwise this is an incoming value from header because loop is in + // LCSSA form. + PN->addIncoming(V, Header); + + // Remove incoming value from Latch. + PN->removeIncomingValue(Latch); + } +}