From c70106cb30a0dc2e66905515349ab3382dc97602 Mon Sep 17 00:00:00 2001 From: Devang Patel Date: Tue, 7 Aug 2007 00:25:56 +0000 Subject: [PATCH] Begin loop index split pass. llvm-svn: 40883 --- llvm/include/llvm/LinkAllPasses.h | 1 + llvm/include/llvm/Transforms/Scalar.h | 6 + llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp | 384 ++++++++++++++++++ 3 files changed, 391 insertions(+) create mode 100644 llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp diff --git a/llvm/include/llvm/LinkAllPasses.h b/llvm/include/llvm/LinkAllPasses.h index 20cf28dd0d86..de99002fee56 100644 --- a/llvm/include/llvm/LinkAllPasses.h +++ b/llvm/include/llvm/LinkAllPasses.h @@ -83,6 +83,7 @@ namespace { (void) llvm::createLoopUnrollPass(); (void) llvm::createLoopUnswitchPass(); (void) llvm::createLoopRotatePass(); + (void) llvm::createLoopIndexSplitPass(); (void) llvm::createLowerAllocationsPass(); (void) llvm::createLowerGCPass(); (void) llvm::createLowerInvokePass(); diff --git a/llvm/include/llvm/Transforms/Scalar.h b/llvm/include/llvm/Transforms/Scalar.h index 94ad3764009d..7ba7ce85092e 100644 --- a/llvm/include/llvm/Transforms/Scalar.h +++ b/llvm/include/llvm/Transforms/Scalar.h @@ -141,6 +141,12 @@ LoopPass *createLoopUnrollPass(); // LoopPass *createLoopRotatePass(); +//===----------------------------------------------------------------------===// +// +// LoopIndexSplit - This pass splits loop +// +LoopPass *createLoopIndexSplitPass(); + //===----------------------------------------------------------------------===// // diff --git a/llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp b/llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp new file mode 100644 index 000000000000..a5dc4b09abe8 --- /dev/null +++ b/llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp @@ -0,0 +1,384 @@ +//===- LoopIndexSplit.cpp - Loop Index Splitting Pass ---------------------===// +// +// 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 implements Loop Index Splitting Pass. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "loop-index-split" + +#include "llvm/Function.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/Support/Compiler.h" +#include "llvm/ADT/Statistic.h" + +using namespace llvm; + +STATISTIC(NumIndexSplit, "Number of loops index split"); + +namespace { + + class VISIBILITY_HIDDEN LoopIndexSplit : public LoopPass { + + public: + static char ID; // Pass ID, replacement for typeid + LoopIndexSplit() : LoopPass((intptr_t)&ID) {} + + // Index split Loop L. Return true if loop is split. + bool runOnLoop(Loop *L, LPPassManager &LPM); + + void getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired(); + AU.addPreserved(); + AU.addRequiredID(LCSSAID); + AU.addPreservedID(LCSSAID); + AU.addPreserved(); + AU.addRequiredID(LoopSimplifyID); + AU.addPreservedID(LoopSimplifyID); + } + + private: + /// Find condition inside a loop that is suitable candidate for index split. + void findSplitCondition(); + + /// 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(); + + private: + + // Current Loop. + Loop *L; + ScalarEvolution *SE; + + // 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; + }; + + char LoopIndexSplit::ID = 0; + 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 Changed = false; + L = IncomingLoop; + SplitCondition = NULL; + SE = &getAnalysis(); + + findSplitCondition(); + + if (!SplitCondition) + return false; + + if (SplitCondition->getPredicate() == ICmpInst::ICMP_EQ) + // If it is possible to eliminate loop then do so. + Changed = processOneIterationLoop(LPM); + else + Changed = splitLoop(); + + if (Changed) + ++NumIndexSplit; + + return Changed; +} + +/// Find condition inside a loop that is suitable candidate for index split. +void LoopIndexSplit::findSplitCondition() { + + BasicBlock *Header = L->getHeader(); + + for (BasicBlock::iterator I = Header->begin(); isa(I); ++I) { + PHINode *PN = cast(I); + + if (!PN->getType()->isInteger()) + continue; + + SCEVHandle SCEV = SE->getSCEV(PN); + if (!isa(SCEV)) + 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; + } + } + + // 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 SplitValue is not invariant then SplitCondition is not appropriate. + if (!ValueSCEV->isLoopInvariant(L)) + SplitCondition = NULL; + } + + // We are looking for only one split condition. + if (SplitCondition) { + IndVar = PN; + break; + } + } +} + +/// processOneIterationLoop - Current loop L contains compare instruction +/// that compares induction variable, IndVar, against loop invariant. If +/// entire (i.e. meaningful) loop body is dominated by this compare +/// instruction then loop body is executed only once. In such case eliminate +/// loop structure surrounding this loop body. For example, +/// for (int i = start; i < end; ++i) { +/// if ( i == somevalue) { +/// loop_body +/// } +/// } +/// can be transformed into +/// if (somevalue >= start && somevalue < end) { +/// i = somevalue; +/// loop_body +/// } +bool LoopIndexSplit::processOneIterationLoop(LPPassManager &LPM) { + + BasicBlock *Header = L->getHeader(); + + // First of all, 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 (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)) + return false; + + // If Exit block includes loop variant instructions then this + // loop may not be eliminated. + if (!safeExitBlock(ExitBlock)) + return false; + + BasicBlock *Latch = L->getLoopLatch(); + BasicBlock *Preheader = L->getLoopPreheader(); + Instruction *Terminator = Header->getTerminator(); + Value *StartValue = IndVar->getIncomingValueForBlock(Preheader); + + // Update CFG. + + // 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 + // and i32 c1, c2 + bool SignedPredicate = SplitCondition->isSignedPredicate(); + Instruction *C1 = new ICmpInst(SignedPredicate ? + ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE, + SplitValue, StartValue, "lisplit", Terminator); + Instruction *C2 = new ICmpInst(SignedPredicate ? + ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, + SplitValue, ExitValue, "lisplit", Terminator); + Instruction *NSplitCond = BinaryOperator::create(Instruction::And, + C1, C2, "lisplit", Terminator); + SplitCondition->replaceAllUsesWith(NSplitCond); + SplitCondition->removeFromParent(); + delete SplitCondition; + + // As a first step to break this loop, 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) { + if (Header != *SI) + LatchSucc = *SI; + } + BranchInst *BR = dyn_cast(Latch->getTerminator()); + BR->setUnconditionalDest(LatchSucc); + + // Now, clear latch block. Remove instructions that are responsible + // to increment induction variable. + Instruction *LTerminator = Latch->getTerminator(); + for (BasicBlock::iterator LB = Latch->begin(), LE = Latch->end(); + LB != LE; ) { + Instruction *I = LB; + ++LB; + if (isa(I) || I == LTerminator) + continue; + + I->replaceAllUsesWith(UndefValue::get(I->getType())); + I->removeFromParent(); + delete I; + } + + LPM.deleteLoopFromQueue(L); + 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) { + + 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 (ICmpInst *CI = dyn_cast(I)) { + if (CI == SplitCondition) + continue; + } + + // Terminator is also harmless. + if (I == Terminator) + continue; + + // Otherwise we have a instruction that may not be safe. + return false; + } + + return true; +} + +// If Exit block includes loop variant instructions then this +// loop may not be eliminated. This is used by processOneIterationLoop(). +bool LoopIndexSplit::safeExitBlock(BasicBlock *ExitBlock) { + + Instruction *ExitCondition = NULL; + Instruction *IndVarIncrement = NULL; + + for (BasicBlock::iterator BI = ExitBlock->begin(), BE = ExitBlock->end(); + BI != BE; ++BI) { + Instruction *I = BI; + + // PHI Nodes are OK. + if (isa(I)) + continue; + + // Check if I is induction variable increment instruction. + if (BinaryOperator *BOp = dyn_cast(I)) { + if (BOp->getOpcode() != Instruction::Add) + return false; + + Value *Op0 = BOp->getOperand(0); + Value *Op1 = BOp->getOperand(1); + PHINode *PN = NULL; + ConstantInt *CI = NULL; + + if ((PN = dyn_cast(Op0))) { + if ((CI = dyn_cast(Op1))) + IndVarIncrement = I; + } else + if ((PN = dyn_cast(Op1))) { + if ((CI = dyn_cast(Op0))) + IndVarIncrement = I; + } + + 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 (isa(I)) { + ++BI; + Instruction *N = BI; + if (N == ExitBlock->getTerminator()) { + ExitCondition = I; + break; + } + } + + // 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); + + Instruction *Insn0 = dyn_cast(Op0); + Instruction *Insn1 = dyn_cast(Op1); + + if (Insn0 && Insn0 == IndVarIncrement) + ExitValue = Op1; + else if (Insn1 && Insn1 == IndVarIncrement) + ExitValue = Op0; + + SCEVHandle ValueSCEV = SE->getSCEV(ExitValue); + if (!ValueSCEV->isLoopInvariant(L)) + return false; + } + + // We could not find any reason to consider ExitBlock unsafe. + return true; +} + +bool LoopIndexSplit::splitLoop() { + // FIXME :) + return false; +}