X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoopDependenceAnalysis.cpp;h=3997ac478b52cca1c0f60fbe0fd37b56d1056397;hb=21646e8becaa13cb813490edcd7fe9150b11f88e;hp=bf3978ec4e88fd453f0f480793ce9d9c50defb8c;hpb=5eca4525f42a99eec29be1676a7a77928853c521;p=oota-llvm.git diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp index bf3978ec4e8..3997ac478b5 100644 --- a/lib/Analysis/LoopDependenceAnalysis.cpp +++ b/lib/Analysis/LoopDependenceAnalysis.cpp @@ -20,12 +20,15 @@ //===----------------------------------------------------------------------===// #define DEBUG_TYPE "lda" +#include "llvm/ADT/DenseSet.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/LoopDependenceAnalysis.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolution.h" #include "llvm/Analysis/ScalarEvolutionExpressions.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/Assembly/Writer.h" #include "llvm/Instructions.h" #include "llvm/Operator.h" #include "llvm/Support/Allocator.h" @@ -45,8 +48,12 @@ LoopPass *llvm::createLoopDependenceAnalysisPass() { return new LoopDependenceAnalysis(); } -static RegisterPass -R("lda", "Loop Dependence Analysis", false, true); +INITIALIZE_PASS_BEGIN(LoopDependenceAnalysis, "lda", + "Loop Dependence Analysis", false, true) +INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) +INITIALIZE_AG_DEPENDENCY(AliasAnalysis) +INITIALIZE_PASS_END(LoopDependenceAnalysis, "lda", + "Loop Dependence Analysis", false, true) char LoopDependenceAnalysis::ID = 0; //===----------------------------------------------------------------------===// @@ -69,7 +76,13 @@ static void GetMemRefInstrs(const Loop *L, } static bool IsLoadOrStoreInst(Value *I) { - return isa(I) || isa(I); + // Returns true if the load or store can be analyzed. Atomic and volatile + // operations have properties which this analysis does not understand. + if (LoadInst *LI = dyn_cast(I)) + return LI->isUnordered(); + else if (StoreInst *SI = dyn_cast(I)) + return SI->isUnordered(); + return false; } static Value *GetPointerOperand(Value *I) { @@ -85,14 +98,14 @@ static Value *GetPointerOperand(Value *I) { static AliasAnalysis::AliasResult UnderlyingObjectsAlias(AliasAnalysis *AA, const Value *A, const Value *B) { - const Value *aObj = A->getUnderlyingObject(); - const Value *bObj = B->getUnderlyingObject(); + const Value *aObj = GetUnderlyingObject(A); + const Value *bObj = GetUnderlyingObject(B); return AA->alias(aObj, AA->getTypeStoreSize(aObj->getType()), bObj, AA->getTypeStoreSize(bObj->getType())); } static inline const SCEV *GetZeroSCEV(ScalarEvolution *SE) { - return SE->getConstant(Type::Int32Ty, 0L); + return SE->getConstant(Type::getInt32Ty(SE->getContext()), 0L); } //===----------------------------------------------------------------------===// @@ -118,17 +131,23 @@ bool LoopDependenceAnalysis::findOrInsertDependencePair(Value *A, P = Pairs.FindNodeOrInsertPos(id, insertPos); if (P) return true; - P = PairAllocator.Allocate(); - new (P) DependencePair(id, A, B); + P = new (PairAllocator) DependencePair(id, A, B); Pairs.InsertNode(P, insertPos); return false; } -bool LoopDependenceAnalysis::isLoopInvariant(const SCEV *S) const { +void LoopDependenceAnalysis::getLoops(const SCEV *S, + DenseSet* Loops) const { + // Refactor this into an SCEVVisitor, if efficiency becomes a concern. for (const Loop *L = this->L; L != 0; L = L->getParentLoop()) - if (!S->isLoopInvariant(L)) - return false; - return true; + if (!SE->isLoopInvariant(S, L)) + Loops->insert(L); +} + +bool LoopDependenceAnalysis::isLoopInvariant(const SCEV *S) const { + DenseSet loops; + getLoops(S, &loops); + return loops.empty(); } bool LoopDependenceAnalysis::isAffine(const SCEV *S) const { @@ -136,36 +155,72 @@ bool LoopDependenceAnalysis::isAffine(const SCEV *S) const { return isLoopInvariant(S) || (rec && rec->isAffine()); } +bool LoopDependenceAnalysis::isZIVPair(const SCEV *A, const SCEV *B) const { + return isLoopInvariant(A) && isLoopInvariant(B); +} + +bool LoopDependenceAnalysis::isSIVPair(const SCEV *A, const SCEV *B) const { + DenseSet loops; + getLoops(A, &loops); + getLoops(B, &loops); + return loops.size() == 1; +} + +LoopDependenceAnalysis::DependenceResult +LoopDependenceAnalysis::analyseZIV(const SCEV *A, + const SCEV *B, + Subscript *S) const { + assert(isZIVPair(A, B) && "Attempted to ZIV-test non-ZIV SCEVs!"); + return A == B ? Dependent : Independent; +} + +LoopDependenceAnalysis::DependenceResult +LoopDependenceAnalysis::analyseSIV(const SCEV *A, + const SCEV *B, + Subscript *S) const { + return Unknown; // TODO: Implement. +} + +LoopDependenceAnalysis::DependenceResult +LoopDependenceAnalysis::analyseMIV(const SCEV *A, + const SCEV *B, + Subscript *S) const { + return Unknown; // TODO: Implement. +} + LoopDependenceAnalysis::DependenceResult LoopDependenceAnalysis::analyseSubscript(const SCEV *A, const SCEV *B, Subscript *S) const { - DEBUG(errs() << " Testing subscript: " << *A << ", " << *B << "\n"); + DEBUG(dbgs() << " Testing subscript: " << *A << ", " << *B << "\n"); if (A == B) { - DEBUG(errs() << " -> [D] same SCEV\n"); + DEBUG(dbgs() << " -> [D] same SCEV\n"); return Dependent; } if (!isAffine(A) || !isAffine(B)) { - DEBUG(errs() << " -> [?] not affine\n"); + DEBUG(dbgs() << " -> [?] not affine\n"); return Unknown; } - // TODO: Implement ZIV/SIV/MIV testers. + if (isZIVPair(A, B)) + return analyseZIV(A, B, S); + + if (isSIVPair(A, B)) + return analyseSIV(A, B, S); - DEBUG(errs() << " -> [?] cannot analyse subscript\n"); - return Unknown; + return analyseMIV(A, B, S); } LoopDependenceAnalysis::DependenceResult LoopDependenceAnalysis::analysePair(DependencePair *P) const { - DEBUG(errs() << "Analysing:\n" << *P->A << "\n" << *P->B << "\n"); + DEBUG(dbgs() << "Analysing:\n" << *P->A << "\n" << *P->B << "\n"); // We only analyse loads and stores but no possible memory accesses by e.g. // free, call, or invoke instructions. if (!IsLoadOrStoreInst(P->A) || !IsLoadOrStoreInst(P->B)) { - DEBUG(errs() << "--> [?] no load/store\n"); + DEBUG(dbgs() << "--> [?] no load/store\n"); return Unknown; } @@ -174,13 +229,14 @@ LoopDependenceAnalysis::analysePair(DependencePair *P) const { switch (UnderlyingObjectsAlias(AA, aPtr, bPtr)) { case AliasAnalysis::MayAlias: + case AliasAnalysis::PartialAlias: // We can not analyse objects if we do not know about their aliasing. - DEBUG(errs() << "---> [?] may alias\n"); + DEBUG(dbgs() << "---> [?] may alias\n"); return Unknown; case AliasAnalysis::NoAlias: // If the objects noalias, they are distinct, accesses are independent. - DEBUG(errs() << "---> [I] no alias\n"); + DEBUG(dbgs() << "---> [I] no alias\n"); return Independent; case AliasAnalysis::MustAlias: @@ -195,28 +251,44 @@ LoopDependenceAnalysis::analysePair(DependencePair *P) const { // FIXME: Is filtering coupled subscripts necessary? - // Analyse indices pairwise (FIXME: use GetGEPOperands from BasicAA), adding + // Collect GEP operand pairs (FIXME: use GetGEPOperands from BasicAA), adding // trailing zeroes to the smaller GEP, if needed. - GEPOperator::const_op_iterator aIdx = aGEP->idx_begin(), - aEnd = aGEP->idx_end(), - bIdx = bGEP->idx_begin(), - bEnd = bGEP->idx_end(); - while (aIdx != aEnd && bIdx != bEnd) { + typedef SmallVector, 4> GEPOpdPairsTy; + GEPOpdPairsTy opds; + for(GEPOperator::const_op_iterator aIdx = aGEP->idx_begin(), + aEnd = aGEP->idx_end(), + bIdx = bGEP->idx_begin(), + bEnd = bGEP->idx_end(); + aIdx != aEnd && bIdx != bEnd; + aIdx += (aIdx != aEnd), bIdx += (bIdx != bEnd)) { const SCEV* aSCEV = (aIdx != aEnd) ? SE->getSCEV(*aIdx) : GetZeroSCEV(SE); const SCEV* bSCEV = (bIdx != bEnd) ? SE->getSCEV(*bIdx) : GetZeroSCEV(SE); + opds.push_back(std::make_pair(aSCEV, bSCEV)); + } + + if (!opds.empty() && opds[0].first != opds[0].second) { + // We cannot (yet) handle arbitrary GEP pointer offsets. By limiting + // + // TODO: this could be relaxed by adding the size of the underlying object + // to the first subscript. If we have e.g. (GEP x,0,i; GEP x,2,-i) and we + // know that x is a [100 x i8]*, we could modify the first subscript to be + // (i, 200-i) instead of (i, -i). + return Unknown; + } + + // Now analyse the collected operand pairs (skipping the GEP ptr offsets). + for (GEPOpdPairsTy::const_iterator i = opds.begin() + 1, end = opds.end(); + i != end; ++i) { Subscript subscript; - DependenceResult result = analyseSubscript(aSCEV, bSCEV, &subscript); + DependenceResult result = analyseSubscript(i->first, i->second, &subscript); if (result != Dependent) { // We either proved independence or failed to analyse this subscript. // Further subscripts will not improve the situation, so abort early. return result; } P->Subscripts.push_back(subscript); - if (aIdx != aEnd) ++aIdx; - if (bIdx != bEnd) ++bIdx; } - // Either there were no subscripts or all subscripts were analysed to be - // dependent; in both cases we know the accesses are dependent. + // We successfully analysed all subscripts but failed to prove independence. return Dependent; } @@ -290,8 +362,3 @@ void LoopDependenceAnalysis::print(raw_ostream &OS, const Module*) const { // TODO: doc why const_cast is safe PrintLoopInfo(OS, const_cast(this), this->L); } - -void LoopDependenceAnalysis::print(std::ostream &OS, const Module *M) const { - raw_os_ostream os(OS); - print(os, M); -}