X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoopDependenceAnalysis.cpp;h=c1afe8fbd61834da3573c1a07a2eea09a46a791a;hb=dcfd404e3ccc66844632aa601bf52522dae41512;hp=13d449f64ecdd8791135479b137b1cf1aef3dbde;hpb=b4c28e97f4cccd6ec8b816183bada8d0845a8966;p=oota-llvm.git diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp index 13d449f64ec..c1afe8fbd61 100644 --- a/lib/Analysis/LoopDependenceAnalysis.cpp +++ b/lib/Analysis/LoopDependenceAnalysis.cpp @@ -15,25 +15,45 @@ // // TODO: adapt as implementation progresses. // +// TODO: document lingo (pair, subscript, index) +// //===----------------------------------------------------------------------===// #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" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/raw_ostream.h" #include "llvm/Target/TargetData.h" using namespace llvm; +STATISTIC(NumAnswered, "Number of dependence queries answered"); +STATISTIC(NumAnalysed, "Number of distinct dependence pairs analysed"); +STATISTIC(NumDependent, "Number of pairs with dependent accesses"); +STATISTIC(NumIndependent, "Number of pairs with independent accesses"); +STATISTIC(NumUnknown, "Number of pairs with unknown accesses"); + 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; //===----------------------------------------------------------------------===// @@ -48,9 +68,9 @@ static inline bool IsMemRefInstr(const Value *V) { static void GetMemRefInstrs(const Loop *L, SmallVectorImpl &Memrefs) { for (Loop::block_iterator b = L->block_begin(), be = L->block_end(); - b != be; ++b) + b != be; ++b) for (BasicBlock::iterator i = (*b)->begin(), ie = (*b)->end(); - i != ie; ++i) + i != ie; ++i) if (IsMemRefInstr(i)) Memrefs.push_back(i); } @@ -69,6 +89,19 @@ static Value *GetPointerOperand(Value *I) { return 0; } +static AliasAnalysis::AliasResult UnderlyingObjectsAlias(AliasAnalysis *AA, + const Value *A, + const Value *B) { + 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::getInt32Ty(SE->getContext()), 0L); +} + //===----------------------------------------------------------------------===// // Dependence Testing //===----------------------------------------------------------------------===// @@ -81,71 +114,191 @@ bool LoopDependenceAnalysis::isDependencePair(const Value *A, cast(B)->mayWriteToMemory()); } -bool LoopDependenceAnalysis::findOrInsertDependencePair(Value *X, - Value *Y, +bool LoopDependenceAnalysis::findOrInsertDependencePair(Value *A, + Value *B, DependencePair *&P) { void *insertPos = 0; FoldingSetNodeID id; - id.AddPointer(X); - id.AddPointer(Y); + id.AddPointer(A); + id.AddPointer(B); P = Pairs.FindNodeOrInsertPos(id, insertPos); if (P) return true; - P = PairAllocator.Allocate(); - new (P) DependencePair(id, X, Y); + P = new (PairAllocator) DependencePair(id, A, B); Pairs.InsertNode(P, insertPos); return false; } -void LoopDependenceAnalysis::analysePair(DependencePair *P) const { - DOUT << "Analysing:\n" << *P->A << "\n" << *P->B << "\n"; +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 (!SE->isLoopInvariant(S, L)) + Loops->insert(L); +} - // Our default answer: we don't know anything, i.e. we failed to analyse this - // pair to get a more specific answer (dependent, independent). - P->Result = Unknown; +bool LoopDependenceAnalysis::isLoopInvariant(const SCEV *S) const { + DenseSet loops; + getLoops(S, &loops); + return loops.empty(); +} + +bool LoopDependenceAnalysis::isAffine(const SCEV *S) const { + const SCEVAddRecExpr *rec = dyn_cast(S); + 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(dbgs() << " Testing subscript: " << *A << ", " << *B << "\n"); + + if (A == B) { + DEBUG(dbgs() << " -> [D] same SCEV\n"); + return Dependent; + } + + if (!isAffine(A) || !isAffine(B)) { + DEBUG(dbgs() << " -> [?] not affine\n"); + return Unknown; + } + + if (isZIVPair(A, B)) + return analyseZIV(A, B, S); + + if (isSIVPair(A, B)) + return analyseSIV(A, B, S); + + return analyseMIV(A, B, S); +} + +LoopDependenceAnalysis::DependenceResult +LoopDependenceAnalysis::analysePair(DependencePair *P) const { + 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)) { - DOUT << "--> [?] no load/store\n"; - return; + DEBUG(dbgs() << "--> [?] no load/store\n"); + return Unknown; } - Value *aptr = GetPointerOperand(P->A); - Value *bptr = GetPointerOperand(P->B); - const Value *aobj = aptr->getUnderlyingObject(); - const Value *bobj = bptr->getUnderlyingObject(); - AliasAnalysis::AliasResult alias = AA->alias( - aobj, AA->getTargetData().getTypeStoreSize(aobj->getType()), - bobj, AA->getTargetData().getTypeStoreSize(bobj->getType())); - - // We can not analyse objects if we do not know about their aliasing. - if (alias == AliasAnalysis::MayAlias) { - DOUT << "---> [?] may alias\n"; - return; + Value *aPtr = GetPointerOperand(P->A); + Value *bPtr = GetPointerOperand(P->B); + + 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(dbgs() << "---> [?] may alias\n"); + return Unknown; + + case AliasAnalysis::NoAlias: + // If the objects noalias, they are distinct, accesses are independent. + DEBUG(dbgs() << "---> [I] no alias\n"); + return Independent; + + case AliasAnalysis::MustAlias: + break; // The underlying objects alias, test accesses for dependence. } - // If the objects noalias, they are distinct, accesses are independent. - if (alias == AliasAnalysis::NoAlias) { - DOUT << "---> [I] no alias\n"; - P->Result = Independent; - return; + const GEPOperator *aGEP = dyn_cast(aPtr); + const GEPOperator *bGEP = dyn_cast(bPtr); + + if (!aGEP || !bGEP) + return Unknown; + + // FIXME: Is filtering coupled subscripts necessary? + + // Collect GEP operand pairs (FIXME: use GetGEPOperands from BasicAA), adding + // trailing zeroes to the smaller GEP, if needed. + 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)); } - // TODO: the underlying objects MustAlias, test for dependence + 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; + } - DOUT << "---> [?] cannot analyse\n"; - return; + // 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(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); + } + // We successfully analysed all subscripts but failed to prove independence. + return Dependent; } bool LoopDependenceAnalysis::depends(Value *A, Value *B) { assert(isDependencePair(A, B) && "Values form no dependence pair!"); + ++NumAnswered; DependencePair *p; if (!findOrInsertDependencePair(A, B, p)) { // The pair is not cached, so analyse it. - analysePair(p); + ++NumAnalysed; + switch (p->Result = analysePair(p)) { + case Dependent: ++NumDependent; break; + case Independent: ++NumIndependent; break; + case Unknown: ++NumUnknown; break; + } } return p->Result != Independent; } @@ -185,14 +338,14 @@ static void PrintLoopInfo(raw_ostream &OS, OS << " Load/store instructions: " << memrefs.size() << "\n"; for (SmallVector::const_iterator x = memrefs.begin(), - end = memrefs.end(); x != end; ++x) + end = memrefs.end(); x != end; ++x) OS << "\t" << (x - memrefs.begin()) << ": " << **x << "\n"; OS << " Pairwise dependence results:\n"; for (SmallVector::const_iterator x = memrefs.begin(), - end = memrefs.end(); x != end; ++x) + end = memrefs.end(); x != end; ++x) for (SmallVector::const_iterator y = x + 1; - y != end; ++y) + y != end; ++y) if (LDA->isDependencePair(*x, *y)) OS << "\t" << (x - memrefs.begin()) << "," << (y - memrefs.begin()) << ": " << (LDA->depends(*x, *y) ? "dependent" : "independent") @@ -203,8 +356,3 @@ 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); -}