X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoopDependenceAnalysis.cpp;h=32d22662c341586e2be6a5a51c8d9a37e17da650;hb=1134dc5cc0cb83abcdf072dc4300cd7a898f830c;hp=8f3e6baf5c57596f06ec714dfcb8928a71aed996;hpb=707207adaed969c32a09ae873ac5a171b3744617;p=oota-llvm.git diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp index 8f3e6baf5c5..32d22662c34 100644 --- a/lib/Analysis/LoopDependenceAnalysis.cpp +++ b/lib/Analysis/LoopDependenceAnalysis.cpp @@ -15,14 +15,33 @@ // // 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/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(); } @@ -31,35 +50,303 @@ static RegisterPass R("lda", "Loop Dependence Analysis", false, true); char LoopDependenceAnalysis::ID = 0; +//===----------------------------------------------------------------------===// +// Utility Functions +//===----------------------------------------------------------------------===// + +static inline bool IsMemRefInstr(const Value *V) { + const Instruction *I = dyn_cast(V); + return I && (I->mayReadFromMemory() || I->mayWriteToMemory()); +} + +static void GetMemRefInstrs(const Loop *L, + SmallVectorImpl &Memrefs) { + for (Loop::block_iterator b = L->block_begin(), be = L->block_end(); + b != be; ++b) + for (BasicBlock::iterator i = (*b)->begin(), ie = (*b)->end(); + i != ie; ++i) + if (IsMemRefInstr(i)) + Memrefs.push_back(i); +} + +static bool IsLoadOrStoreInst(Value *I) { + return isa(I) || isa(I); +} + +static Value *GetPointerOperand(Value *I) { + if (LoadInst *i = dyn_cast(I)) + return i->getPointerOperand(); + if (StoreInst *i = dyn_cast(I)) + return i->getPointerOperand(); + llvm_unreachable("Value is no load or store instruction!"); + // Never reached. + return 0; +} + +static AliasAnalysis::AliasResult UnderlyingObjectsAlias(AliasAnalysis *AA, + const Value *A, + const Value *B) { + const Value *aObj = A->getUnderlyingObject(); + const Value *bObj = B->getUnderlyingObject(); + 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 +//===----------------------------------------------------------------------===// + +bool LoopDependenceAnalysis::isDependencePair(const Value *A, + const Value *B) const { + return IsMemRefInstr(A) && + IsMemRefInstr(B) && + (cast(A)->mayWriteToMemory() || + cast(B)->mayWriteToMemory()); +} + +bool LoopDependenceAnalysis::findOrInsertDependencePair(Value *A, + Value *B, + DependencePair *&P) { + void *insertPos = 0; + FoldingSetNodeID id; + id.AddPointer(A); + id.AddPointer(B); + + P = Pairs.FindNodeOrInsertPos(id, insertPos); + if (P) return true; + + P = PairAllocator.Allocate(); + new (P) DependencePair(id, A, B); + Pairs.InsertNode(P, insertPos); + return false; +} + +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)) + 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 { + 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(errs() << " Testing subscript: " << *A << ", " << *B << "\n"); + + if (A == B) { + DEBUG(errs() << " -> [D] same SCEV\n"); + return Dependent; + } + + if (!isAffine(A) || !isAffine(B)) { + DEBUG(errs() << " -> [?] 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(errs() << "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"); + return Unknown; + } + + Value *aPtr = GetPointerOperand(P->A); + Value *bPtr = GetPointerOperand(P->B); + + switch (UnderlyingObjectsAlias(AA, aPtr, bPtr)) { + case AliasAnalysis::MayAlias: + // We can not analyse objects if we do not know about their aliasing. + DEBUG(errs() << "---> [?] may alias\n"); + return Unknown; + + case AliasAnalysis::NoAlias: + // If the objects noalias, they are distinct, accesses are independent. + DEBUG(errs() << "---> [I] no alias\n"); + return Independent; + + case AliasAnalysis::MustAlias: + break; // The underlying objects alias, test accesses for dependence. + } + + 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)); + } + + 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(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. + ++NumAnalysed; + switch (p->Result = analysePair(p)) { + case Dependent: ++NumDependent; break; + case Independent: ++NumIndependent; break; + case Unknown: ++NumUnknown; break; + } + } + return p->Result != Independent; +} + //===----------------------------------------------------------------------===// // LoopDependenceAnalysis Implementation //===----------------------------------------------------------------------===// bool LoopDependenceAnalysis::runOnLoop(Loop *L, LPPassManager &) { this->L = L; + AA = &getAnalysis(); SE = &getAnalysis(); return false; } +void LoopDependenceAnalysis::releaseMemory() { + Pairs.clear(); + PairAllocator.Reset(); +} + void LoopDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); + AU.addRequiredTransitive(); AU.addRequiredTransitive(); } -static void PrintLoopInfo( - raw_ostream &OS, const LoopDependenceAnalysis *LDA, const Loop *L) { +static void PrintLoopInfo(raw_ostream &OS, + LoopDependenceAnalysis *LDA, const Loop *L) { if (!L->empty()) return; // ignore non-innermost loops + SmallVector memrefs; + GetMemRefInstrs(L, memrefs); + OS << "Loop at depth " << L->getLoopDepth() << ", header block: "; WriteAsOperand(OS, L->getHeader(), false); OS << "\n"; -} -void LoopDependenceAnalysis::print(raw_ostream &OS, const Module*) const { - PrintLoopInfo(OS, this, this->L); + OS << " Load/store instructions: " << memrefs.size() << "\n"; + for (SmallVector::const_iterator x = memrefs.begin(), + 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) + for (SmallVector::const_iterator y = x + 1; + y != end; ++y) + if (LDA->isDependencePair(*x, *y)) + OS << "\t" << (x - memrefs.begin()) << "," << (y - memrefs.begin()) + << ": " << (LDA->depends(*x, *y) ? "dependent" : "independent") + << "\n"; } -void LoopDependenceAnalysis::print(std::ostream &OS, const Module *M) const { - raw_os_ostream os(OS); - print(os, M); +void LoopDependenceAnalysis::print(raw_ostream &OS, const Module*) const { + // TODO: doc why const_cast is safe + PrintLoopInfo(OS, const_cast(this), this->L); }