X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoopDependenceAnalysis.cpp;h=10a6a8eb06f500bdedbf6909a32526ac9d04777f;hb=c9008c5cc7113ea4c3a262e346c0dfcdbca12ae6;hp=f6057839266f277b602c50ffcd623aab90679fef;hpb=292aef33e1ed71e720f4e8d0b7332a1013398836;p=oota-llvm.git diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp index f6057839266..10a6a8eb06f 100644 --- a/lib/Analysis/LoopDependenceAnalysis.cpp +++ b/lib/Analysis/LoopDependenceAnalysis.cpp @@ -15,18 +15,32 @@ // // TODO: adapt as implementation progresses. // +// TODO: document lingo (pair, subscript, index) +// //===----------------------------------------------------------------------===// #define DEBUG_TYPE "lda" +#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(); } @@ -44,14 +58,14 @@ static inline bool IsMemRefInstr(const Value *V) { return I && (I->mayReadFromMemory() || I->mayWriteToMemory()); } -static void GetMemRefInstrs( - const Loop *L, SmallVectorImpl &memrefs) { +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); + Memrefs.push_back(i); } static bool IsLoadOrStoreInst(Value *I) { @@ -63,53 +77,196 @@ static Value *GetPointerOperand(Value *I) { return i->getPointerOperand(); if (StoreInst *i = dyn_cast(I)) return i->getPointerOperand(); - assert(0 && "Value is no load or store instruction!"); + 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::Int32Ty, 0L); +} + //===----------------------------------------------------------------------===// // Dependence Testing //===----------------------------------------------------------------------===// -bool LoopDependenceAnalysis::isDependencePair(const Value *x, - const Value *y) const { - return IsMemRefInstr(x) && - IsMemRefInstr(y) && - (cast(x)->mayWriteToMemory() || - cast(y)->mayWriteToMemory()); +bool LoopDependenceAnalysis::isDependencePair(const Value *A, + const Value *B) const { + return IsMemRefInstr(A) && + IsMemRefInstr(B) && + (cast(A)->mayWriteToMemory() || + cast(B)->mayWriteToMemory()); } -bool LoopDependenceAnalysis::depends(Value *src, Value *dst) { - assert(isDependencePair(src, dst) && "Values form no dependence pair!"); - DOUT << "== LDA test ==\n" << *src << *dst; +bool LoopDependenceAnalysis::findOrInsertDependencePair(Value *A, + Value *B, + DependencePair *&P) { + void *insertPos = 0; + FoldingSetNodeID id; + id.AddPointer(A); + id.AddPointer(B); - // We only analyse loads and stores; for possible memory accesses by e.g. - // free, call, or invoke instructions we conservatively assume dependence. - if (!IsLoadOrStoreInst(src) || !IsLoadOrStoreInst(dst)) - return true; + P = Pairs.FindNodeOrInsertPos(id, insertPos); + if (P) return true; - Value *srcPtr = GetPointerOperand(src); - Value *dstPtr = GetPointerOperand(dst); - const Value *srcObj = srcPtr->getUnderlyingObject(); - const Value *dstObj = dstPtr->getUnderlyingObject(); - AliasAnalysis::AliasResult alias = AA->alias( - srcObj, AA->getTargetData().getTypeStoreSize(srcObj->getType()), - dstObj, AA->getTargetData().getTypeStoreSize(dstObj->getType())); + P = PairAllocator.Allocate(); + new (P) DependencePair(id, A, B); + Pairs.InsertNode(P, insertPos); + return false; +} - // If we don't know whether or not the two objects alias, assume dependence. - if (alias == AliasAnalysis::MayAlias) - return true; +bool LoopDependenceAnalysis::isLoopInvariant(const SCEV *S) const { + for (const Loop *L = this->L; L != 0; L = L->getParentLoop()) + if (!S->isLoopInvariant(L)) + return false; + return true; +} - // If the objects noalias, they are distinct, accesses are independent. - if (alias == AliasAnalysis::NoAlias) - return false; +bool LoopDependenceAnalysis::isAffine(const SCEV *S) const { + const SCEVAddRecExpr *rec = dyn_cast(S); + return isLoopInvariant(S) || (rec && rec->isAffine()); +} - // TODO: the underlying objects MustAlias, test for dependence +bool LoopDependenceAnalysis::isZIVPair(const SCEV *A, const SCEV *B) const { + return isLoopInvariant(A) && isLoopInvariant(B); +} - // We couldn't establish a more precise result, so we have to conservatively - // assume full dependence. - return true; +LoopDependenceAnalysis::DependenceResult +LoopDependenceAnalysis::analyseZIV(const SCEV *A, + const SCEV *B, + Subscript *S) const { + assert(isZIVPair(A, B)); + const SCEV *diff = SE->getMinusSCEV(A, B); + return diff->isZero() ? Dependent : Independent; +} + +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); + + // TODO: Implement SIV/MIV testers. + + DEBUG(errs() << " -> [?] cannot analyse subscript\n"); + return Unknown; +} + +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; } //===----------------------------------------------------------------------===// @@ -123,14 +280,19 @@ bool LoopDependenceAnalysis::runOnLoop(Loop *L, LPPassManager &) { 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, 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; @@ -142,14 +304,14 @@ static void PrintLoopInfo( 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; + 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")