diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp index bf3978ec4e8..5d593a97bf3 100644 --- a/lib/Analysis/LoopDependenceAnalysis.cpp +++ b/lib/Analysis/LoopDependenceAnalysis.cpp @@ -195,28 +195,44 @@ 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; }