diff --git a/include/llvm/Analysis/LoopAccessAnalysis.h b/include/llvm/Analysis/LoopAccessAnalysis.h index e05f99726f2..937718b5408 100644 --- a/include/llvm/Analysis/LoopAccessAnalysis.h +++ b/include/llvm/Analysis/LoopAccessAnalysis.h @@ -179,6 +179,10 @@ private: /// \brief Analyze the loop. Substitute symbolic strides using Strides. void analyzeLoop(ValueToValueMap &Strides); + /// \brief Check if the structure of the loop allows it to be analyzed by this + /// pass. + bool canAnalyzeLoop(); + void emitAnalysis(VectorizationReport &Message); /// We need to check that all of the pointers in this list are disjoint diff --git a/lib/Analysis/LoopAccessAnalysis.cpp b/lib/Analysis/LoopAccessAnalysis.cpp index e9e9be31ff7..ba2f9b8e427 100644 --- a/lib/Analysis/LoopAccessAnalysis.cpp +++ b/lib/Analysis/LoopAccessAnalysis.cpp @@ -830,6 +830,55 @@ bool MemoryDepChecker::areDepsSafe(AccessAnalysis::DepCandidates &AccessSets, return true; } +bool LoopAccessInfo::canAnalyzeLoop() { + // We can only analyze innermost loops. + if (!TheLoop->empty()) { + emitAnalysis(VectorizationReport() << "loop is not the innermost loop"); + return false; + } + + // We must have a single backedge. + if (TheLoop->getNumBackEdges() != 1) { + emitAnalysis( + VectorizationReport() << + "loop control flow is not understood by analyzer"); + return false; + } + + // We must have a single exiting block. + if (!TheLoop->getExitingBlock()) { + emitAnalysis( + VectorizationReport() << + "loop control flow is not understood by analyzer"); + return false; + } + + // We only handle bottom-tested loops, i.e. loop in which the condition is + // checked at the end of each iteration. With that we can assume that all + // instructions in the loop are executed the same number of times. + if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) { + emitAnalysis( + VectorizationReport() << + "loop control flow is not understood by analyzer"); + return false; + } + + // We need to have a loop header. + DEBUG(dbgs() << "LAA: Found a loop: " << + TheLoop->getHeader()->getName() << '\n'); + + // ScalarEvolution needs to be able to find the exit count. + const SCEV *ExitCount = SE->getBackedgeTakenCount(TheLoop); + if (ExitCount == SE->getCouldNotCompute()) { + emitAnalysis(VectorizationReport() << + "could not determine number of loop iterations"); + DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n"); + return false; + } + + return true; +} + void LoopAccessInfo::analyzeLoop(ValueToValueMap &Strides) { typedef SmallVector ValueVector; @@ -1213,7 +1262,8 @@ LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE, DominatorTree *DT, ValueToValueMap &Strides) : TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA), DT(DT), NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1U), CanVecMem(false) { - analyzeLoop(Strides); + if (canAnalyzeLoop()) + analyzeLoop(Strides); } LoopAccessInfo &LoopAccessAnalysis::getInfo(Loop *L, ValueToValueMap &Strides) {