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SLPVectorizer: limit the number of alias checks to reduce the runtime.
In case of blocks with many memory-accessing instructions, alias checking can take lot of time (because calculating the memory dependencies has quadratic complexity). I chose a limit which resulted in no changes when running the benchmarks. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226439 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -75,6 +75,10 @@ static const unsigned MinVecRegSize = 128;
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static const unsigned RecursionMaxDepth = 12;
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static const unsigned RecursionMaxDepth = 12;
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// Limit the number of alias checks. The limit is chosen so that
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// it has no negative effect on the llvm benchmarks.
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static const unsigned AliasedCheckLimit = 10;
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/// \returns the parent basic block if all of the instructions in \p VL
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/// \returns the parent basic block if all of the instructions in \p VL
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/// are in the same block or null otherwise.
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/// are in the same block or null otherwise.
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static BasicBlock *getSameBlock(ArrayRef<Value *> VL) {
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static BasicBlock *getSameBlock(ArrayRef<Value *> VL) {
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@ -2754,11 +2758,22 @@ void BoUpSLP::BlockScheduling::calculateDependencies(ScheduleData *SD,
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Instruction *SrcInst = BundleMember->Inst;
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Instruction *SrcInst = BundleMember->Inst;
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AliasAnalysis::Location SrcLoc = getLocation(SrcInst, SLP->AA);
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AliasAnalysis::Location SrcLoc = getLocation(SrcInst, SLP->AA);
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bool SrcMayWrite = BundleMember->Inst->mayWriteToMemory();
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bool SrcMayWrite = BundleMember->Inst->mayWriteToMemory();
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unsigned numAliased = 0;
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while (DepDest) {
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while (DepDest) {
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assert(isInSchedulingRegion(DepDest));
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assert(isInSchedulingRegion(DepDest));
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if (SrcMayWrite || DepDest->Inst->mayWriteToMemory()) {
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if (SrcMayWrite || DepDest->Inst->mayWriteToMemory()) {
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if (SLP->isAliased(SrcLoc, SrcInst, DepDest->Inst)) {
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// Limit the number of alias checks, becaus SLP->isAliased() is
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// the expensive part in the following loop.
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if (numAliased >= AliasedCheckLimit
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|| SLP->isAliased(SrcLoc, SrcInst, DepDest->Inst)) {
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// We increment the counter only if the locations are aliased
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// (instead of counting all alias checks). This gives a better
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// balance between reduced runtime accurate dependencies.
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numAliased++;
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DepDest->MemoryDependencies.push_back(BundleMember);
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DepDest->MemoryDependencies.push_back(BundleMember);
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BundleMember->Dependencies++;
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BundleMember->Dependencies++;
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ScheduleData *DestBundle = DepDest->FirstInBundle;
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ScheduleData *DestBundle = DepDest->FirstInBundle;
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