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DSE: Shorten memset when a later store overwrites the start of it
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151620 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Pete Cooper
parent
601c094734
commit
a116623e06
@ -259,6 +259,13 @@ static bool isShortenable(Instruction *I) {
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}
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}
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/// isMemset - Returns true if this instruction is an intrinsic memset
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static bool isMemset(Instruction *I) {
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IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
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return II && II->getIntrinsicID() == Intrinsic::memset;
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}
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/// getStoredPointerOperand - Return the pointer that is being written to.
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static Value *getStoredPointerOperand(Instruction *I) {
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if (StoreInst *SI = dyn_cast<StoreInst>(I))
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@ -310,14 +317,17 @@ namespace {
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{
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OverwriteComplete,
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OverwriteEnd,
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OverwriteStart,
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OverwriteUnknown
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};
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}
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/// isOverwrite - Return 'OverwriteComplete' if a store to the 'Later' location
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/// completely overwrites a store to the 'Earlier' location.
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/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
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/// overwritten by 'Later', or 'OverwriteUnknown' if nothing can be determined
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/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
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/// overwritten by 'Later', 'OverWriteStart' if the start of 'Earlier'
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/// is completely overwritten by 'Later' or 'OverwriteUnknown' if nothing
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/// can be determined
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static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
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const AliasAnalysis::Location &Earlier,
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AliasAnalysis &AA,
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@ -418,6 +428,21 @@ static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
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LaterOff < int64_t(EarlierOff + Earlier.Size) &&
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int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
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return OverwriteEnd;
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// The other interesting case is if the later store overwrites the end of
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// the earlier store
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//
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// |--earlier--|
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// |-- later --|
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//
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// In this case we may want to trim the size of earlier to avoid generating
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// writes to addresses which will definitely be overwritten later
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if (EarlierOff >= LaterOff &&
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EarlierOff < int64_t(LaterOff + Later.Size) &&
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int64_t(EarlierOff + Earlier.Size) >= int64_t(LaterOff + Later.Size)) {
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LaterOff = LaterOff + Later.Size;
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return OverwriteStart;
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}
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// Otherwise, they don't completely overlap.
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return OverwriteUnknown;
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@ -589,6 +614,45 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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DepIntrinsic->setLength(TrimmedLength);
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MadeChange = true;
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}
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} else if (OR == OverwriteStart && isMemset(DepWrite)) {
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// TODO: base this on the target vector size so that if the earlier
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// store was too small to get vector writes anyway then its likely
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// a good idea to shorten it
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// Power of 2 vector writes are probably always a bad idea to optimize
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// as any store/memset/memcpy is likely using vector instructions so
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// shortening it to not vector size is likely to be slower
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// TODO: shorten memcpy and memmove by offsetting the source address.
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MemIntrinsic* DepIntrinsic = cast<MemIntrinsic>(DepWrite);
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unsigned DepWriteAlign = DepIntrinsic->getAlignment();
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if (llvm::isPowerOf2_64(InstWriteOffset) ||
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((DepWriteAlign != 0) && InstWriteOffset % DepWriteAlign == 0)) {
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DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW START: "
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<< *DepWrite << "\n KILLER (offset "
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<< InstWriteOffset << ", "
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<< DepWriteOffset << ", "
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<< DepLoc.Size << ")"
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<< *Inst << '\n');
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Value* DepWriteLength = DepIntrinsic->getLength();
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Value* TrimmedLength = ConstantInt::get(DepWriteLength->getType(),
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DepLoc.Size -
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(InstWriteOffset -
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DepWriteOffset));
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DepIntrinsic->setLength(TrimmedLength);
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const TargetData *TD = AA->getTargetData();
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Type *IntPtrTy = TD->getIntPtrType(BB.getContext());
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Value* Offset = ConstantInt::get(IntPtrTy,
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InstWriteOffset - DepWriteOffset);
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// Offset the start of the memset with a GEP. As the memset type is
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// i8* a GEP will do this without needing to use ptrtoint, etc.
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Value *Dest = GetElementPtrInst::Create(DepIntrinsic->getRawDest(),
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Offset,
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"",
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DepWrite);
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DepIntrinsic->setDest(Dest);
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MadeChange = true;
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}
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}
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}
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71
test/Transforms/DeadStoreElimination/OverwriteStoreStart.ll
Normal file
71
test/Transforms/DeadStoreElimination/OverwriteStoreStart.ll
Normal file
@ -0,0 +1,71 @@
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; RUN: opt < %s -basicaa -dse -S | FileCheck %s
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
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%struct.vec2 = type { <4 x i32>, <4 x i32> }
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%struct.vec2plusi = type { <4 x i32>, <4 x i32>, i32 }
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@glob1 = global %struct.vec2 zeroinitializer, align 16
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@glob2 = global %struct.vec2plusi zeroinitializer, align 16
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define void @write4to8(i32* nocapture %p) nounwind uwtable ssp {
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; CHECK: @write4to8
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entry:
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%arrayidx0 = getelementptr inbounds i32* %p, i64 1
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%p3 = bitcast i32* %arrayidx0 to i8*
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; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, i8 0, i64 24, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
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%arrayidx1 = getelementptr inbounds i32* %p, i64 1
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store i32 1, i32* %arrayidx1, align 4
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ret void
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}
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define void @write4to12(i32* nocapture %p) nounwind uwtable ssp {
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; CHECK: @write4to12
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entry:
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%arrayidx0 = getelementptr inbounds i32* %p, i64 1
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%p3 = bitcast i32* %arrayidx0 to i8*
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; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, i8 0, i64 20, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
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%arrayidx1 = bitcast i32* %arrayidx0 to i64*
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store i64 1, i64* %arrayidx1, align 4
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ret void
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}
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define void @write4to8_2(i32* nocapture %p) nounwind uwtable ssp {
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; CHECK: @write4to8_2
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entry:
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%arrayidx0 = getelementptr inbounds i32* %p, i64 1
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%p3 = bitcast i32* %arrayidx0 to i8*
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; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, i8 0, i64 24, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
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%arrayidx1 = bitcast i32* %p to i64*
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store i64 1, i64* %arrayidx1, align 4
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ret void
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}
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define void @dontwrite4to6(i32* nocapture %p) nounwind uwtable ssp {
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; CHECK: @dontwrite4to6
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entry:
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%arrayidx0 = getelementptr inbounds i32* %p, i64 1
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%p3 = bitcast i32* %arrayidx0 to i8*
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; CHECK: call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
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%arrayidx1 = bitcast i32* %arrayidx0 to i16*
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store i16 1, i16* %arrayidx1, align 4
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ret void
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}
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define void @write4to8_neg_gep(i32* nocapture %p) nounwind uwtable ssp {
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; CHECK: @write4to8_neg_gep
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entry:
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%arrayidx0 = getelementptr inbounds i32* %p, i64 -1
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%p3 = bitcast i32* %arrayidx0 to i8*
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; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, i8 0, i64 24, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
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%neg2 = getelementptr inbounds i32* %p, i64 -2
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%arrayidx1 = bitcast i32* %neg2 to i64*
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store i64 1, i64* %arrayidx1, align 4
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ret void
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}
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declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
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