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[DeadStoreElimination] Shorten beginning of memset overwritten by later stores
Summary: This change will shorten memset if the beginning of memset is overwritten by later stores. Reviewers: hfinkel, eeckstein, dberlin, mcrosier Subscribers: mgrang, mcrosier, llvm-commits Differential Revision: http://reviews.llvm.org/D18906 llvm-svn: 267197
This commit is contained in:
Jun Bum Lim
parent
fad7547388
commit
b80664f84c
@ -275,9 +275,9 @@ static bool isRemovable(Instruction *I) {
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}
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/// isShortenable - Returns true if this instruction can be safely shortened in
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/// Returns true if the end of this instruction can be safely shortened in
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/// length.
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static bool isShortenable(Instruction *I) {
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static bool isShortenableAtTheEnd(Instruction *I) {
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// Don't shorten stores for now
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if (isa<StoreInst>(I))
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return false;
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@ -288,6 +288,7 @@ static bool isShortenable(Instruction *I) {
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case Intrinsic::memset:
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case Intrinsic::memcpy:
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// Do shorten memory intrinsics.
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// FIXME: Add memmove if it's also safe to transform.
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return true;
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}
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}
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@ -297,6 +298,15 @@ static bool isShortenable(Instruction *I) {
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return false;
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}
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/// Returns true if the beginning of this instruction can be safely shortened
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/// in length.
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static bool isShortenableAtTheBeginning(Instruction *I) {
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// FIXME: Handle only memset for now. Supporting memcpy/memmove should be
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// easily done by offsetting the source address.
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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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@ -327,18 +337,19 @@ static uint64_t getPointerSize(const Value *V, const DataLayout &DL,
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}
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namespace {
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enum OverwriteResult
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{
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OverwriteComplete,
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OverwriteEnd,
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OverwriteUnknown
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};
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enum OverwriteResult {
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OverwriteBegin,
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OverwriteComplete,
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OverwriteEnd,
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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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/// Return 'OverwriteComplete' if a store to the 'Later' location completely
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/// overwrites a store to the 'Earlier' location, 'OverwriteEnd' if the end of
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/// the 'Earlier' location is completely overwritten by 'Later',
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/// 'OverwriteBegin' if the beginning of the 'Earlier' location is overwritten
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/// by 'Later', or 'OverwriteUnknown' if nothing can be determined.
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static OverwriteResult isOverwrite(const MemoryLocation &Later,
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const MemoryLocation &Earlier,
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const DataLayout &DL,
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@ -416,8 +427,8 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
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uint64_t(EarlierOff - LaterOff) + Earlier.Size <= Later.Size)
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return OverwriteComplete;
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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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// Another interesting case is if the later store overwrites the end of the
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// earlier store.
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//
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// |--earlier--|
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// |-- later --|
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@ -429,6 +440,20 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
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int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
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return OverwriteEnd;
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// Finally, we also need to check if the later store overwrites the beginning
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// of 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 move the destination address and trim the size
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// of earlier to avoid generating writes to addresses which will definitely
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// be overwritten later.
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if (LaterOff <= EarlierOff && int64_t(LaterOff + Later.Size) > EarlierOff) {
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assert (int64_t(LaterOff + Later.Size) < int64_t(EarlierOff + Earlier.Size)
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&& "Expect to be handled as OverwriteComplete" );
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return OverwriteBegin;
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}
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// Otherwise, they don't completely overlap.
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return OverwriteUnknown;
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}
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@ -603,29 +628,49 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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if (BBI != BB.begin())
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--BBI;
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break;
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} else if (OR == OverwriteEnd && isShortenable(DepWrite)) {
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} else if ((OR == OverwriteEnd && isShortenableAtTheEnd(DepWrite)) ||
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((OR == OverwriteBegin &&
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isShortenableAtTheBeginning(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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MemIntrinsic* DepIntrinsic = cast<MemIntrinsic>(DepWrite);
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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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bool IsOverwriteEnd = (OR == OverwriteEnd);
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if (!IsOverwriteEnd)
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InstWriteOffset = int64_t(InstWriteOffset + Loc.Size);
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if ((llvm::isPowerOf2_64(InstWriteOffset) &&
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DepWriteAlign <= InstWriteOffset) ||
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((DepWriteAlign != 0) && InstWriteOffset % DepWriteAlign == 0)) {
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DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW END: "
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<< *DepWrite << "\n KILLER (offset "
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<< InstWriteOffset << ", "
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<< DepLoc.Size << ")"
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<< *Inst << '\n');
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DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW "
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<< (IsOverwriteEnd ? "END" : "BEGIN") << ": "
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<< *DepWrite << "\n KILLER (offset "
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<< InstWriteOffset << ", " << 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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InstWriteOffset -
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DepWriteOffset);
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int64_t NewLength =
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IsOverwriteEnd
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? InstWriteOffset - DepWriteOffset
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: DepLoc.Size - (InstWriteOffset - DepWriteOffset);
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Value *DepWriteLength = DepIntrinsic->getLength();
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Value *TrimmedLength =
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ConstantInt::get(DepWriteLength->getType(), NewLength);
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DepIntrinsic->setLength(TrimmedLength);
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if (!IsOverwriteEnd) {
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int64_t OffsetMoved = (InstWriteOffset - DepWriteOffset);
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Value *Indices[1] = {
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ConstantInt::get(DepWriteLength->getType(), OffsetMoved)};
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GetElementPtrInst *NewDestGEP = GetElementPtrInst::CreateInBounds(
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DepIntrinsic->getRawDest(), Indices, "", DepWrite);
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DepIntrinsic->setDest(NewDestGEP);
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}
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MadeChange = true;
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}
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}
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90
test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll
Normal file
90
test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll
Normal file
@ -0,0 +1,90 @@
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; RUN: opt < %s -basicaa -dse -S | FileCheck %s
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define void @write4to7(i32* nocapture %p) {
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; CHECK-LABEL: @write4to7(
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entry:
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%arrayidx0 = getelementptr inbounds i32, i32* %p, i64 1
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%p3 = bitcast i32* %arrayidx0 to i8*
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; CHECK: [[GEP:%[0-9]+]] = getelementptr inbounds i8, i8* %p3, i64 4
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; CHECK: call void @llvm.memset.p0i8.i64(i8* [[GEP]], 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, 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 @write0to3(i32* nocapture %p) {
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; CHECK-LABEL: @write0to3(
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entry:
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%p3 = bitcast i32* %p to i8*
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; CHECK: [[GEP:%[0-9]+]] = getelementptr inbounds i8, i8* %p3, i64 4
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; CHECK: call void @llvm.memset.p0i8.i64(i8* [[GEP]], 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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store i32 1, i32* %p, align 4
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ret void
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}
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define void @write0to7(i32* nocapture %p) {
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; CHECK-LABEL: @write0to7(
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entry:
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%p3 = bitcast i32* %p to i8*
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; CHECK: [[GEP:%[0-9]+]] = getelementptr inbounds i8, i8* %p3, i64 8
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; CHECK: call void @llvm.memset.p0i8.i64(i8* [[GEP]], i8 0, i64 24, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 4, i1 false)
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%p4 = bitcast i32* %p to i64*
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store i64 1, i64* %p4, align 8
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ret void
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}
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define void @write0to7_2(i32* nocapture %p) {
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; CHECK-LABEL: @write0to7_2(
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entry:
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%arrayidx0 = getelementptr inbounds i32, i32* %p, i64 1
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%p3 = bitcast i32* %arrayidx0 to i8*
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; CHECK: [[GEP:%[0-9]+]] = getelementptr inbounds i8, i8* %p3, i64 4
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; CHECK: call void @llvm.memset.p0i8.i64(i8* [[GEP]], 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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%p4 = bitcast i32* %p to i64*
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store i64 1, i64* %p4, align 8
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ret void
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}
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; We do not trim the beginning of the eariler write if the alignment of the
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; start pointer is changed.
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define void @dontwrite0to3_align8(i32* nocapture %p) {
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; CHECK-LABEL: @dontwrite0to3_align8(
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entry:
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%p3 = bitcast i32* %p to i8*
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; CHECK: call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 8, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 8, i1 false)
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store i32 1, i32* %p, align 4
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ret void
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}
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define void @dontwrite0to1(i32* nocapture %p) {
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; CHECK-LABEL: @dontwrite0to1(
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entry:
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%p3 = bitcast i32* %p to i8*
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; CHECK: call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 4, i1 false)
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%p4 = bitcast i32* %p to i16*
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store i16 1, i16* %p4, align 4
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ret void
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}
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define void @dontwrite2to9(i32* nocapture %p) {
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; CHECK-LABEL: @dontwrite2to9(
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entry:
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%arrayidx0 = getelementptr inbounds i32, 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 32, i32 4, i1 false)
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call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 4, i1 false)
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%p4 = bitcast i32* %p to i16*
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%arrayidx2 = getelementptr inbounds i16, i16* %p4, i64 1
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%p5 = bitcast i16* %arrayidx2 to i64*
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store i64 1, i64* %p5, align 8
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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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