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Reverted r152620 - DSE: Shorten memset when a later store overwrites the start of it. There were all sorts of buildbot issues

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151621 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Pete Cooper
2012-02-28 05:06:24 +00:00
parent a116623e06
commit 9e1154cf5b
2 changed files with 2 additions and 137 deletions
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68
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -259,13 +259,6 @@ static bool isShortenable(Instruction *I) {
}
}
/// isMemset - Returns true if this instruction is an intrinsic memset
static bool isMemset(Instruction *I) {
IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
return II && II->getIntrinsicID() == Intrinsic::memset;
}
/// getStoredPointerOperand - Return the pointer that is being written to.
static Value *getStoredPointerOperand(Instruction *I) {
if (StoreInst *SI = dyn_cast<StoreInst>(I))
@ -317,17 +310,14 @@ namespace {
{
OverwriteComplete,
OverwriteEnd,
OverwriteStart,
OverwriteUnknown
};
}
/// isOverwrite - Return 'OverwriteComplete' if a store to the 'Later' location
/// completely overwrites a store to the 'Earlier' location.
/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
/// overwritten by 'Later', 'OverWriteStart' if the start of 'Earlier'
/// is completely overwritten by 'Later' or 'OverwriteUnknown' if nothing
/// can be determined
/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
/// overwritten by 'Later', or 'OverwriteUnknown' if nothing can be determined
static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
AliasAnalysis &AA,
@ -428,21 +418,6 @@ static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
LaterOff < int64_t(EarlierOff + Earlier.Size) &&
int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
return OverwriteEnd;
// The other interesting case is if the later store overwrites the end of
// the earlier store
//
// |--earlier--|
// |-- later --|
//
// In this case we may want to trim the size of earlier to avoid generating
// writes to addresses which will definitely be overwritten later
if (EarlierOff >= LaterOff &&
EarlierOff < int64_t(LaterOff + Later.Size) &&
int64_t(EarlierOff + Earlier.Size) >= int64_t(LaterOff + Later.Size)) {
LaterOff = LaterOff + Later.Size;
return OverwriteStart;
}
// Otherwise, they don't completely overlap.
return OverwriteUnknown;
@ -614,45 +589,6 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
DepIntrinsic->setLength(TrimmedLength);
MadeChange = true;
}
} else if (OR == OverwriteStart && isMemset(DepWrite)) {
// TODO: base this on the target vector size so that if the earlier
// store was too small to get vector writes anyway then its likely
// a good idea to shorten it
// Power of 2 vector writes are probably always a bad idea to optimize
// as any store/memset/memcpy is likely using vector instructions so
// shortening it to not vector size is likely to be slower
// TODO: shorten memcpy and memmove by offsetting the source address.
MemIntrinsic* DepIntrinsic = cast<MemIntrinsic>(DepWrite);
unsigned DepWriteAlign = DepIntrinsic->getAlignment();
if (llvm::isPowerOf2_64(InstWriteOffset) ||
((DepWriteAlign != 0) && InstWriteOffset % DepWriteAlign == 0)) {
DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW START: "
<< *DepWrite << "\n KILLER (offset "
<< InstWriteOffset << ", "
<< DepWriteOffset << ", "
<< DepLoc.Size << ")"
<< *Inst << '\n');
Value* DepWriteLength = DepIntrinsic->getLength();
Value* TrimmedLength = ConstantInt::get(DepWriteLength->getType(),
DepLoc.Size -
(InstWriteOffset -
DepWriteOffset));
DepIntrinsic->setLength(TrimmedLength);
const TargetData *TD = AA->getTargetData();
Type *IntPtrTy = TD->getIntPtrType(BB.getContext());
Value* Offset = ConstantInt::get(IntPtrTy,
InstWriteOffset - DepWriteOffset);
// Offset the start of the memset with a GEP. As the memset type is
// i8* a GEP will do this without needing to use ptrtoint, etc.
Value *Dest = GetElementPtrInst::Create(DepIntrinsic->getRawDest(),
Offset,
"",
DepWrite);
DepIntrinsic->setDest(Dest);
MadeChange = true;
}
}
}