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[VNCoercion] avoid creating bitcast for zero offsets [NFCI] 

This could previously make it more complicated for ConstantFolding
later, leading to a higher likelyhood it would have to reject the
expression, even though zero seems like probably the common case here.

Differential Revision: https://reviews.llvm.org/D59730
This commit is contained in:
Jameson Nash 2019-11-06 12:00:36 -05:00
parent 19f01a4847
commit e244f86f4d
1 changed files with 17 additions and 13 deletions
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30
llvm/lib/Transforms/Utils/VNCoercion.cpp
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@ -412,12 +412,14 @@ int analyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr,
unsigned AS = Src->getType()->getPointerAddressSpace();
// Otherwise, see if we can constant fold a load from the constant with the
// offset applied as appropriate.
Src =
ConstantExpr::getBitCast(Src, Type::getInt8PtrTy(Src->getContext(), AS));
Constant *OffsetCst =
ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()), Src,
OffsetCst);
if (Offset) {
Src = ConstantExpr::getBitCast(Src,
Type::getInt8PtrTy(Src->getContext(), AS));
Constant *OffsetCst =
ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()),
Src, OffsetCst);
}
Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS));
if (ConstantFoldLoadFromConstPtr(Src, LoadTy, DL))
return Offset;
@ -587,16 +589,18 @@ T *getMemInstValueForLoadHelper(MemIntrinsic *SrcInst, unsigned Offset,
// Otherwise, this is a memcpy/memmove from a constant global.
MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
Constant *Src = cast<Constant>(MTI->getSource());
unsigned AS = Src->getType()->getPointerAddressSpace();
unsigned AS = Src->getType()->getPointerAddressSpace();
// Otherwise, see if we can constant fold a load from the constant with the
// offset applied as appropriate.
Src =
ConstantExpr::getBitCast(Src, Type::getInt8PtrTy(Src->getContext(), AS));
Constant *OffsetCst =
ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()), Src,
OffsetCst);
if (Offset) {
Src = ConstantExpr::getBitCast(Src,
Type::getInt8PtrTy(Src->getContext(), AS));
Constant *OffsetCst =
ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()),
Src, OffsetCst);
}
Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS));
return ConstantFoldLoadFromConstPtr(Src, LoadTy, DL);
}