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Make a couple of cleanups to the instcombine bitcast/gep

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canonicalization transform based on duncan's comments:

1) improve the comment about %.
2) within our index loop make sure the offset stays 
   within the *type size*, instead of within the *abi size*.
   This allows us to reason explicitly about landing in tail
   padding and means that issues like non-zero offsets into
   [0 x foo] types don't occur anymore.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62045 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-01-11 20:15:20 +00:00
parent 1ed86d74a8
commit dbc3bc2585
1 changed files with 13 additions and 12 deletions
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25
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -7712,7 +7712,7 @@ static bool FindElementAtOffset(const Type *Ty, int64_t Offset,
FirstIdx = Offset/TySize;
Offset %= TySize;
// Handle silly modulus not returning values [0..TySize).
// Handle hosts where % returns negative instead of values [0..TySize).
if (Offset < 0) {
--FirstIdx;
Offset += TySize;
@ -7725,12 +7725,15 @@ static bool FindElementAtOffset(const Type *Ty, int64_t Offset,
// Index into the types. If we fail, set OrigBase to null.
while (Offset) {
// Indexing into tail padding between struct/array elements.
if (uint64_t(Offset*8) >= TD->getTypeSizeInBits(Ty))
return false;
if (const StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = TD->getStructLayout(STy);
if (Offset >= (int64_t)SL->getSizeInBytes()) {
// We can't index into this, bail out.
return false;
}
assert(Offset < (int64_t)SL->getSizeInBytes() &&
"Offset must stay within the indexed type");
unsigned Elt = SL->getElementContainingOffset(Offset);
NewIndices.push_back(ConstantInt::get(Type::Int32Ty, Elt));
@ -7738,15 +7741,13 @@ static bool FindElementAtOffset(const Type *Ty, int64_t Offset,
Ty = STy->getElementType(Elt);
} else if (isa<ArrayType>(Ty) || isa<VectorType>(Ty)) {
const SequentialType *STy = cast<SequentialType>(Ty);
if (uint64_t EltSize = TD->getABITypeSize(STy->getElementType())) {
NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
Offset %= EltSize;
} else {
NewIndices.push_back(ConstantInt::get(IntPtrTy, 0));
}
uint64_t EltSize = TD->getABITypeSize(STy->getElementType());
assert(EltSize && "Cannot index into a zero-sized array");
NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
Offset %= EltSize;
Ty = STy->getElementType();
} else {
// Otherwise, we can't index into this, bail out.
// Otherwise, we can't index into the middle of this atomic type, bail.
return false;
}
}