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[IR] Extract method to get single GEP index from offset (NFC) 

This exposes the core logic of getGEPIndicesForOffset() as a
getGEPIndexForOffset() method that only returns a single offset,
instead of following the whole chain.
This commit is contained in:
Nikita Popov 2021-12-10 12:32:05 +01:00
parent 78ff12da11
commit 1d1e29ba6c
2 changed files with 47 additions and 38 deletions
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6
llvm/include/llvm/IR/DataLayout.h
View File

@ -591,6 +591,12 @@ public:
/// the result element type and Offset to be the residual offset.
SmallVector<APInt> getGEPIndicesForOffset(Type *&ElemTy, APInt &Offset) const;
/// Get single GEP index to access Offset inside ElemTy. Returns None if
/// index cannot be computed, e.g. because the type is not an aggregate.
/// ElemTy is updated to be the result element type and Offset to be the
/// residual offset.
Optional<APInt> getGEPIndexForOffset(Type *&ElemTy, APInt &Offset) const;
/// Returns a StructLayout object, indicating the alignment of the
/// struct, its size, and the offsets of its fields.
///

79
llvm/lib/IR/DataLayout.cpp
View File

@ -903,16 +903,14 @@ int64_t DataLayout::getIndexedOffsetInType(Type *ElemTy,
return Result;
}
static void addElementIndex(SmallVectorImpl<APInt> &Indices, TypeSize ElemSize,
APInt &Offset) {
static APInt getElementIndex(TypeSize ElemSize, APInt &Offset) {
// Skip over scalable or zero size elements. Also skip element sizes larger
// than the positive index space, because the arithmetic below may not be
// correct in that case.
unsigned BitWidth = Offset.getBitWidth();
if (ElemSize.isScalable() || ElemSize == 0 ||
!isUIntN(BitWidth - 1, ElemSize)) {
Indices.push_back(APInt::getZero(BitWidth));
return;
return APInt::getZero(BitWidth);
}
APInt Index = Offset.sdiv(ElemSize);
@ -923,47 +921,52 @@ static void addElementIndex(SmallVectorImpl<APInt> &Indices, TypeSize ElemSize,
Offset += ElemSize;
assert(Offset.isNonNegative() && "Remaining offset shouldn't be negative");
}
Indices.push_back(Index);
return Index;
}
Optional<APInt> DataLayout::getGEPIndexForOffset(Type *&ElemTy,
APInt &Offset) const {
if (auto *ArrTy = dyn_cast<ArrayType>(ElemTy)) {
ElemTy = ArrTy->getElementType();
return getElementIndex(getTypeAllocSize(ElemTy), Offset);
}
if (auto *VecTy = dyn_cast<VectorType>(ElemTy)) {
ElemTy = VecTy->getElementType();
unsigned ElemSizeInBits = getTypeSizeInBits(ElemTy).getFixedSize();
// GEPs over non-multiple of 8 size vector elements are invalid.
if (ElemSizeInBits % 8 != 0)
return None;
return getElementIndex(TypeSize::Fixed(ElemSizeInBits / 8), Offset);
}
if (auto *STy = dyn_cast<StructType>(ElemTy)) {
const StructLayout *SL = getStructLayout(STy);
uint64_t IntOffset = Offset.getZExtValue();
if (IntOffset >= SL->getSizeInBytes())
return None;
unsigned Index = SL->getElementContainingOffset(IntOffset);
Offset -= SL->getElementOffset(Index);
ElemTy = STy->getElementType(Index);
return APInt(32, Index);
}
// Non-aggregate type.
return None;
}
SmallVector<APInt> DataLayout::getGEPIndicesForOffset(Type *&ElemTy,
APInt &Offset) const {
assert(ElemTy->isSized() && "Element type must be sized");
SmallVector<APInt> Indices;
addElementIndex(Indices, getTypeAllocSize(ElemTy), Offset);
Indices.push_back(getElementIndex(getTypeAllocSize(ElemTy), Offset));
while (Offset != 0) {
if (auto *ArrTy = dyn_cast<ArrayType>(ElemTy)) {
ElemTy = ArrTy->getElementType();
addElementIndex(Indices, getTypeAllocSize(ElemTy), Offset);
continue;
}
if (auto *VecTy = dyn_cast<VectorType>(ElemTy)) {
ElemTy = VecTy->getElementType();
unsigned ElemSizeInBits = getTypeSizeInBits(ElemTy).getFixedSize();
// GEPs over non-multiple of 8 size vector elements are invalid.
if (ElemSizeInBits % 8 != 0)
break;
addElementIndex(Indices, TypeSize::Fixed(ElemSizeInBits / 8), Offset);
continue;
}
if (auto *STy = dyn_cast<StructType>(ElemTy)) {
const StructLayout *SL = getStructLayout(STy);
uint64_t IntOffset = Offset.getZExtValue();
if (IntOffset >= SL->getSizeInBytes())
break;
unsigned Index = SL->getElementContainingOffset(IntOffset);
Offset -= SL->getElementOffset(Index);
ElemTy = STy->getElementType(Index);
Indices.push_back(APInt(32, Index));
continue;
}
// Can't index into non-aggregate type.
break;
Optional<APInt> Index = getGEPIndexForOffset(ElemTy, Offset);
if (!Index)
break;
Indices.push_back(*Index);
}
return Indices;