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reimplement GetPointerBaseWithConstantOffset().

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The new code is an improved copy of the code I deleted from Analysis/Loads.cpp.
One less compute-constant-gep-offset implementation. yay :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171326 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nuno Lopes 2012-12-31 20:48:35 +00:00
parent 0a9ff4cab3
commit 5cec34754d
1 changed files with 20 additions and 30 deletions
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50
lib/Analysis/ValueTracking.cpp
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@ -1672,40 +1672,30 @@ Value *llvm::FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range,
/// base and offset to the caller.
Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
const DataLayout &TD) {
Operator *PtrOp = dyn_cast<Operator>(Ptr);
if (PtrOp == 0 || Ptr->getType()->isVectorTy())
return Ptr;
unsigned BitWidth = TD.getPointerSizeInBits();
APInt ByteOffset(BitWidth, 0);
while (1) {
if (Ptr->getType()->isVectorTy())
break;
// Just look through bitcasts.
if (PtrOp->getOpcode() == Instruction::BitCast)
return GetPointerBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
// If this is a GEP with constant indices, we can look through it.
GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
gep_type_iterator GTI = gep_type_begin(GEP);
for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
++I, ++GTI) {
ConstantInt *OpC = cast<ConstantInt>(*I);
if (OpC->isZero()) continue;
// Handle a struct and array indices which add their offset to the pointer.
if (StructType *STy = dyn_cast<StructType>(*GTI)) {
Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
APInt GEPOffset(BitWidth, 0);
if (!GEP->accumulateConstantOffset(TD, GEPOffset))
break;
ByteOffset += GEPOffset;
Ptr = GEP->getPointerOperand();
} else if (Operator::getOpcode(Ptr) == Instruction::BitCast) {
Ptr = cast<Operator>(Ptr)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
if (GA->mayBeOverridden())
break;
Ptr = GA->getAliasee();
} else {
uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
Offset += OpC->getSExtValue()*Size;
break;
}
}
// Re-sign extend from the pointer size if needed to get overflow edge cases
// right.
unsigned PtrSize = TD.getPointerSizeInBits();
if (PtrSize < 64)
Offset = SignExtend64(Offset, PtrSize);
return GetPointerBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
Offset = ByteOffset.getSExtValue();
return Ptr;
}