Fix a bug in the over-index constant folding. When over-indexing an
array member of a struct, it's possible to land in an arbitrary position
inside that struct, such that attempting to find further getelementptr
indices will fail. In such cases, folding cannot be done.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79485 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 5fae1ea..459a188 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -165,8 +165,11 @@
// Also, this helps GlobalOpt do SROA on GlobalVariables.
const Type *Ty = Ptr->getType();
SmallVector<Constant*, 32> NewIdxs;
- for (unsigned Index = 1; Index != NumOps; ++Index) {
+ do {
if (const SequentialType *ATy = dyn_cast<SequentialType>(Ty)) {
+ // The only pointer indexing we'll do is on the first index of the GEP.
+ if (isa<PointerType>(ATy) && ATy != Ptr->getType())
+ break;
// Determine which element of the array the offset points into.
uint64_t ElemSize = TD->getTypeAllocSize(ATy->getElementType());
if (ElemSize == 0)
@@ -183,20 +186,33 @@
Offset -= SL.getElementOffset(ElIdx);
Ty = STy->getTypeAtIndex(ElIdx);
} else {
- return 0;
+ // We've reached some non-indexable type.
+ break;
}
- }
+ } while (Ty != cast<PointerType>(ResultTy)->getElementType());
+
+ // If we haven't used up the entire offset by descending the static
+ // type, then the offset is pointing into the middle of an indivisible
+ // member, so we can't simplify it.
+ if (Offset != 0)
+ return 0;
// If the base is the start of a GlobalVariable and all the array indices
// remain in their static bounds, the GEP is inbounds. We can check that
// all indices are in bounds by just checking the first index only
// because we've just normalized all the indices.
- if (isa<GlobalVariable>(Ptr) && NewIdxs[0]->isNullValue())
- return ConstantExpr::getInBoundsGetElementPtr(Ptr,
- &NewIdxs[0], NewIdxs.size());
+ Constant *C = isa<GlobalVariable>(Ptr) && NewIdxs[0]->isNullValue() ?
+ ConstantExpr::getInBoundsGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size()) :
+ ConstantExpr::getGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size());
+ assert(cast<PointerType>(C->getType())->getElementType() == Ty &&
+ "Computed GetElementPtr has unexpected type!");
- // Otherwise it may not be inbounds.
- return ConstantExpr::getGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size());
+ // If we ended up indexing a member with a type that doesn't match
+ // type type of what the original indices indexed, add a cast.
+ if (Ty != cast<PointerType>(ResultTy)->getElementType())
+ C = ConstantExpr::getBitCast(C, ResultTy);
+
+ return C;
}
/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with