baby steps toward fixing some problems with inbound GEPs that overflow, as discussed 2 months ago or so.

Make sure we do not emit index computations with NSW flags so that we dont get an undef value if the GEP overflows

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160589 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 2 deletions

diff --git a/include/llvm/Transforms/Utils/Local.h b/include/llvm/Transforms/Utils/Local.h
index 84c0c58..495eab7 100644
--- a/include/llvm/Transforms/Utils/Local.h
+++ b/include/llvm/Transforms/Utils/Local.h
@@ -168,15 +168,18 @@ static inline unsigned getKnownAlignment(Value *V, const TargetData *TD = 0) {
 /// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
 /// code necessary to compute the offset from the base pointer (without adding
 /// in the base pointer).  Return the result as a signed integer of intptr size.
+/// When NoAssumptions is true, no assumptions about index computation not
+/// overflowing is made.
 template<typename IRBuilderTy>
-Value *EmitGEPOffset(IRBuilderTy *Builder, const TargetData &TD, User *GEP) {
+Value *EmitGEPOffset(IRBuilderTy *Builder, const TargetData &TD, User *GEP,
+                     bool NoAssumptions = false) {
   gep_type_iterator GTI = gep_type_begin(GEP);
   Type *IntPtrTy = TD.getIntPtrType(GEP->getContext());
   Value *Result = Constant::getNullValue(IntPtrTy);
 
   // If the GEP is inbounds, we know that none of the addressing operations will
   // overflow in an unsigned sense.
-  bool isInBounds = cast<GEPOperator>(GEP)->isInBounds();
+  bool isInBounds = cast<GEPOperator>(GEP)->isInBounds() && !NoAssumptions;
 
   // Build a mask for high order bits.
   unsigned IntPtrWidth = TD.getPointerSizeInBits();