[InstCombine] don't assume 'inbounds' for bitcast pointer to GEP transform (PR43501)
https://bugs.llvm.org/show_bug.cgi?id=43501
We can't declare a GEP 'inbounds' in general. But we may salvage that information if
we have known dereferenceable bytes on the source pointer.
Differential Revision: https://reviews.llvm.org/D68244
llvm-svn: 373847
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 74c6980..c58e63d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2338,8 +2338,15 @@
// If we found a path from the src to dest, create the getelementptr now.
if (SrcElTy == DstElTy) {
SmallVector<Value *, 8> Idxs(NumZeros + 1, Builder.getInt32(0));
- return GetElementPtrInst::CreateInBounds(SrcPTy->getElementType(), Src,
- Idxs);
+ GetElementPtrInst *GEP =
+ GetElementPtrInst::Create(SrcPTy->getElementType(), Src, Idxs);
+
+ // If the source pointer is dereferenceable, then assume it points to an
+ // allocated object and apply "inbounds" to the GEP.
+ bool CanBeNull;
+ if (Src->getPointerDereferenceableBytes(DL, CanBeNull))
+ GEP->setIsInBounds();
+ return GEP;
}
}