[InstCombine] Don't fold bitcast into store if it would need addrspacecast

Summary:
Previously the code didn't check if the before and after types for the
store were pointers to different address spaces. This resulted in
instcombine using a bitcast to convert between pointers to different
address spaces, causing an assertion due to the invalid cast.

It is not be appropriate to use addrspacecast this case because it is
not guaranteed to be a no-op cast. Instead bail out and do not do the
transformation.

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D3117

llvm-svn: 204733

1 files changed, 16 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 4da5b51bf36..dcc8b0f84e6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -508,15 +508,27 @@ static Instruction *InstCombineStoreToCast(InstCombiner &IC, StoreInst &SI) {
   if (!SrcPTy->isIntegerTy() && !SrcPTy->isPointerTy())
     return 0;
 
-  // If the pointers point into different address spaces or if they point to
-  // values with different sizes, we can't do the transformation.
+  // If the pointers point into different address spaces don't do the
+  // transformation.
+  if (SrcTy->getAddressSpace() !=
+      cast<PointerType>(CI->getType())->getAddressSpace())
+    return 0;
+
+  // If the pointers point to values of different sizes don't do the
+  // transformation.
   if (!IC.getDataLayout() ||
-      SrcTy->getAddressSpace() !=
-        cast<PointerType>(CI->getType())->getAddressSpace() ||
       IC.getDataLayout()->getTypeSizeInBits(SrcPTy) !=
       IC.getDataLayout()->getTypeSizeInBits(DestPTy))
     return 0;
 
+  // If the pointers point to pointers to different address spaces don't do the
+  // transformation. It is not safe to introduce an addrspacecast instruction in
+  // this case since, depending on the target, addrspacecast may not be a no-op
+  // cast.
+  if (SrcPTy->isPointerTy() && DestPTy->isPointerTy() &&
+      SrcPTy->getPointerAddressSpace() != DestPTy->getPointerAddressSpace())
+    return 0;
+
   // Okay, we are casting from one integer or pointer type to another of
   // the same size.  Instead of casting the pointer before
   // the store, cast the value to be stored.