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

Richard Osborne · Richard Osborne · commit 0af4aa9a19f8 · 2014-03-25T17:21:41.000Z
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
diff --git 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.
diff --git a/llvm/test/Transforms/InstCombine/bitcast-store.ll b/llvm/test/Transforms/InstCombine/bitcast-store.ll
@@ -3,19 +3,33 @@
 ; Instcombine should preserve metadata and alignment while
 ; folding a bitcast into a store.
 
-; CHECK: store i32 (...)** bitcast (i8** getelementptr inbounds ([5 x i8*]* @G, i64 0, i64 2) to i32 (...)**), i32 (...)*** %0, align 16, !tag !0
-
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 
 %struct.A = type { i32 (...)** }
 
 @G = external constant [5 x i8*]
 
+; CHECK-LABEL: @foo
+; CHECK: store i32 (...)** bitcast (i8** getelementptr inbounds ([5 x i8*]* @G, i64 0, i64 2) to i32 (...)**), i32 (...)*** %0, align 16, !tag !0
 define void @foo(%struct.A* %a) nounwind {
 entry:
   %0 = bitcast %struct.A* %a to i8***
   store i8** getelementptr inbounds ([5 x i8*]* @G, i64 0, i64 2), i8*** %0, align 16, !tag !0
   ret void
 }
 
+; Check instcombine doesn't try and fold the following bitcast into the store.
+; This transformation would not be safe since we would need to use addrspacecast
+; and addrspacecast is not guaranteed to be a no-op cast.
+
+; CHECK-LABEL: @bar
+; CHECK: %cast = bitcast i8** %b to i8 addrspace(1)**
+; CHECK: store i8 addrspace(1)* %a, i8 addrspace(1)** %cast
+define void @bar(i8 addrspace(1)* %a, i8** %b) nounwind {
+entry:
+  %cast = bitcast i8** %b to i8 addrspace(1)**
+  store i8 addrspace(1)* %a, i8 addrspace(1)** %cast
+  ret void
+}
+
 !0 = metadata !{metadata !"hello"}
