An alloca can be equal to an argument. It can't *alias* an alloca, but it could

be equal, since there's nothing preventing a caller from correctly predicting
the stack location of an alloca.

llvm-svn: 174119

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstSimplify/compare.ll b/llvm/test/Transforms/InstSimplify/compare.ll
index 56627b99a47..a6d7a64b914 100644
--- a/llvm/test/Transforms/InstSimplify/compare.ll
+++ b/llvm/test/Transforms/InstSimplify/compare.ll
@@ -647,3 +647,16 @@ unreachableblock:
   %Y = icmp eq i32* %X, null
   ret i1 %Y
 }
+
+; It's not valid to fold a comparison of an argument with an alloca, even though
+; that's tempting. An argument can't *alias* an alloca, however the aliasing rule
+; relies on restrictions against guessing an object's address and dereferencing.
+; There are no restrictions against guessing an object's address and comparing.
+
+define i1 @alloca_argument_compare(i64* %arg) {
+  %alloc = alloca i64
+  %cmp = icmp eq i64* %arg, %alloc
+  ret i1 %cmp
+  ; CHECK: alloca_argument_compare
+  ; CHECK: ret i1 %cmp
+}