[Sema] Fix PR28623.

In atomic builtins, we assumed that the LValue conversion on the first
argument would succeed. So, we would crash given code like:

```
void ovl(char);
void ovl(int);
__atomic_store_n(ovl, 0, 0);
```

This patch makes us not assume that said conversion is successful. :)

llvm-svn: 276232

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/test/SemaCXX/atomic-ops.cpp b/clang/test/SemaCXX/atomic-ops.cpp
new file mode 100644
index 00000000000..213161364f5
--- /dev/null
+++ b/clang/test/SemaCXX/atomic-ops.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only -triple=i686-linux-gnu -std=c++11
+
+// We crashed when we couldn't properly convert the first arg of __atomic_* to
+// an lvalue.
+void PR28623() {
+  void helper(int); // expected-note{{target}}
+  void helper(char); // expected-note{{target}}
+  __atomic_store_n(helper, 0, 0); // expected-error{{reference to overloaded function could not be resolved}}
+}