[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, 5 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 7a99fc83830..6a4f65adb88 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2398,7 +2398,11 @@ ExprResult Sema::SemaAtomicOpsOverloaded(ExprResult TheCallResult,
 
   // Inspect the first argument of the atomic operation.
   Expr *Ptr = TheCall->getArg(0);
-  Ptr = DefaultFunctionArrayLvalueConversion(Ptr).get();
+  ExprResult ConvertedPtr = DefaultFunctionArrayLvalueConversion(Ptr);
+  if (ConvertedPtr.isInvalid())
+    return ExprError();
+
+  Ptr = ConvertedPtr.get();
   const PointerType *pointerType = Ptr->getType()->getAs<PointerType>();
   if (!pointerType) {
     Diag(DRE->getLocStart(), diag::err_atomic_builtin_must_be_pointer)