Atomics: support __c11_* calls on _Atomic struct types.

When a struct's size is not a power of 2, the corresponding _Atomic() type is
promoted to the nearest. We already correctly handled normal C++ expressions of
this form, but direct calls to the __c11_atomic_whatever builtins ended up
performing dodgy operations on the smaller non-atomic types (e.g. memcpy too
much). Later optimisations removed this as undefined behaviour.

This patch converts EmitAtomicExpr to allocate its temporaries at the full
atomic width, sidestepping the issue.

llvm-svn: 252507

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 906ffa4fb54..20838db044c 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -199,7 +199,8 @@ public:
   //  case Expr::ChooseExprClass:
   void VisitCXXThrowExpr(const CXXThrowExpr *E) { CGF.EmitCXXThrowExpr(E); }
   void VisitAtomicExpr(AtomicExpr *E) {
-    CGF.EmitAtomicExpr(E, EnsureSlot(E->getType()).getAddress());
+    RValue Res = CGF.EmitAtomicExpr(E);
+    EmitFinalDestCopy(E->getType(), Res);
   }
 };
 }  // end anonymous namespace.