Compute standard conversion sequences for conversions to atomic

types. The second and third conversions in the sequence are based on
the conversion for the underlying type, so that we get sensible
overloading behavior for, e.g., _Atomic(int) vs. _Atomic(float).

As part of this, actually implement the lvalue-to-rvalue conversion
for atomic types. There is probably a pile of code in SemaExpr that
can now be deleted, but I haven't tracked it down yet.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154596 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 4 deletions

diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 7748b8c8a6..104134cdb0 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -374,10 +374,6 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   QualType T = E->getType();
   assert(!T.isNull() && "r-value conversion on typeless expression?");
 
-  // We can't do lvalue-to-rvalue on atomics yet.
-  if (T->isAtomicType())
-    return Owned(E);
-
   // We don't want to throw lvalue-to-rvalue casts on top of
   // expressions of certain types in C++.
   if (getLangOpts().CPlusPlus &&
@@ -413,6 +409,15 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   ExprResult Res = Owned(ImplicitCastExpr::Create(Context, T, CK_LValueToRValue,
                                                   E, 0, VK_RValue));
 
+  // C11 6.3.2.1p2:
+  //   ... if the lvalue has atomic type, the value has the non-atomic version 
+  //   of the type of the lvalue ...
+  if (const AtomicType *Atomic = T->getAs<AtomicType>()) {
+    T = Atomic->getValueType().getUnqualifiedType();
+    Res = Owned(ImplicitCastExpr::Create(Context, T, CK_AtomicToNonAtomic,
+                                         Res.get(), 0, VK_RValue));
+  }
+  
   return Res;
 }