[Clang][C] Fixed a bug where we reject an _Atomic qualified integer i…

…n a switch statment

We are currently rejecting an _Atomic qualified integer in a switch statment.
This fixes the issue by doing an Lvalue conversion before trying to match on the type.
Fixes #65557

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D159522

clang/docs/ReleaseNotes.rst

@@ -226,6 +226,8 @@ Bug Fixes in This Version
   an invalid conversion during method function overload resolution.
 - Fix parser crash when dealing with ill-formed objective C++ header code. Fixes
   (`#64836 <https://github.com/llvm/llvm-project/issues/64836>`_)
+- Clang now allows an ``_Atomic`` qualified integer in a switch statement. Fixes
+  (`#65557 <https://github.com/llvm/llvm-project/issues/65557>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaOverload.cpp

@@ -6302,10 +6302,12 @@ ExprResult Sema::PerformContextualImplicitConversion(
     From = result.get();
   }
 
+  // Try converting the expression to an Lvalue first, to get rid of qualifiers.
+  ExprResult Converted = DefaultLvalueConversion(From);
+  QualType T = Converted.isUsable() ? Converted.get()->getType() : QualType();
   // If the expression already has a matching type, we're golden.
-  QualType T = From->getType();
   if (Converter.match(T))
-    return DefaultLvalueConversion(From);
+    return Converted;
 
   // FIXME: Check for missing '()' if T is a function type?
 

clang/test/Sema/atomic-expr.c

@@ -216,3 +216,9 @@ void func_18(void) {
   struct T { int a; };
   (void)(_Atomic struct T)s; // expected-error {{used type 'struct T' where arithmetic or pointer type is required}}
 }
+
+// Test if we can handle an _Atomic qualified integer in a switch statement.
+void func_19(void) {
+  _Atomic int a = 0;
+  switch (a) { }
+}