add support for initializing static vars with a cast to union (gcc extension)

llvm-svn: 62261

clang/lib/Sema/SemaDecl.cpp

@@ -2228,7 +2228,14 @@ bool Sema::CheckForConstantInitializer(Expr *Init, QualType DclT) {
   // Allow block exprs at top level.
   if (Init->getType()->isBlockPointerType())
     return false;
-    
+
+  // GCC cast to union extension
+  // note: the validity of the cast expr is checked by CheckCastTypes()
+  if (CastExpr *C = dyn_cast<CastExpr>(Init)) {
+    QualType T = C->getType();
+    return T->isUnionType() && CheckForConstantInitializer(C->getSubExpr(), T);
+  }
+
   InitializerElementNotConstant(Init);
   return true;
 }

clang/test/Sema/cast-to-union.c

@@ -7,3 +7,13 @@ void test(int x) {
   f((union u)x); // expected-warning {{C99 forbids casts to union type}}
   f((union u)&x); // expected-error {{cast to union type from type 'int *' not present in union}}
 }
+
+union u w = (union u)2; // expected-warning {{C99 forbids casts to union type}}
+union u ww = (union u)1.0; // expected-error{{cast to union type from type 'double' not present in union}}
+union u x = 7; // expected-error{{incompatible type initializing 'int', expected 'union u'}}
+int i;
+union u zz = (union u)i; // expected-error{{initializer element is not a compile-time constant}}  expected-warning {{C99 forbids casts to union type}}
+
+struct s {int a, b;};
+struct s y = { 1, 5 };
+struct s z = (struct s){ 1, 5 };