[GNU] Allow a variable as an operand of _Alignof

parse.c

@@ -2005,6 +2005,7 @@ static Node *funcall(Token **rest, Token *tok) {
 //         | "sizeof" "(" type-name ")"
 //         | "sizeof" unary
 //         | "_Alignof" "(" type-name ")"
+//         | "_Alignof" unary
 //         | ident func-args?
 //         | str
 //         | num
@@ -2037,13 +2038,18 @@ static Node *primary(Token **rest, Token *tok) {
     return new_num(node->ty->size, tok);
   }
 
-  if (equal(tok, "_Alignof")) {
+  if (equal(tok, "_Alignof") && equal(tok->next, "(") && is_typename(tok->next->next)) {
-    tok = skip(tok->next, "(");
+    Type *ty = typename(&tok, tok->next->next);
-    Type *ty = typename(&tok, tok);
     *rest = skip(tok, ")");
     return new_num(ty->align, tok);
   }
 
+  if (equal(tok, "_Alignof")) {
+    Node *node = unary(rest, tok->next);
+    add_type(node);
+    return new_num(node->ty->align, tok);
+  }
+
   if (tok->kind == TK_IDENT) {
     // Function call
     if (equal(tok->next, "("))

test/alignof.c

@@ -30,6 +30,11 @@ int main() {
   ASSERT(0, (long)(char *)&g4 % 4);
   ASSERT(0, (long)(char *)&g5 % 8);
 
+  ASSERT(1, ({ char x; _Alignof(x); }));
+  ASSERT(4, ({ int x; _Alignof(x); }));
+  ASSERT(1, ({ char x; _Alignof x; }));
+  ASSERT(4, ({ int x; _Alignof x; }));
+
   printf("OK\n");
   return 0;
 }