[Bug c/116545] Support old style statement attributes

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116545

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- gcc/c/c-parser.cc.jj        2025-03-11 22:45:16.638352045 +0100
+++ gcc/c/c-parser.cc   2025-03-12 19:24:45.614217984 +0100
@@ -1820,6 +1820,7 @@ static void c_parser_objc_at_dynamic_dec
 static bool c_parser_objc_diagnose_bad_element_prefix
   (c_parser *, struct c_declspecs *);
 static location_t c_parser_parse_rtl_body (c_parser *, char *);
+static tree c_parser_handle_musttail (c_parser *, tree, attr_state &);

 #if ENABLE_ANALYZER

@@ -2519,6 +2520,26 @@ c_parser_declaration_or_fndef (c_parser
        c_finish_oacc_routine (oacc_routine_data, NULL_TREE, false);
       return result;
     }
+  else if (specs->typespec_kind == ctsk_none
+          && c_parser_next_token_is_keyword (parser, RID_RETURN))
+    {
+      attr_state astate = {};
+      specs->attrs = c_parser_handle_musttail (parser, specs->attrs, astate);
+      if (astate.musttail_p)
+       {
+         if (specs->attrs)
+           {
+             auto_urlify_attributes sentinel;
+             warning_at (c_parser_peek_token (parser)->location,
+                         OPT_Wattributes,
+                         "attribute %<musttail%> mixed with other attributes "
+                         "on %<return%> statement");
+           }
+         c_parser_statement_after_labels (parser, NULL, NULL_TREE, NULL,
+                                          astate);
+         return result;
+       }
+    }

   /* Provide better error recovery.  Note that a type name here is usually
      better diagnosed as a redeclaration.  */
@@ -8237,7 +8258,8 @@ c_parser_statement_after_labels (c_parse
        case RID_ATTRIBUTE:
          {
            /* Allow '__attribute__((fallthrough));' or
-              '__attribute__((assume(cond)));'.  */
+              '__attribute__((assume(cond)));' or
+              '__attribute__((musttail))) return'.  */
            tree attrs = c_parser_gnu_attributes (parser);
            bool has_assume = lookup_attribute ("assume", attrs);
            if (has_assume)
@@ -8252,6 +8274,20 @@ c_parser_statement_after_labels (c_parse
                    has_assume = false;
                  }
              }
+           gcc_assert (!astate.musttail_p);
+           attrs = c_parser_handle_musttail (parser, attrs, astate);
+           if (astate.musttail_p)
+             {
+               if (attrs)
+                 {
+                   auto_urlify_attributes sentinel;
+                   warning_at (c_parser_peek_token (parser)->location,
+                               OPT_Wattributes,
+                               "attribute %<musttail%> mixed with other "
+                               "attributes on %<return%> statement");
+                 }
+               goto restart;
+             }
            if (attribute_fallthrough_p (attrs))
              {
                if (c_parser_next_token_is (parser, CPP_SEMICOLON))

does that for C.