[Bug c++/74762] [5/6/7 Regression] missing uninitialized warning (C++, parenthesized expr, TREE_NO_WARNING)

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=74762

--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #1)
> Looks like warn_uninit() suppresses the warning on 'i' because the
> TREE_NO_WARNING flag is set on the ARRAY_REF by the C++ FE (in
> finish_parenthesized_expr(), for an unrelated purpose).

I wonder if a quick work-around for this case in particular is to check for:

  if (TREE_CODE (expr) == MODIFY_EXPR)

like the C parser does:

          /* A parenthesized expression.  */
          location_t loc_open_paren = c_parser_peek_token (parser)->location;
          c_parser_consume_token (parser);
          expr = c_parser_expression (parser);
          if (TREE_CODE (expr.value) == MODIFY_EXPR)
            TREE_NO_WARNING (expr.value) = 1;
          if (expr.original_code != C_MAYBE_CONST_EXPR)
            expr.original_code = ERROR_MARK;
          /* Don't change EXPR.ORIGINAL_TYPE.  */
          location_t loc_close_paren = c_parser_peek_token (parser)->location;
          set_c_expr_source_range (&expr, loc_open_paren, loc_close_paren);
          c_parser_skip_until_found (parser, CPP_CLOSE_PAREN,
                                     "expected %<)%>");

Then the bug will only trigger for code such as ((lhs=rhs)), which is what
TREE_NO_WARNING is trying to avoid warning for.