Re: [PATCH 1/2] asm qualifiers (PR55681)

[Jason Merrill <jason@redhat.com>]

On 12/2/18 11:38 AM, Segher Boessenkool wrote:
> PR55681 observes that currently only one qualifier is allowed for
> inline asm, so that e.g. "volatile asm" is allowed, "const asm" is also
> okay (with a warning), but "const volatile asm" gives an error.  Also
> "goto" has to be last.
> 
> This patch changes things so that only "asm-qualifiers" are allowed,
> that is "volatile" and "goto", in any combination, in any order, but
> without repetitions.
> 
> 
> 2018-12-02  Segher Boessenkool  <segher@kernel.crashing.org>
> 
> 	PR inline-asm/55681
> 	* doc/extend.texi (Basic Asm): Update grammar.
> 	(Extended Asm): Update grammar.
> 
> gcc/c/
> 	PR inline-asm/55681
> 	* c-parser.c (c_parser_for_statement): Update grammar.  Allow any
> 	combination of volatile and goto, in any order, without repetitions.
> 
> gcc/cp/
> 	PR inline-asm/55681
> 	* parser.c (cp_parser_using_directive): Update grammar.  Allow any
> 	combination of volatile and goto, in any order, without repetitions.

You don't actually change cp_parser_using_directive, despite what diff 
says: you're changing cp_parser_asm_definition.

> +    for (bool done = false; !done ; )
> +      switch (cp_lexer_peek_token (parser->lexer)->keyword)
> +	{
> +	case RID_VOLATILE:
> +	  if (!volatile_p)
> +	    {
> +	      /* Remember that we saw the `volatile' keyword.  */
> +	      volatile_p = true;
> +	      /* Consume the token.  */
> +	      cp_lexer_consume_token (parser->lexer);
> +	    }
> +	  else
> +	    done = true;
> +	  break;
> +	case RID_GOTO:
> +	  if (!goto_p && parser->in_function_body)
> +	    {
> +	      /* Remember that we saw the `goto' keyword.  */
> +	      goto_p = true;
> +	      /* Consume the token.  */
> +	      cp_lexer_consume_token (parser->lexer);
> +	    }
> +	  else
> +	    done = true;
> +	  break;
> +	default:
> +	  done = true;
> +	}

An arguably simpler alternative to using the 'done' variable would be to 
'break' out of the loop after the switch, and have the consume_token 
cases explicitly 'continue'.

We also might remember the old tokens and give a more helpful error 
message in the case of duplicate keywords.

But I won't insist on either of these, the C++ changes are OK as-is.

Jason