RFC: define_predicate

[Joern Rennecke]

> if genpreds.c would put an additional switch statement before the user 
> code.  Well, maybe in this case it is not that much more readable (maybe 
> the opposite is true), but in many predicates the third argument to 
> define_predicate would be superfluous, as in
> 
> +;; Return 1 if OP refers to a symbol.
> +(define_predicate "symbolic_operand" "symbol_ref,const,label_ref"
> +{
> +  switch (GET_CODE (op))
> +    {
> +    case CONST:
> +    case SYMBOL_REF:
> +    case LABEL_REF:
> +      return 1;
> +
> +    default:
> +      break;
> +    }
> +  return 0;
> +})
> 
> and that argument could be made optional (defaulting to "return 1;"). 
> Does this make sense?

It's very hard to optimize that switch statement away if it is not needed.
I propose it is only inserted if you omit the third argument.

For are worried about people shooting themselves in the foot, for
ENABLE_CHECKING, you could create wrappers that check that there are
no positives that disagree with the rtx_code.