Re: [PATCH] Speed-up def_builtin_const (ix86_valid_target_attribute)

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Mar 20, 2015 at 11:33:09AM +0100, Martin LiÅka wrote:
> @@ -30670,6 +30673,20 @@ def_builtin_const (HOST_WIDE_INT mask, const char *name,
>  static void
>  ix86_add_new_builtins (HOST_WIDE_INT isa)
>  {
> +  /* Last cached isa value.  */
> +  static HOST_WIDE_INT last_tested_isa_value = 0;
> +
> +  /* We iterate through all defined builtins just if the last tested
> +     values is different from ISA and just in case there is any intersection
> +     between ISA value and union of all possible configurations.
> +     Last condition skips iterations if ISA is changed by the change has
> +     empty intersection with defined_isa_values.  */
> +  if ((isa & defined_isa_values) == 0 || isa == last_tested_isa_value
> +       || ((isa ^ last_tested_isa_value) & defined_isa_values) == 0)
> +    return;
> +
> +  last_tested_isa_value = isa;

Isn't at least the isa == last_tested_isa_value test useless?
I mean, if they are equal, then (isa ^ last_tested_isa_value) is 0
and so the third test is true.

Also, given that the loop does something only for
  (ix86_builtins_isa[i].isa & isa) != 0
it means once you call ix86_add_new_builtins with some particular
bit set in the isa, it doesn't make sense to try that bit again.

So, I think it would be better:
1) rename defined_isa_values bitmask to say deferred_isa_values
   (as in, isa bits that might still enable any new builtins)
2) in def_builtin, don't or in the mask unconditionally, but only
   in the else case - when add_builtin_function is not called
3) in ix86_add_new_builtins, don't add last_tested_isa_value at all, instead
   do:
  if ((isa & deferred_isa_values) == 0)
    return;

  deferred_isa_values &= ~isa;

That way, when you actually enable all builtins (either immediately in
def_builtin because it wasn't C/C++-like FE, or because all ISAs were
enabled from the start, or because ix86_add_new_builtins has been already
called with sufficiently full bitmask), deferred_isa_values will be 0 and
you won't do anything in the function any more.

	Jakub