[PATCH] Optimize strchr (s, 0) to strlen

[Richard Biener]

On Wed, Apr 20, 2016 at 12:33 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Wed, Apr 20, 2016 at 11:44:08AM +0200, Richard Biener wrote:
>> (simplify
>>  (BUILT_IN_STRCHR @0 integer_zerop)
>>  (pointer_plus @0 (BUILT_IN_STRLEN:size_type_node @0)))
>
> I still don't like this transformation and would very much prefer to see
> using rawmemchr instead on targets that provide it, and also this is
> something that IMHO should be done in the tree-ssa-strlen.c pass together
> with the other optimizations in there.  Similarly to stpcpy, which is also
> non-standard (in POSIX, but not in C), we should just look at headers if
> rawmemchr is defined with compatible prototype.
> Also, strrchr (s, 0) should be folded to strchr (s, 0) or handled the same
> like that one.
> And, while x = strchr (s, 0) to x = rawmemchr (s, 0) is a reasonable -Os
> transformation, x = s + strlen (s) is not, it makes code usually larger
> (especially because it increases register pressure across the call).

Sure - agreed.  So with the patch

(simplify
 (BUILT_IN_STRRCHR @0 integer_zerop@1)
 (BUILT_IN_STRCHR @0 @1))

is possible at least ;)

Richard.

>         Jakub