Gcc builtin review: memchr, memrchr, rawmemchr

[OndÅej BÃlka <neleai at seznam dot cz>]

Gcc doesn't do any optimizations with these but misses several.

I already submitted that rawmemchr (s, 0) is silly, you should use
s + strlen (s) as strlen is better optimized (AFAIR around 50% faster
than rawmemchr)

Then gcc also doesn't optimize memchr with n small constant which is
possible but bit obscure. I could get similar performance improvement as
strcmp question is if its worth mainatainence. But fell free to add gcc
optimization for that.

Another use case is how wordexp abuses strchr/memchr to test membership
in set. For example it checked whitespace with

if (strchr (" \t\r\n", c))

While this would be relatively easy to implement with header and would
be candidate for ufunc calculating table in gcc would be really ugly
hack.