[Bug target/27077] [x86, 4.1] builtin strlen poor performance

[var at schellong dot biz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=27077

--- Comment #10 from Helmut Schellong <var at schellong dot biz> ---
(In reply to Thomas Koenig from comment #9)
> Please see https://gcc.gnu.org/bugs/#need for the things that
> are required for a bug report.
> 
> Specifically, 
> 
> the preprocessed file (*.i*) that triggers the bug, generated by adding
> -save-temps to the complete compilation command, or, in the case of a bug
> report for the GNAT front end, a complete set of source files (see below).

In this case a lot of informations are not necessary.
This can be shortened to:
   "Change each builtin that implements string instructions."
That's almost enough.

Example:
The strlen() in (my) libc reads eight bytes and realizes a zero byte
therein at a single blow.
scasb cannot be so fast (bytewise).

This C code (translated):
   while (*s)  ++s;
   return (s-s0);
runs three times faster than the scasb-builtin.
This says all-inclusive.