Re: [Patch, Fortran] Use __builtin_expect in libgfortran

[Andrew Thomas Pinski <pinskia at gmail dot com>]

Sent from my iPhone

On Aug 3, 2008, at 3:36, Tobias Burnus <tobias.burnus@physik.fu-berlin.de 
> wrote:

> This patch replaces
>
>  if (unlikely fulfilled condition)
>    runtime_error (...);
>
> by
>  if (__builtin_expect (unlikely fulfilled condition, 0))
>    runtime_error (...);
>
> to speed up the library.

If rutime_error is marked as noreturn, gcc already does this internally.
-- Pinski

> See: http://www.imodulo.com/gnu/gcc/Other-Builtins.html
>
> "The use of __builtin_expect has now two uses:
>
> - on platforms where conditional jump instructions have prediction  
> bits
>   this information can be used to set them
>
> - on all architectures it should now be possible to use
>    -freorder-blocks
>   to use the information to put the basic blocks in an order which
>   guarantees an optimal straight pass through the code for the
>   normal case."
> (quote from http://sources.redhat.com/ml/libc-hacker/2000-04/msg00129.html
> -freorder-blocks is enabled with -O2)
>
>
> I hope that I have not missed any place or wrongly marked something as
> likely/unlikely which is not.
>
>
> Build and check-gfortraned on x86-64-linux
> OK for the trunk?
>
> Tobias
> <built-expect.diff>
> <built-expect-gen.diff.gz>