Re: optimization/10189: pentium4 breaks suns libm code for__ieee754_pow(double x, double y)

[Alexander Leidinger <Alexander at Leidinger dot net>]

On 26 Mar 2003 13:01:18 -0000
ljrittle at gcc dot gnu dot org wrote:

> Synopsis: pentium4 breaks suns libm code for __ieee754_pow(double x, double y)

[...]

>  FreeBSD src tree; and (c) that really cares about building FreeBSD
>  src with special CPU settings (do you guys really see enough speedup
>  to warrant this extra nightmare? ;-)

Without knowing anything about the FreeBSD related PRs in the gcc PR
database I just comment on the last part of the quoted sentence...

The official "allowed" optimization is "-O". But it is as easy as
setting 'CFLAGS=-my-special-optim' in /etc/make.conf and start "make
buildworld" in /usr/src to rebuild the userland with new optimizations.
And trust me, as long as gcc ships with a description of other
optimizations beneath "-O" there will be (clueless or smart... does it
really matter here?) people which will try those optimizations on
everything (after I managed to convince the Linux version of icc to
generate FreeBSD object files and committed a port into our ports
collection one of the first questions was "Are we are able to build the
userland/kernel with it?", and now after icc is also able to link files
without the help of gcc they ask "How much does it gain us to build the
userland/kernel with icc?", even if it isn't possible to use icc to
build the entire (or even large parts of the) kernel/userland yet). So
it isn't a matter of "does it improve things if I do it this way" or "is
it possible to do it this way", it's a matter of "how many PRs does it
generate when -march=pentium4 breaks something but other -march=pentiumX
optimizations don't"...

Thanks for your insightful mail,
Alexander.

-- 
            0 and 1. Now what could be so hard about that?

http://www.Leidinger.net                       Alexander @ Leidinger.net
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