Re: gcc/libm floating-point bug?

On Wed, 21 May 2003 18:10:14 -0700, David O'Brien <obrien_at_FreeBSD.ORG> 
wrote:

> On Tue, May 20, 2003 at 03:12:27PM -0400, Jon Lido wrote:
>> On Tuesday 20 May 2003 02:00 pm, David Schultz wrote:
>> > On Tue, May 20, 2003, Jon Lido wrote:
>> > > Well, I do have a P4, and had built everything with -march=pentium4. 
>> > > However, rebuilding the kernel and modules with -march=pentium3 
>> produces
>> > > the same results.
>> >
>> > This isn't a kernel problem, so you need to rebuild libm and libc
>> > without -march=pentium4.  You really don't want to be using the
>> > Pentium 4 optimizations in gcc 3.2 anyway; the generated code is
>> > generally slower.  gcc 3.3 has fixes for a number of the bugs, but
>> > I don't know about the performance problems.
>>
>> Yes, this was the problem.  I rebuilt world with -march=pentium3 and 
>> that did the trick.
>
> Honest question of you -- I'll assume you're subscribed to
> freebsd-current_at_.  How have you missed all the warnings from myself and
> others not to trust the -march=pentium4 optimizations?  I honestly want
> to know so we can figure out a better way of getting the word out.

Perhaps, it should be add in the errata? Also, add the comments in the 
make.conf.

Cheers,
Mezz

>> I'm not sure how CPUTYPE gets handled, but perhaps p4 should expand to - 
>> march=pentium3, if possible.
>
> I feel some will screem if we take away the ability to use
> -march=pentium4 in places they know for sure will work.  Unix is about
> mechanisms, not policy.


-- 
bsdforums.org 's moderator, mezz.