[arch-general] [arch-dev-public] [signoff] gcc-4.5 toolchain rebuild

[Xavier Chantry]

On Sat, Apr 17, 2010 at 3:48 AM, Emmanuel Benisty <benisty.e at gmail.com> wrote:
> Thanks for your reply Allan.
>
> On Sat, Apr 17, 2010 at 5:30 AM, Allan McRae <allan at archlinux.org> wrote:
>> On 17/04/10 00:03, Emmanuel Benisty wrote:
>>>
>>> Just out of curiosity, what is the plan regarding this issue (quoted
>>> from the gcc changelog):
>>>
>>> On x86 targets, code containing floating-point calculations may run
>>> significantly slower when compiled with GCC 4.5 in strict C99
>>> conformance mode than they did with earlier GCC versions. This is due
>>> to stricter standard conformance of the compiler and can be avoided by
>>> using the option -fexcess-precision=fast;
>>>
>>
>> From what I understand, this requires passing -std=c99 (or equivalent) to
>> the compiler for it to use strict C99 mode.  So most software will not be
>> affected.  Of course, the maintainer of any software the does set C99 mode
>> should consider this.
>
> If it does affect only that type of code and if you recommend the
> maintainers to use this option in those cases then wouldn't it simpler
> to add it to /etc/makepkg.conf by default and thus make it a
> no-brainer for maintainers?
>

What's wrong with stricter standard conformance ? That sounds like a
good change.
How can you tell that these apps with floating-point calculations were
not actually buggy with previous versions of gcc (or with
-fexcess-precision=fast now) ?

It does not seem a very good idea to set that globally. I think that
should be done case per case, and not by maintainers, but by the
developers of the apps, who know well their code, and can make a
reasonable decision whether they want/need performance or
conformance/accuracy.
And you *need* to know how these two aspects are affected if you want
to make a reasoned and informed change, rather than a blind and
clueless one.