Massive performance regression from switching to gcc 4.5

[Jan Hubicka]

> On 06/30/2010 02:26 PM, Basile Starynkevitch wrote:
>> On Wed, 2010-06-30 at 14:23 -0700, Taras Glek wrote:
>>    
>>> I tried 4.5 -O2 and it's actually faster than 4.3 -Os.
>>>
>>> I am happy that -O2 performance is actually pretty good, but -Os
>>> regression is going to hurt on mobile.
>>>      
>> Did you try gcc-4.5 -flto -Os or gcc-4.5 -flto -O2?
>>
>> It would be interesting to hear that GCC is able to LTO a program as big
>> as Mozilla! And figures (notably RAM, CPU time, wallclock time for
>> build) would be interesting.
>>    
>
> Both whopr and flto cause gcc to segfault while building Mozilla.

4.5 WHOPR is completely broken.  LTO is in better shape but I am not sure if we
can resonably expect it to build mozilla.  However I would be very happy to help
getting WHOPR working for 4.6.

If you can find actual simple examples where -Os is losing size and speed we can try
to do something about them.

Honza
>
>
> Taras