Re: gcc 3.5 integration branch proposal

[Jan Hubicka <hubicka at ucw dot cz>]

> In fact, I finally got around to building gcc-head, and comparing it
> to gcc 3.3.2.
> 
> To say that the results are disappointing would be an understatement:
> 
> Time for a kernel compile, gcc 3.3.2:
>   276.63s real   193.01s user    26.86s system
> with gcc-head:
>   341.31s real   213.25s user    27.87s system
> 
> Exact same options, basically -O2.
> 
> Now, tell me again that GCC is getting faster...

This is precisely what I intend to do now, yes.
I re-did your experiment on my notebook (Centrino, 256MB ram) with Linux
kernel 2.6.1.  I disabled checking and profiledbootstrapped mainline, 
and compared it to current disabled checking bootstrapped 3.2 branch.

For 3.4 I get:
real    6m44.513s
user    6m13.057s
sys     0m23.915s

For 3.2 I get:
real    7m53.661s
user    7m19.730s
sys     0m24.206s

A 17% speedup (I re-did the 3.2 test 3 times with ~10 second
fluctulation).  Compare it to difference in between 2.95 and 3.2 and I
think you can clearly notice that speed issues are improving, tought the
progress is not as fast as we all would wish.  Additionally I get 250Kb
savings on 5MB vmlinux binary.

I just noticed that you did used 3.3 instead of 3.2.  I will re-do with
3.3 tree, but it is unlikely I will find it another 23% faster, but I
will give it a try.

Of course this is not claiming that it is impossible to find situation
where GCC performs like you reported.  So in order to solve your
problem, you need to be more specific about your environment and provide
either a profiles or a way to reproduce it for us.
In the case you do worry about performance of GCC, you can do a lot even
without active development of GCC.  The existence of CSiBE benchmark and
Gerald's testcase itself made the situation a lot better compilation
time wise, similarly as existence of SPEC testing machines did to the
performance

I am attaching oprofiles in the case someone will find them interesting.

Honza

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