Re: gcc 3.1 is still very slow, compared to 2.95.3

[Jan Hubicka <jh at suse dot cz>]

> On Fri, May 17, 2002 at 06:21:22PM +0200, Jan Hubicka wrote:
> > > Compiling the OpenBSD  kernel:
> > > 
> > > gcc 2.95.3 yields:
> > > make  229.16s user 20.34s system 89% cpu 4:38.64 total
> > > 
> > > gcc 3.1 yields:
> > > make CC=egcc  398.28s user 22.55s system 91% cpu 7:40.39 total
> 
> > I am sorry to say that according to the profiles, there is no single
> > place in GCC where we burn most of the CPU cycles.  The slowdown is commulative
> > result of many patches and it is clear that compile time performance has not
> > been thread seriously during GCC development (3.0 had number of other problems
> > that were addressed).  I personaly will care more the compile time performance
> > in next development and hope we will set up some periodic tester to check this
> > (this has proved to be effective at runtime perfomrance, where 3.1 is very well of).
> 
> > I would suggest using of -O1 for machines where is not enought CPU power to
> > compile in resonable times.  -O1 codes does not perform at all that bad
> > (Andreas Jaeger has measured 3% overall difference in performance at
> > http://www.suse.de/~aj/SPEC using 3.0.x compiler, currently the difference will
> > be probably bigger, but still acceptable) and compilation is considerably
> > faster.  It can be interesting to compare -O1 performance to -O2 performance
> > of gcc 2.95.  Since 3.1 is about 6% faster for SPECS, there is good chance that
> > -O1 3.1 code perofrms better than -O2 2.95 code.
> 
> There is something rotten in that kingdom.
> 
> -O1 results are worse than gcc 2.95.3 at -O2, still:
> make CC=egcc  275.17s user 20.71s system 82% cpu 5:57.44 total
> 
> if this isn't a significant regression, I don't know what is.
Still better than the -O2 result.  Would be possible to profile the
compiler cumulativly to figure out where it spends the time? On Linux
I use oprofile, but I am not aware of any such tool for BSD...

Honza