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


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.


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