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Re: gcc300 vs gcc295.3 benchmarking?


Hi,

David Ronis wrote:

> While 3.0 shouldn't give worse results than 2.95.3, note that stack
> alignment only works as well as your libraries and startup modules are
> aligned.  Most installed libc's aren't, and hence, no matter how well
> 3.0 maintains alignment, chances are your code isn't aligned.

I find your observation very interesting. I learned the hard way what you
describe: http://gcc.gnu.org/ml/gcc/2001-07/msg00177.html

However, I also learned (during some investigations carried out in
collaboration with Peter Schorsch) that compiling with an appropriate
-mpreferred-stack-boundary may help, perhaps does not restore the optimal
behaviour, but helps. For instance, compiling that benchmark ("flops")
with -O2 -mpreferred-stack-boundary=2 -fomit-frame-pointer I managed to
beat VC6 :-)

Why?

Cheers,
Paolo.


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