GCC 4.0.0 Performance Regressions?
Is anybody collecting information on performance regressions in 4.0.0 (vs.
3.4.3)? I've got some results on POVRAY and BYTEmark, and BYTEmark saw some
performance regression, particularly with profiled optimization
(-fprofile-{generate,use}):
http://forums.gentoo.org/viewtopic-t-329765.html
I looked at the Bugzilla bug posting guidelines, but I don't know how to
boil this down to a tight testcase that fits those guidelines... and most of
what I saw in Bugzilla pertained to actual breakage anyway.
I'm willing to help out with this if I can get some pointers on what would
be useful to you--and if I can get the time away from my Real Work(TM) to
fiddle with this...
Jason B.
--
"My interest is in the future; I am going to spend the rest of my life
there."
-- Charles Kettering
Re: GCC 4.0.0 Performance Regressions?
On Tue, May 10, 2005 at 02:04:37AM +0200, Giovanni Bajo wrote: > You should try and isolate a single BYTEmark test which shows the biggest > regression. It's better if you manage to pack the whole test as a single > preprocessed source file. Theoretically, this file should be compilable and > linkable, and the resulting binary should run for a while doing computations. > > With this kind of help, we can analyze the regression and see why it's slower > with 4.0.0. > > Giovanni Bajo It was rather time-consuming but I managed to do it. I picked the numsort benchmark which had a serious regression: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21485 Jason B. -- "My interest is in the future; I am going to spend the rest of my life there." -- Charles Kettering
Re: GCC 4.0.0 Performance Regressions?
On Tue, May 10, 2005 at 11:46:38AM +0200, Giovanni Bajo wrote: > Jason Bucata <[EMAIL PROTECTED]> wrote: > > >> You should try and isolate a single BYTEmark test which shows the > >> biggest regression. It's better if you manage to pack the whole test > >> as a single preprocessed source file. Theoretically, this file > >> should be compilable and linkable, and the resulting binary should > >> run for a while doing computations. > >> > >> With this kind of help, we can analyze the regression and see why > >> it's slower with 4.0.0. > > > > It was rather time-consuming but I managed to do it. I picked the > > numsort benchmark which had a serious regression: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21485 > > > Many, many thanks! > > Giovanni Bajo Would it help to report some others? I might have time later this week to work on some of the others, especially now that I have a much better idea of what to look for. OTOH I don't want to bother if the fix for this regression is likely to impact the other regressions, too... unless these test cases later get turned into regression tests for the compiler test suite or something. Would it make a big difference to grab and use the latest snapshot, like the bug guidelines suggest? I'll give it a try if it really makes a big difference to the optimizer detectives, but if it doesn't help I won't waste my time. Jason B. -- "My interest is in the future; I am going to spend the rest of my life there." -- Charles Kettering
Re: GCC 4.0.0 Performance Regressions?
On Tue, May 10, 2005 at 05:52:40PM -0700, Joe Buck wrote: > On Tue, May 10, 2005 at 06:08:43PM -0500, Jason Bucata wrote: > > Would it help to report some others [regressions]? > > I might have time later this week to > > work on some of the others, especially now that I have a much better idea of > > what to look for. > > If you can find a small test with a large regression (say 30% or more), it > would be great to have a PR for such a thing. All else being equal, > smaller test cases are easier to debug, so I'd suggest starting with as > small a test as possible that causes as large a regression as possible, if > you have any like that. OK, two more bugs posted: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21507 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21527 That's it for this batch, unless somebody wants me to chase down the other problem noted in 21527. I noticed some 4.0.0 regressions in SciMark noted here: http://www.coyotegulch.com/reviews/gcc4/index.html So I've thought I might try to chase down the regressions in Sparse MIPS and LU MIPS... but that will have to wait a while while I catch up on other things. Jason B. -- "My interest is in the future; I am going to spend the rest of my life there." -- Charles Kettering
