[Haifux] GCC Conundrum

[Shlomi Fish]

On Sunday 07 June 2009 07:20:00 Ilya A. Volynets-Evenbakh wrote:
> Were results different (as in "the way one would expect") with earlier
> versions of
> gcc?
>

I didn't try. I added this compilation option recently.

Regards,

	Shlomi Fish

> Shlomi Fish wrote:
> > I'm getting strange results (and counter-intuitive ones) when trying to
> > compile a program using gcc-4.4.0-3mnb2 on Mandriva Linux Cooker.
> >
> > The program in question is:
> >
> > https://svn.berlios.de/svnroot/repos/fc-solve/trunk/fc-solve/source
> >
> > (you can checkout it using "svn co").
> >
> > And I'm getting the following benchmark timings: (in seconds)
> >
> > {{{{{{
> > dump:126.027262926102
> > dump-2:124.866523981094
> > dump-3:125.149952888489
> > dump-4:125.010930776596
> > dump-aft-reboot:127.221956968307
> > dump-flip:123.10272693634
> > dump-flip-2:121.934360027313
> > dump-flip-3:121.98522400856
> > dump-old:130.334769010544
> > dump-old-aft-reboot:122.411857128143
> > }}}}}}
> >
> > dump-old is of an old revision before I rebooted. dump-old-aft-reboot is
> > the same version after I reboot the computer.
> >
> > The dump-flip's are after doing "./Tatzer -l p4b" and then "make" (and
> > "make install") and then running:
> >
> >  ./freecell-solver-range-parallel-solve 1 32000 500 -l gi
> >
> > The dump-[234] are after doing "./Tatzer -l p4b --without-flip". What
> > this flag does is define the FCS_WITHOUT_CARD_FLIPPING macro, which in
> > turn toggles some #ifndef's in the code that eliminate a lot of code. I
> > verified that with "--without-flip" binaries are smaller.
> >
> > My question is: why is the --without-flip binaries slower than the ones
> > with the flipping logic? So far my best bet is that with the flipping
> > logic enabled (but underused) the code aligns to have fewer cache misses
> > and that it is just a co-incidence that this is the case.
> >
> > I'll appreciate any insights.
> >
> > Regards,
> >
> > 	Shlomi Fish

-- 
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Shlomi Fish       http://www.shlomifish.org/
http://www.shlomifish.org/humour/ways_to_do_it.html

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