[llvm-dev] llvm (the middle-end) is getting slower, December edition

Davide Italiano via llvm-dev
2016-12-18T03:48:37Z

On Dec 17, 2016 7:41 PM, "Sean Silva" <chisophugis at gmail.com>
wrote:



On Sat, Dec 17, 2016 at 6:32 PM, Davide Italiano via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Sat, Dec 17, 2016 at 1:35 PM, Davide Italiano <davide at
freebsd.org>
> wrote:
> [...]
>
> > I don't have an infrastructure to measure the runtime performance
> > benefits/regression of clang, but I have for `game7`.
> > I wasn't able to notice any fundamental speedup (at least, not
> > something that justifies a 2x build-time).
> >
>
> Just to provide numbers (using Sean's Mathematica template, thanks),
> here's a plot of the CDF of the frames in a particular level/scene.
> The curves pretty much match, and the picture in the middle shows a
> relative difference of 0.4% between Jun and Dec (which could be very
> possibly be in the noise).
>

With 5-10 runs per binary you should be able to reliably measure down to
0.5% difference on game7 (50 usec difference per frame). With just one run
per binary like you have here I would not trust a 0.4% difference.


Yeah, I agree. This was mostly a sanity check to understand if there was a
significant improvement at runtime. I ran the same test 7 times in the last
our but the difference is always in the noise, FWIW.


-- Sean Silva


> On the same scene, the difference between -O3 and -flto is 12%, FWIW.
> So it seems that at least for this particular case all the compile
> time didn't buy any runtime improvement.
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare
>
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