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

[Sanjay Patel via llvm-dev]

I would have replied to this thread sooner, but I was busy adding more
instcombines. :)

The motivation for r289855 is in the commit msg (I'm out of the office and
can't look things up conveniently). Feel free to revert that and the follow
ups, however, if that patch caused a noticeable slowdown, then it suggests
we have a bigger problem?...that's a simple matcher (no value tracking
required).

On Wed, Dec 21, 2016 at 12:12 PM Sean Silva <chisophugis at gmail.com> wrote:

> On Wed, Dec 21, 2016 at 8:07 AM, Davide Italiano via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> On Mon, Dec 19, 2016 at 4:24 PM, Mikhail Zolotukhin
>
>
> <mzolotukhin at apple.com> wrote:
>
>
> > Hi Davide,
>
>
> >
>
>
> > Thanks for the analysis, it's really interesting! And I'm really glad
> that we now put more and more attention at the compile time!
>
>
> >
>
>
> > Just recently I've been looking into historical compile time data as
> well, and have had similar conclusions. The regressions you've found are
> probably caused by:
>
>
> > 1) r289813 and r289855 - new matchers in InstCombine
>
>
> > 2) r286814 and r288024 - changes in Inlining cost model
>
>
> >
>
>
>
>
>
> Haven't looked at 2) yet, but I can confirm for 1). Sanjay/Ehsan, can
>
>
> you please explain what's the motivation behind the new
>
>
> transformations you introduced? I'm tempted to ask a revert, but I'd
>
>
> like to understand the motivations first.
>
>
>
> Both r289813 and r289855 add a very small amount of matching (it seems?)
> compared to the rest of the size of instcombine. How is it that these
> checks are causing such a disproportionate slowdown compared to the rest of
> instcombine? (by "I can confirm for 1)" I assume you mean these two patches
> have a pretty significant impact on compile time; not "0.1%" each)
>
> -- Sean Silva
>
>
>
>
>
> --
>
>
> Davide
>
>
>
>
>
> "There are no solved problems; there are only problems that are more
>
>
> or less solved" -- Henri Poincare
>
>
>
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