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

[Hal Finkel via llvm-dev]

On 12/21/2016 01:11 PM, Sean Silva via llvm-dev wrote:
>
>
> On Wed, Dec 21, 2016 at 8:07 AM, Davide Italiano via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>     On Mon, Dec 19, 2016 at 4:24 PM, Mikhail Zolotukhin
>     <mzolotukhin at apple.com <mailto: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)

https://llvm.org/bugs/show_bug.cgi?id=31449 - it seems that r289813 also 
is causing a miscompile.

  -Hal

>
> -- Sean Silva
>
>
>     --
>     Davide
>
>     "There are no solved problems; there are only problems that are more
>     or less solved" -- Henri Poincare
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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