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

[Hal Finkel via llvm-dev]

On 12/21/2016 04:40 PM, Mehdi Amini wrote:
>
>> On Dec 21, 2016, at 1:57 PM, Hal Finkel via llvm-dev 
>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>
>>
>> On 12/21/2016 03:36 PM, Sanjay Patel via llvm-dev wrote:
>>> 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).
>>
>> I'd recommend against reverting this until we understand more about 
>> the problem.
>
> I tend to agree, but I’d also like that we get better understanding 
> before 4.0 branches.
>
>> This is not a critical compile-time regression,
>
> I didn’t see in this thread a mention about how much alone this is 
> causing? The regression mentioned by Davide (20%) seems critical to me.
Maybe I misread this. I thought it was much smaller. We should 
double-check the data too. If this one commit is responsible for a 20% 
compile-time regression, that is indeed serious.

  -Hal

>
> —
> Mehdi
>
>
>> and we don't yet know the cause (it might just be enabling more 
>> down-stream transformations), or whether there have been any 
>> corresponding benefits to code side, performance, etc. It definitely 
>> looks like a pattern that we should catch.
>>
>>  -Hal
>>
>>>
>>> On Wed, Dec 21, 2016 at 12:12 PM Sean Silva <chisophugis at gmail.com 
>>> <mailto: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
>>>     <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)
>>>
>>>     -- Sean Silva
>>>
>>>
>>>
>>>
>>>         --
>>>
>>>
>>>         Davide
>>>
>>>
>>>
>>>
>>>
>>>         "There are no solved problems; there are only problems that
>>>         are more
>>>
>>>
>>>         or less solved" -- Henri Poincare
>>>
>>>
>>>
>>>         _______________________________________________
>>>
>>>
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>>>
>>>
>>>         llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>>>
>>>
>>>         http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>>
>>>
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>>
>> -- 
>> Hal Finkel
>> Lead, Compiler Technology and Programming Languages
>> Leadership Computing Facility
>> Argonne National Laboratory
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>

-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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