[llvm] r259915 - CallAnalyzer::analyzeCall: change the condition back to "Cost < Threshold"

[Hans Wennborg via llvm-commits]

Yes, this change only reverts 2), and that did fix the size regression.

I don't have any binaries to compare, unfortunately, but since the
only thing my change did was to effectively move the threshold by 1,
the only explanation I can think off is that some number of functions
were on the threshold and this affected the inlining decision.

The significant size increase I saw was 150 KB (on a ~50 MB binary).
What's the typical range of Cost and Threshold?

On Wed, Feb 24, 2016 at 4:19 PM, Easwaran Raman via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> I'm curious about the cause of the size regression. The effect of  r252595
> is two-fold:
>
> 1. Inline zero-cost callees even if the threshold is negative or 0.
> 2. Inline positive-cost callees when they equal to the threshold (as opposed
> to less than the threshold).
>
> This change only reverts the effect  2 above. If that fixes the size
> regression, is it the case that a lot of callees had cost equal to threshold
> and the inlining decision got reversed? That could happen of course, but I
> doubt that should cause a significant regression. I suspect there are other
> subtle bugs in the code, so looking at specific instances will be useful.
>
> - Easwaran
>
>
> On Fri, Feb 5, 2016 at 12:32 PM, Hans Wennborg via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: hans
>> Date: Fri Feb  5 14:32:42 2016
>> New Revision: 259915
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=259915&view=rev
>> Log:
>> CallAnalyzer::analyzeCall: change the condition back to "Cost < Threshold"
>>
>> In r252595, I inadvertently changed the condition to "Cost <= Threshold",
>> which caused a significant size regression in Chrome. This commit
>> rectifies
>> that.
>>
>> Modified:
>>     llvm/trunk/lib/Analysis/InlineCost.cpp
>>
>> Modified: llvm/trunk/lib/Analysis/InlineCost.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InlineCost.cpp?rev=259915&r1=259914&r2=259915&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Analysis/InlineCost.cpp (original)
>> +++ llvm/trunk/lib/Analysis/InlineCost.cpp Fri Feb  5 14:32:42 2016
>> @@ -1392,7 +1392,7 @@ bool CallAnalyzer::analyzeCall(CallSite
>>    else if (NumVectorInstructions <= NumInstructions / 2)
>>      Threshold -= (FiftyPercentVectorBonus - TenPercentVectorBonus);
>>
>> -  return Cost <= std::max(0, Threshold);
>> +  return Cost < std::max(1, Threshold);
>>  }
>>
>>  #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
>>
>>
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