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

[Xinliang David Li via llvm-commits]

There is a problem in threshold adjust code. It is speculatively bumped up
with a delta from the base value, and then for unreachable case, it is
reset to 0 (should really be set to threshold - base_threshold). Later when
the speculatively added value is subtracted again, inconsistent result may
occur (i.e., returns can be inlined for a case where early bailout happens).

David

On Tue, Feb 23, 2016 at 10:46 PM, Akira Hatanaka via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> If Cost=0 is supposed to mean inlining has zero cost, we should make sure
> Cost > 0 when the loop in InlineCost.cpp (line 1306) bails out early.
>
> On Tue, Feb 23, 2016 at 4:26 PM, Hans Wennborg <hans at chromium.org> wrote:
>
>> If Cost = 0 doesn't mean inlining the function has zero cost, that seems
>> broken.
>>
>> I think eraman knows this code. Maybe he wants to take a look?
>>
>> On Mon, Feb 22, 2016 at 9:11 PM, Akira Hatanaka via llvm-commits
>> <llvm-commits at lists.llvm.org> wrote:
>> > Hi Hans,
>> >
>> > This commit (or r252595) causes the inliner to inline functions you
>> don't
>> > want to inline (large functions) in some cases. For example, if you
>> compile
>> > the attached test case with "opt -inline", function "callee" will
>> always get
>> > inlined even after replicating the inline-asm instruction in the last
>> basic
>> > block a large number of times. This happens because the loop in
>> > CallAnalyzer::analyzeCall that visits the basic blocks of "callee"
>> breaks
>> > out when Cost exceeds Threshold, and when that happens Cost happens to
>> be 0.
>> > In this case Cost doesn't represent the true cost of the function
>> (Cost<=0
>> > doesn't mean "inlining is free").
>> >
>> > Could you take a look?
>> >
>> > 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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>> >> llvm-commits at lists.llvm.org
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>> >
>> >
>> >
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>> >
>>
>
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