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

[Akira Hatanaka via llvm-commits]

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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> >
> >
> >
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