[llvm] r311371 - [InlineCost] Add cl::opt to allow full inline cost to be computed for debugging purposes.

[Adam Nemet via llvm-commits]

> On Aug 25, 2017, at 1:11 PM, Davide Italiano <davide at freebsd.org> wrote:
> 
> On Mon, Aug 21, 2017 at 1:00 PM, Haicheng Wu via llvm-commits
> <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
>> Author: haicheng
>> Date: Mon Aug 21 13:00:09 2017
>> New Revision: 311371
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=311371&view=rev
>> Log:
>> [InlineCost] Add cl::opt to allow full inline cost to be computed for debugging purposes.
>> 
>> Currently, the inline cost model will bail once the inline cost exceeds the
>> inline threshold in order to avoid unnecessary compile-time. However, when
>> debugging it is useful to compute the full cost, so this command line option
>> is added to override the default behavior.
>> 
>> I took over this work from Chad Rosier (mcrosier at codeaurora.org).
>> 
> 
> This causes a non-linear increase in the time spent in the inliner for
> us, even with optimization remarks disabled.
> real    0m2.889s
> vs
> real    0m30.429s
> 
> I'm under the impression the issue is that for the legacy pass manager
> we create an ORE object on-the-fly (as the inliner is a CGSCC pass,
> and ORE is a FunctionPass analysis), so ORE is always non-null and we
> compute the inlineCost in every case. For the new PM, we can rely on
> proxying, but in the current infrastructure I'm not aware of an easy
> way of obtaining function passes from outer units of IR.
> Adam/Chandler, thoughts?

Hi Davide,

Sorry about the delay.  ORE is always set irrespective of whether remarks are enabled or not regardless whether you use old or new PM.

> 
> If nothing comes up, I'm going to pass null instead of ORE in
> InlineSimple to recover from the hit (the feature will be still
> available in the new PM, where we have a much better infrastructure
> for the purpose).

I think that this interface is unfortunate conditionalizing on ORE to emit remarks.

Also the solution you used from WholeProgDevirt doesn't unfortunately work, see https://bugs.llvm.org/show_bug.cgi?id=32352 but it’s OK in the short term.

Vivek has been working on the actual solution for this to correctly define OptimizationRemarkEmitter::allowExtraAnalysis.  Vivek, do you think you can get to it soonish?  The API is currently very confusing and I’d like to do something about it.

Thanks,
Adam

> 
> Thanks,
> 
> --
> Davide

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