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

[Davide Italiano via llvm-commits]

On Mon, Aug 21, 2017 at 1:00 PM, Haicheng Wu via llvm-commits
<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?

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).

Thanks,

--
Davide