On Thu, Sep 15, 2016 at 2:21 AM, Yuan, Pengfei <y...@pku.edu.cn> wrote:
>> I think the approach is reasonable though it might still have
>> interesting effects on
>> optimization for very small growth.  So for further experimenting it
>> would be nice
> Test it on SPEC CPU with FDO enabled?
>> to have a separate PARAM_EARLY_FDO_INLINING_INSNS or maybe simply
>> adjust the PARAM_EARLY_INLINING_INSNS default accordingly when FDO is
>> enabled?
> Setting PARAM_EARLY_INLINING_INSNS to 0 when FDO is enabled should be
> equivalent to my patch.

Yes.  This means it's easy to experiment with other values than zero.  Basically
early inlining is supposed to remove abstraction penalty to

 a) reduce FDO instrumentation overhead
 b) get more realistic size estimates for the inliner

a) was particularly important back in time for tramp3d, reducing
profiling runtime
1000-fold.  b) is generally important.

PARAM_EARLY_INLINING_INSNS is supposed to be a reasonable value to
get abstraction removed but IIRC we increased it quite a bit to also get more
early optimization (to get more accurate inliner estimates).

What I am saying is that reducing PARAM_EARLY_INLINING_INSNS makes
sense for FDO but reducing it to zero is probably a bit much.

Can you do your measurements with values between zero and the current
default of 14 (wow, 14 ... didn't know it's _that_ high currently ;)).
What's the
value that crosses the boundary of diminishing returns regarding to code-size
improvements for you?


> Regards,
> Yuan, Pengfei
>> I'll let Honza also double-check the condition detecting FDO (it looks
>> like we should
>> have some abstraction for that).
>> Thanks,
>> Richard.

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