Re: [PATCH 4/4] ipa-cp: Select saner profile count to base heuristics on

[Martin Jambor <mjambor@suse.cz>]

Hi,

On Mon, Aug 23 2021, Martin Jambor wrote:
> When profile feedback is available, IPA-CP takes the count of the
> hottest node and then evaluates all call contexts relative to it.
> This means that typically almost no clones for specialized contexts
> are ever created because the maximum is some special function, called
> from everywhere (that is likely to get inlined anyway) and all the
> examined edges look cold compared to it.
>
> This patch changes the selection.  It simply sorts counts of all edges
> eligible for cloning in a vector and then picks the count in 90th
> percentile (the actual number is configurable via a parameter).
>
> I also tried more complex approaches which were summing the counts and
> picking the edge which together with all hotter edges accounted for a
> given portion of the total sum of all edge counts.  But first it was
> not apparently clear to me that they make more logical sense that the
> simple method and practically I always also had to ignore a few
> percent of the hottest edges with really extreme counts (looking at
> bash and python).  And when I had to do that anyway, it seemed simpler
> to just "ignore" more and take the first non-ignored count as the
> base.
>
> Nevertheless, if people think some more sophisticated method should be
> used anyway, I am willing to be persuaded.  But this patch is a clear
> improvement over the current situation.
>
> gcc/ChangeLog:
>
> 2021-08-23  Martin Jambor  <mjambor@suse.cz>
>
> 	* params.opt (param_ipa_cp_profile_count_base): New parameter.
> 	* ipa-cp.c (max_count): Replace with base_count, replace all
> 	occurrences too, unless otherwise stated.
> 	(ipcp_cloning_candidate_p): identify mostly-directly called
> 	functions based on their counts, not max_count.
> 	(compare_edge_profile_counts): New function.
> 	(ipcp_propagate_stage): Instead of setting max_count, find the
> 	appropriate edge count in a sorted vector of counts of eligible
> 	edges and make it the base_count.

Honza approved this patch in a private conversation but then I noticed I
forgot to add an entry for the new parameter into invoke.texi, so I
fixed that problem (and checked the result with make info and make pdf)
and pushed the patch to master as commit
ab1008255e37b5b51a433ed69e04c06300543799.

Thanks,

Martin