[Bug target/64580] very high rs6000_stack_info() usage during LTO Firefox build on ppc64

["trippels at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64580

--- Comment #4 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #3)
> Hi again,
> 
> Unfortunately it seems I am unable to build a version of GCC that is
> compatible with that (every version I tried either complains or ICEs).

Yes, it's unfortunate that there is no stable interface at all. Every
patch in this area potentially breaks things and there were a couple of
them in the last few days.

> Maybe you can answer the above questions yourself?  How often
> is rs6000_output_mi_thunk called (+ some sense of scale, e.g.
> how many "real" functions are emitted)?  Is there a real hotspot
> in rs6000_stack_info itself?  I haven't been able to get it above
> 0.16% of cpu time, and no hotspots.

I will try to collect some callgrind data later today.

> Can perf be used to analyze results on a different machine than
> used to generate the data?

If the version of perf is the same then yes.