my coalescer on ML kit: bad

[Stephen Weeks]

>                                     old coalescer           new coalescer
>         number of chunks                   11,425                   7,677
>         number of trampolines         217,944,056             206,952,722
>         number of returns             220,922,989             220,945,534
>         number of inter-chunk returns 157,022,980             103,291,304
>         number of limit checks        119,171,837             119,188,003
>         CPU time                           164.34                  165.45
> 

> The  number  of inter-chunk returns went down by 52%, which is good.  Why did
> the number of inter-chunk returns go down by  so  much  when  the  number  of
> trampolines went down hardly any?  Is it really just luck, and almost all the
> old inter-chunk calls were still inter-chunk?

It's actually worse than you say.  In order to keep the number of
trampolines up, the number of inter-chunk calls must have gone way up
(by about 45M) with the new coalescer.  I base this conclusion on the
following equation.

  trampolines = inter-chunk calls + inter-chunk returns

This may be due to some bias in the edges given as input
equivalence-graph.