Re: [PATCH][RFC] Make expansion of balanced binary trees of switches on tree level.

[Jan Hubicka <hubicka at ucw dot cz>]

> On 08/02/2017 01:51 PM, Richard Biener wrote:
> > On Wed, Aug 2, 2017 at 1:20 PM, Martin Liška <mliska@suse.cz> wrote:
> >> Hello.
> >>
> >> After some discussions with Honza, I've decided to convert current code in stmt.c that
> >> is responsible for switch expansion. More precisely, I would like to convert the code
> >> to expand gswitch statements on tree level. Currently the newly created pass is executed
> >> at the end of tree optimizations.
> >>
> >> My plan for future is to inspire in [1] and come up with some more sophisticated switch
> >> expansions. For that I've been working on a paper where I'll summarize statistics based
> >> on what I've collected in openSUSE distribution with specially instrumented GCC. If I'll be
> >> happy I can also fit in to schedule of this year's Cauldron with a talk.
> >>
> >> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
> >>
> >> Thoughts?
> > 
> > First of all thanks.
> > 
> > I think part of switch expansion moved to switch-conversion some time ago
> > (emit_case_bit_tests).  So maybe the full lowering should be in at least
> > the same source file and it should maybe applied earlier for a subset of
> > cases (very low number of cases for example).
> 
> Yep, good idea. I'll take a look.
> 
> > 
> > Did you base the code on the RTL expansion code or did you re-write it from
> > scratch?
> 
> It's based, I've just changed the function that create CFG.

I have talked Martin to do this in first step. Switch expansion is infinitely
difficult problem and I think changing representation first and keeping the
basic algorithm is easiest way to get something done.  Algorithm will be
improved next as far as I know :)

Honza
> 
> Martin