[PING] fwprop in 4.3 stage 1?

[Steven Bosscher]

On 10/31/06, Roger Sayle <roger@eyesopen.com> wrote:
> I foresee no problems in getting the fwprop pass merged into mainline
> this week.  One detail I would like resolved however, is if you and
> Steven Bosscher could confirm you're both co-ordinating your efforts.
> Presumably, adding fwprop is part of the agreed upon game-plan, and
> not something that will complicate Steven's CSE efforts.

We're not co-ordinating the effort right now, but we've obviously been
working very hard together in GCC 4.2 stage1, and fwprop was "part of
the plan" back then to eliminate CSE path following completely (a goal
that I've since abandoned).

What fwprop should achieve, is:
- catch the optimizations we miss with CSE skip-blocks disabled
- make the first gcse.c local const/copy prop pass redundant

It used to do both these things quite well late last year, and I have
no reason to believe that it would be any different right now. The
only downside is that the compile time benefit is not as big as it
would have been if CSE path following could have been eliminated, but
fwprop is really fast anyway.

Also, fwprop is a nice example pass for how to use df.c and how to use
the CFG instead of working around it like CSE does ;-)

So, having fwprop in the trunk will only be a good thing IMHO.

Gr.
Steven