[PATCH] rebuild frequency after vrp

[Jan Hubicka]

> On 06/02/14 14:27, Jan Hubicka wrote:
> >>On 06/02/14 12:07, Jan Hubicka wrote:
> >>>
> >>>It is one of reasions why I think it would be cool to do jump threading in
> >>>early opts, too, at least in a lightweidt form.
> >>Conceptually it's pretty easy to do during the into-ssa step.  Not
> >>sure it it'd catch the cases you care about though.
> >
> >Yep, it may be an option, too. I always had in mind Muchnick style cheap
> >DOM pass run during into-SSA or as very first cleanup to get rid of unnecesary
> >code quickly and cheaply. Our DOM is bit different beast though :).
> >Very basic jump threading may fit here - never really tought about that.
> We had all this about 10 years ago ;-)  DOM actually started its
> life a Morgan-esque bolt onto the renamer.

Yep, I know :)) But being one of first SSA passes, it envoled to be bit too
smart for what I want.

I used to have some numbers on running dom or VRP early. I suppose I can
re-test them and see how much benefits that makes.  This things are bit hard
to get - strenghtening early opts always makes inliner to increase its activity
making a mess of code size comparsions.
> 
> 
> 
> >You probably know better than me how many of threading oppurtunities are
> >"obvious" and how many are the difficult ones solved by VRP&DOM. My gut feeling
> >is that doing the obvious ones may be good enough. But I do not know.
> A huge number of them are trivially derivable by just looking at the
> PHI nodes in the current block and I've pondered many times having a
> simpler jump threading pass that runs early in the gimple pipeline.

Yep, I think it would make sense indeed even though we currently have 3 threading
passes and I am responsible for one of them already :)

Honza
> 
> Jeff