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.
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.
Jeff
