On Tue, Mar 4, 2008 at 7:58 PM, Diego Novillo <[EMAIL PROTECTED]> wrote: > Both PHIs and birthpoints are merely factoring devices that let you cut > down the number of UD links. They don't need to be part of the IL, much > like none of the DF objects are part of the RTL IL.
Maybe they don't need to be, but it may be useful to have them anyway. > > What about keeping things up-to-date after applying some > > transformations? It is already hard to keep UD/DU chains up-to-date > > now (I don't think any pass successfully does so right now). This > > should be a lot easier if you fully factorize your UD chains, right? > > In theory, yes. Code for keeping these things up-to-date already exists > in GIMPLE SSA. That code is IMHO just awfully ugly. And slow too, last I checked. I don't know if this is still true, but update_ssa used to walk a huge part of the dominator tree even for seemingly trivial updates. We should not want that on RTL. I don't think we should allow transformations on RTL that are too hard to manually update the FUD chains somehow. Gr. Steven
