Re: [ssaupdate] Local dominance info

[Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz>]

Hello,

> > > > this patch adds dominance information to statements, i.e. it makes it
> > > > possible to decide whether a statement precedes other one inside a basic
> > > > block without need to scan the whole block.
> > > > 
> > > > To enable this, statements inside basic block are numbered (the
> > > > numbering contains holes, so that new statements may be inserted).  This
> > > > seems to work good enough (no measurable impact on compile time).
> > > 
> > > You want to keep and maintain this information all the time?
> > 
> > yes.  Given that it costs nothing, it seems to be the best choice to me.
> > 
> > > This strikes me *much* more as a local thing that an individual pass
> > > might be interested in, and so should number the stmt's itself for the
> > > duration of its interest. 
> > 
> > Still you would need some mechanism to update things when statements are
> > inserted, so this would make things only more complicated.
> 
> and what wrong with the local_dom_insert_after() and
> local_dom_insert_before() which call the bsi routines? It looks pretty
> trivial to do that,  then the info only exists and is maintained when
> you want it.
> 
> I don't see any reason why it should be kept up to date all the time
> when virtually no-one else cares about it.

now.  I think this might be useful for SSA form updating (which is why I
comitted this to the branch), in which case it will be useful on large
number of places.

> It seems like its a cheap to
> calculate on the fly, and if its a big deal to you, then its not
> difficult to keep up to date locally if you use local dominator aware
> insert routines which call the BSI ones.

I would tend agree with your argumentation if there were any problems
(compile time or whatever) with the solution I am using now.  There is
not, so I do not see a reason why to change it to something more
complicated.

Zdenek