[ssaupdate] Local dominance info

[Zdenek Dvorak]

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.

Zdenek