Re: [ssaupdate] Local dominance info

[Andrew MacLeod <amacleod@redhat.com>]

On Tue, 2004-10-19 at 17:51, Zdenek Dvorak wrote:
> 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?

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. 

I think trying to keep numbered order of stmts within blocks for the
duration of SSA is a very bad idea since most optimizations do not care.
So you have the overhead of making sure that you keep things kosher
everytime you ever move anything. You will always have an end case where
the hole isnt big enough, so you'll have to renumber either the entire
block, or parts of it. This will no doubt happen during an optimization
phase that doesn't care about local numbers.

I can see having an aux field in stmts much like edges do, where an
individual pass can use that field for whatever it want, in your case
for these local dominance numbers. If you wish to maintain these numbers
for a series of optimizations and you are interested in having the
insert routines take care of it for you, then at best I could  see
creating  local_dom_insert_before(), local_dom_insert_after(), etc which
call the bsi_* insertion routines, and then update your local dominance
info. Then you could use those routine in areas where you care about it
without affecting anyone else.  This seems like it ought to be pretty
easy to do since you call setup_local_dom_number() as the last thing
after inserting.

I do not thing this should be part of the generic bsi_* routines.

Andrew