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Re: [tree-ssa] Insert on edge comment
- From: Andrew MacLeod <amacleod at redhat dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: "Vladimir N. Makarov" <vmakarov at redhat dot com>,Michael Matz <matz at suse dot de>, gcc mailing list <gcc at gcc dot gnu dot org>
- Date: 30 May 2003 19:31:08 -0400
- Subject: Re: [tree-ssa] Insert on edge comment
- References: <200305302313.h4UNDbMO020289@speedy.slc.redhat.com>
On Fri, 2003-05-30 at 19:13, law@redhat.com wrote:
> In message <3ED7E4C7.69416EBC@redhat.com>, "Vladimir N. Makarov" writes:
> >I am ignorant too (never looked at ssa-tree branch). As I understand the
> >problem is in phi nodes which are based on dominator frontier analysis.
> >Insertion of new BB is simple for general IR but for SSA it can significantly
> >change dominator frontiers for many blocks and as consequence phi-nodes in
> >the dominator frontiers. So updating phi-nodes is not a trivial task.
> That's certainly true as well. If you look at how we do this at the
> RTL level, you'll find that we don't split edges while in SSA form.
> Instead we queue things (such as edge insertions) and split the edge
> after we no longer need dominance info and PHI nodes.
>
PRE will probably want to insert things on edge and commit them before
we are done with PHI nodes :-) I suspect I'll need to add PHI node
updating as a flag to the commit routine.
Andrew