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Re: [tree-ssa] Insert on edge comment
- From: law at redhat dot com
- To: "Vladimir N. Makarov" <vmakarov at redhat dot com>
- Cc: Michael Matz <matz at suse dot de>, Andrew MacLeod <amacleod at redhat dot com>, gcc mailing list <gcc at gcc dot gnu dot org>
- Date: Fri, 30 May 2003 17:13:37 -0600
- Subject: Re: [tree-ssa] Insert on edge comment
- Reply-to: law at redhat dot com
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.
jeff