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Re: [tree-ssa] PATCH to improve optimization at ssa rewrite time
- From: Andrew MacLeod <amacleod at redhat dot com>
- To: Daniel Berlin <dberlin at dberlin dot org>
- Cc: Jason Merrill <jason at redhat dot com>,gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: 13 May 2003 15:36:31 -0400
- Subject: Re: [tree-ssa] PATCH to improve optimization at ssa rewrite time
- References: <C411EE92-8578-11D7-901D-000A95A34564@dberlin.org>
On Tue, 2003-05-13 at 15:26, Daniel Berlin wrote:
> > This is very useful in conjunction with expression temporaries, which
> > produce a lot of redundant statements.
> Actually, as I pointed out to Diego privately, doing all these
> redundancy eliminations is really screwing up PRE.
> I've come up with tons of cases where we'd be able to eliminate the
> entire function if we didn't do these optimizations when going into SSA
> (because PRE would enable CCP to constant convert everything), but we
> are left with computations because we did.
> As soon as PRE is on by default, i'm going to be looking at switching
> off some of these into-SSA optimizations.
How much of that will be taken care of though when we start propagating
constants into the PHI nodes? Most of the (albeit somewhat few) cases
I've seen will then allow the PHI nodes to fold, and then things do
dissappear just the same.