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Re: [tree-ssa] Remove semi-pruned support
- From: Diego Novillo <dnovillo at redhat dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: Chris Lattner <sabre at nondot dot org>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 20 Jan 2004 11:16:24 -0500
- Subject: Re: [tree-ssa] Remove semi-pruned support
- Organization: Red Hat Canada
- References: <200401201458.i0KEwQIb003509@speedy.slc.redhat.com>
On Tue, 2004-01-20 at 09:58, law@redhat.com wrote:
> IIRC Daniel had a code snippet which might have benefited from using
> semi-pruned and I've got vague memories of seeing a mention in a paper
> that the extra PHIs were sometimes useful. I've never personally run into
> any code or transformation which was easier/better in semi-pruned form.
>
It's mentioned in Cytron's original SSA paper. Can't quite remember the
example off the top of my head.
> Beyond those, the objection from Diego and Dan to using fully pruned all the
> time was that it could hurt compile-time performance. My experiments from
> a long time showed that fully pruned all the time was a slight compile-time
> loser -- but since then Andrew made some changes to improve life analysis and
> we're completely avoiding the life computation for a large subset of the
> variables. The combination of those two improvements makes the compile time
> issue basically go away.
>
Agreed.
Diego.