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Re: [tree-ssa] Speed up tree-ssa-ccp
- From: law at redhat dot com
- To: Diego Novillo <dnovillo at redhat dot com>
- Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 16 Jun 2003 09:20:53 -0600
- Subject: Re: [tree-ssa] Speed up tree-ssa-ccp
- Reply-to: law at redhat dot com
In message <1055776018.3322.69.camel@frodo.toronto.redhat.com>, Diego Novillo w
rites:
>Cool. I was working along similar lines, but also included regular
>statements in the check.
I'd expect the gains to be much smaller for regular statements because
they can only be evaluated a set number of times (bounded by the number
of real operands associated with the statement).
PHI nodes are different in that they can be evaluated many times (once for
each incoming edge to the block). While most of the time blocks only have
a few incoming edges, EH and other odd flow control beasts (like computed
gotos) can break that assumption and make reevaluation of PHIs expensive.
But if it's showing good results above and beyond PHIs, then go for it.
>that we don't visit them again if their value has been proven VARYING or
>if they are just not interesting for CCP (i.e., they produce no value).
>The patch covers the check that you made here. Would you mind if I
>changed this test slightly?
Go right ahead.
jeff