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Re: Gcc 3.1 performance regressions with respect to 2.95.3
- From: law at redhat dot com
- To: David Edelsohn <dje at watson dot ibm dot com>
- Cc: Michael Matz <matzmich at cs dot tu-berlin dot de>, gcc-patches at gcc dot gnu dot org
- Date: Tue, 28 May 2002 09:19:19 -0600
- Subject: Re: Gcc 3.1 performance regressions with respect to 2.95.3
- Reply-to: law at redhat dot com
I'm trying to pick up this thread and get some resolution on this issue. So
forgive me if we end up rehashing anything.
In message <200204252212.SAA22194@makai.watson.ibm.com>, David Edelsohn
writes:
> Sigh^2. The open-coded no-conflict block does not work as a
> normal no-conflict block. This algorithm probably is not strictly a word
> at a time, so no-conflict causes optimization errors down the line.
Bummer. Are we still going to need the naked clobber though? Presumably we
have it for flow's benefit?
> I guess one other question is why the target REG is re-used
> instead of a new pseudo generated. That also would prevent the DEAD notes
> from disappearing.
If you can safely use a new pseudo that would be preferable; various early
passes in the compiler try to be sensitive to the needs of 2 address
architectures (x86, m68k, etc) and sometimes re-use pseudos. However, I
think that's exposing target details far earlier than is advantageous. So
I'm all for generating a new pseudo.
jeff