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Re: new sign/zero extension elimination pass
- From: Paolo Bonzini <bonzini at gnu dot org>
- To: Tom de Vries <tom at codesourcery dot com>
- Cc: Eric Botcazou <ebotcazou at adacore dot com>, gcc-patches at gcc dot gnu dot org, Bernd Schmidt <bernds at codesourcery dot com>
- Date: Mon, 8 Nov 2010 23:04:19 +0100
- Subject: Re: new sign/zero extension elimination pass
- References: <4CBC698B.email@example.com> <firstname.lastname@example.org> <4CC9E7A5.email@example.com> <4CD869D9.firstname.lastname@example.org>
On Mon, Nov 8, 2010 at 22:21, Tom de Vries <email@example.com> wrote:
> I just looked into using DF_INSN_USES, and I'm not sure that using that is a
> good idea. There is a difference between using note_uses and DF_INSN_USES.
> If there is an insn
> ?(reg:SI 1)
> ?(plus:SI (reg:SI 2)
> ? ? ? ? ? (reg:SI 3)))
> the note_uses helper function will be visited with the plus expression,
> something that is used in the pass (see note_use in ee.c).
This is an interesting point, thanks.
> Furthermore, I would like to know whether there is a problem with checking in
> the pass into trunk in its current form. My understanding of the discussion up
> until now is that the consensus is that the pass is useful, but not fully efficient.
> I agree with the fact that it's possible to improve it, but I also think that
> the runtime is negligible (it's an O(n) pass currently) and the benefit of
> improving the pass will not be worth the effort. I will try to confirm this with
> a profiling run on spec2000. If the profiling run confirms that the runtime is
> negligible, is the pass (in principle) ok for trunk?
I am not an RTL reviewer, so my opinion doesn't weigh too much.