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Re: new sign/zero extension elimination pass

On Mon, Nov 8, 2010 at 22:21, Tom de Vries <> 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
> ...
> (set
> ?(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.


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