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Re: IRA copy heuristics
On Thu, 2008-09-04 at 20:28 -0400, David Edelsohn wrote:
> On Thu, Sep 4, 2008 at 7:39 PM, Vladimir Makarov <vmakarov@redhat.com> wrote:
> > Meanwhile I am going to submit your second patch with an added
> > comment. The patch permits gcc to generate the same quality code as
> > before your first patch.
>
> Why?
>
> As Richard said before:
>
> "... it changes
> the heuristics _without any explanation of why this is necessary_.
> IMO, that's unacceptable for our shiny, new (and generally very nice)
> register allocator. And I think it's unacceptable even if it happens
> to fix a performance regression."
I have to agree with Richard and David here. I find it troubling that
allocation order affects performance by anything other than a small
amount due to heuristic noise. It might be in the end there is a
valid reason on why Richard's patch has a positive benefit, but until
we know why, I'd rather wait.
Peter