This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: IRA copy heuristics


Peter Bergner wrote:
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
Agreed. Let's at least have a reasonable explanation of why this is affecting performance so much. In theory, this kind of change ought to be in the noise.

Jeff


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]