On Thursday, October 31, 2024, Jakub Jelinek <ja...@redhat.com> wrote:

> On Thu, Oct 31, 2024 at 10:15:03AM +0200, drago01 wrote:
> > On Thursday, October 31, 2024, Jakub Jelinek <ja...@redhat.com> wrote:
> >
> > > On Wed, Oct 30, 2024 at 10:46:01PM -0400, Neal Gompa wrote:
> > > > I know the idea of moving to -O3 has been briefly mentioned before in
> > > > other contexts when we've discussed uplifting the flags, but it looks
> > > > like Ubuntu is moving to -O3 for Ubuntu 25.04[1]. Is there a reason
> > > > why we shouldn't consider doing the same for Fedora Linux 42?
> > >
> > > Yes, this is a very bad idea.
> > >
> > > -O3 significantly increases code size (and the speed up gains aren't
> really
> > > guaranteed), which is highly undesirable when the vast majority of
> code in
> > > the distro isn't performance critical, the I-cache footprint is then
> more
> > > important.
>
> > Isn't instruction cache footprint already part of "performance" i.e if
> > performance is improved it shouldn't matter and vice versa, or what am I
> > missing?
>
> That is not how compilers work, ...
>

That's not what I meant sorry. I mean we shouldn't worry about size or
cache footprint, in the end what matters is performance. If we compile with
-O3 and binaries are faster it doesn't matter if the code size is larger.
Likewise if they are just bigger and perform worse or similar to -O2 it's
pointless. Or iow cache footprint and binary size are just factors that
determine performance, but not goals on their own.
-- 
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