[Question, C6X] Under what situations should we disable DCE in sched2?

[Julian Brown]

On Thu, 27 Mar 2014 16:02:49 +0000
Julian Brown <julian@codesourcery.com> wrote:

> On Thu, 27 Mar 2014 09:41:28 -0600
> Jeff Law <law@redhat.com> wrote:
> 
> > On 03/27/14 07:50, Felix Yang wrote:
> > > Hello,
> > >
> > >      I find DCE in sched2 is disabled for C6X backend. Is this a
> > > performance consideration? Or a GCC BUG?
> > >      And under what situations should we disable DCE in sched2?
> > >      Can anyone explain this? Many thanks.
> > In general, if a port is disabling an optimization like this, then 
> > there's something wrong with the port.
> > 
> > As to this specific issue, git/svn blame ought to point you at
> > whomever wrote this code and you can ping them directly.
> 
> IIRC, sched2 is run from md-reorg for C6X. The same trick is used by
> the ia-64 backend -- it is to avoid late passes moving instructions
> around after scheduling (breaking the arrangement of insns into
> dispatch packets). The md-reorg pass is one of the last things the
> compiler does before emitting assembly.

Oops, I missed the "DCE" part. Ignore me!

Apologies,

Julian