IRA patch: move clobbers downwards

[Bernd Schmidt]

On 07/13/2010 06:19 PM, Jeff Law wrote:

> Ideally, we'd just ignore the clobbers in the scheduler; however, that
> might be a PITA to implement.  But ISTM we ought to be able to shrink
> the clobber's lifetime in a single pass over the insns after the
> scheduler has run.

Well, that's exactly what my patch does.

Ignoring them isn't going to work, I think - where to place them depends
on the scheduling of other insns, but ideally the scheduling of other
insns won't depend on the clobbers.

> Or we could build a real pressure reduction pass using much of the
> scheduler's infrastructure.

Possibly something I have to do anyway for some of the PRs on my list.

I haven't tried if -fsched-pressure fixes this, but it seemed to help
with some other issues I've seen recently.  Can we make this the default?


Bernd