Re: stormy16: limit SI reload regs

[Geoff Keating <geoffk at geoffk dot org>]

> X-Original-To: geoffk@foam.wonderslug.com
> Date: Wed, 30 Apr 2003 00:01:21 -0400
> From: DJ Delorie <dj@redhat.com>
> Cc: gcc-patches@gcc.gnu.org
> X-OriginalArrivalTime: 30 Apr 2003 04:00:54.0578 (UTC) FILETIME=[18ED1120:01C30ECD]
> 
> 
> > > One of our internal branches uncovered a failure (not reproducible in
> > > fsf by coincidence) in divconst-2, whereby $r7 is used as the target
> > > of an SI move, but that can't be split into two HI moves because $r8
> > > can't be used that way after the split.  Reload chose $r7 because it's
> > > in EIGHT_REGS but neglected to see if the mode required registers
> > > outside that class.  I'm not sure if that's reload's fault or not, but
> > > I did have success with the attached patch, which creates a sub-class
> > > just for pre-split SI moves.  Comments?
> > 
> > Yes, this is what you're supposed to do in cases like this.
> 
> It doesn't quite work.  The problem is that someone is checking the
> constraints more strictly between the time registers are selected for
> reload and the time the insn is split.  No matter what the register
> class, it sometimes picks the last register in the class, and fails.
> I'm trying a variant now where we set the reload preference to
> SEVEN_REGS but the constraint to EIGHT_REGS.  Hopefully it won't try
> to use $r7 anyway.

In that case, maybe it'd be a good idea to just fix register allocation?

-- 
- Geoffrey Keating <geoffk@geoffk.org>