Uli, thanks. Sorry I misunderstood what you said the first time. I'm
currently testing this version, which I've verified fixes the bug. I'll
plan to commit the new version after testing provided neither you nor
David objects.
Thanks!
Bill
On Mon, 2014-03-03 at 17:17 +0100, Ulrich Weigand wrote:
> David Edelsohn wrote:
> > On Fri, Feb 28, 2014 at 7:11 PM, Bill Schmidt
> > <wschm...@linux.vnet.ibm.com> wrote:
> > > * config/rs6000/rs6000.c (rs6000_preferred_reload_class): Disallow
> > > PLUS rtx's from reloading into a superset of FLOAT_REGS; relax
> > > constraint on constants to only prevent them from being reloaded
> > > into a superset of FLOAT_REGS.
> >
> > This is okay with me. Uli is the best one to comment if this is the right
> > test.
>
>
> - if (CONSTANT_P (x) && reg_classes_intersect_p (rclass, FLOAT_REGS))
> + if ((CONSTANT_P (x) || GET_CODE (x) == PLUS)
> + && reg_class_subset_p (FLOAT_REGS, rclass))
> return NO_REGS;
>
> So the reg_class test change is really a no-op: given the set of classes
> defined for rs6000, rclass intersects FLOAT_REGS if and only if FLOAT_REGS
> is a subset of rclass ...
>
> This test (in either form) is probably safe, but not the best we can
> do when dealing with mixed superset classes like ALL_REGS, since we'll
> completely reject loading a constant into ALL_REGS, even though it could
> be loaded fine into a GPR.
>
> The best way seems to be to *restrict* the preferred reload class,
> but not all the way down to NO_REGS, but to the largest subclass of
> the original rclass that can actually handle constants (which might
> be GENERAL_REGS or BASE_REGS). This could be implemented by
> something along the lines of:
>
> if (CONSTANT_P (x) || GET_CODE (x) == PLUS)
> {
> if (reg_class_subset_p (GENERAL_REGS, rclass))
> return GENERAL_REGS;
> else if (reg_class_subset_p (BASE_REGS, rclass))
> return BASE_REGS;
> else
> return NO_REGS;
> }
>
> (which is similar to how we did it for s390).
>
> Bye,
> Ulrich
>
