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
--
Dr. Ulrich Weigand
GNU/Linux compilers and toolchain
ulrich.weig...@de.ibm.com
