[PATCH], Add power9 support to GCC, patch #5 (ISA 3.0 fusion)

Michael Meissner meissner@linux.vnet.ibm.com
Mon Nov 9 22:17:00 GMT 2015


On Mon, Nov 09, 2015 at 01:11:41PM -0800, David Edelsohn wrote:
> On Mon, Nov 9, 2015 at 11:57 AM, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> > On Mon, Nov 09, 2015 at 12:34:20PM -0500, Michael Meissner wrote:
> >> > > +(define_insn "*toc_fusionload_<mode>"
> >> > > +  [(set (match_operand:QHSI 0 "int_reg_operand" "=&b,??r")
> >> > > + (match_operand:QHSI 1 "toc_fusion_mem_wrapped" "wG,wG"))
> >> > > +   (unspec [(const_int 0)] UNSPEC_FUSION_ADDIS)
> >> > > +   (use (match_operand:DI 2 "base_reg_operand" "r,r"))
> >> > > +   (clobber (match_scratch:DI 3 "=X,&b"))]
> >> > > +  "TARGET_TOC_FUSION_INT"
> >> >
> >> > Do you need that "??r" alternative?  Same for the next define_insn.
> >>
> >> Yes unfortunately.  The ??r catches the case where r0 is chosen.  R0 is not a
> >> base register, and it can't be used for power8 gpr fusion (where you use the
> >> value being loaded for the ADDIS instruction), but it can be used for power9
> >> fusion (where the ADDIS must be adjancent, but it no longer has to be the
> >> register being loaded).
> >
> > If you have only "b", r0 will not be chosen.  Does that help?  Or are
> > you generating this pattern from somewhere else where you put in r0?
> 
> Mike,
> 
> What happens if you leave out the "r" alternative?  Does other code
> explicitly generate that pattern with r0?

Sometimes, one of the passes after reload (usually -fgcse-after-reload) decides
to redo the register allocation, and I would see a failure in building things
like Spec 2006.  I have tried not putting the "r" in there, or using
base_reg_operand instead of gpc_reg_operand, but I still got failures.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.vnet.ibm.com, phone: +1 (978) 899-4797



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