[RS6000] Ignore "c", "l" and "h" for register preference

This catches a few places where move insn patterns don't slightly
disparage CTR, LR and VRSAVE regs.  Also fixes the doc for the rs6000
h constraint, and removes an r->cl alternative covered by r->h.

Segher okayed a patch adding "*" like this patch a long time ago.
Somehow I never committed it.  This one does a few more things as
well, but I think it's sufficiently obvious to commit as such.
Bootstrapped etc. powerpc64le-linux and committed rev 266044.

	* gcc/doc/md.texi (Machine Constraints): Correct rs6000 h constraint
	description.
	* config/rs6000/rs6000.md (movsi_internal1): Delete MT%0 case
	covered by alternative.
	(movcc_internal1): Ignore h for register preference.
	(mov<mode>_hardfloat64): Likewise.
	(mov<mode>_softfloat): Ignore c, l, h for register preference.

On Tue, Nov 13, 2018 at 01:35:42PM +1030, Alan Modra wrote:
> This catches a few places where move insn patterns don't slightly
> disparage CTR, LR and VRSAVE regs.  Also fixes the doc for the rs6000
> h constraint, and removes an r->cl alternative covered by r->h.
> 
> Segher okayed a patch adding "*" like this patch a long time ago.
> Somehow I never committed it.  This one does a few more things as
> well, but I think it's sufficiently obvious to commit as such.
> Bootstrapped etc. powerpc64le-linux and committed rev 266044.

Thanks.

I'd like to move to "cl" instead of "h" though :-)

vrsave is not an allocatable register (it's a fixed register).  We do
not have to handle it in the general mov patterns at all, just needs a
separate pattern just for this.

>  (define_insn "*movcc_internal1"
>    [(set (match_operand:CC 0 "nonimmediate_operand"
> -			    "=y,x,?y,y,r,r,r,r,r,*c*l,r,m")
> +			    "=y,x,?y,y,r,r,r,r, r,*c*l,r,m")
>  	(match_operand:CC 1 "general_operand"
> -			    " y,r, r,O,x,y,r,I,h,   r,m,r"))]
> +			    " y,r, r,O,x,y,r,I,*h,   r,m,r"))]

Here you see that vrsave as dest already is not supported (and doesn't
have to be, it is never generated).

Ideally "h" does not exist anymore, and "c" and "l" are mentioned nowhere
in the normal mov patterns.


Segher

On Tue, Nov 13, 2018 at 05:37:07AM -0600, Segher Boessenkool wrote:
> On Tue, Nov 13, 2018 at 01:35:42PM +1030, Alan Modra wrote:
> > This catches a few places where move insn patterns don't slightly
> > disparage CTR, LR and VRSAVE regs.  Also fixes the doc for the rs6000
> > h constraint, and removes an r->cl alternative covered by r->h.
> > 
> > Segher okayed a patch adding "*" like this patch a long time ago.
> > Somehow I never committed it.  This one does a few more things as
> > well, but I think it's sufficiently obvious to commit as such.
> > Bootstrapped etc. powerpc64le-linux and committed rev 266044.
> 
> Thanks.
> 
> I'd like to move to "cl" instead of "h" though :-)
> 
> vrsave is not an allocatable register (it's a fixed register).  We do
> not have to handle it in the general mov patterns at all, just needs a
> separate pattern just for this.

Yes, I had the same thought, but then it wouldn't have been quite such
an obvious patch, and I figure that getting there from where we are
now is not worse than before the patch I committed.

I'll write you a patch to get rid of "h" if it's less work for you to
review my patch than it is to write it yourself.  What would you like?

Morning!

On Mon, Nov 19, 2018 at 05:06:07PM +1030, Alan Modra wrote:
> On Tue, Nov 13, 2018 at 05:37:07AM -0600, Segher Boessenkool wrote:
> > On Tue, Nov 13, 2018 at 01:35:42PM +1030, Alan Modra wrote:
> > > This catches a few places where move insn patterns don't slightly
> > > disparage CTR, LR and VRSAVE regs.  Also fixes the doc for the rs6000
> > > h constraint, and removes an r->cl alternative covered by r->h.
> > > 
> > > Segher okayed a patch adding "*" like this patch a long time ago.
> > > Somehow I never committed it.  This one does a few more things as
> > > well, but I think it's sufficiently obvious to commit as such.
> > > Bootstrapped etc. powerpc64le-linux and committed rev 266044.
> > 
> > Thanks.
> > 
> > I'd like to move to "cl" instead of "h" though :-)
> > 
> > vrsave is not an allocatable register (it's a fixed register).  We do
> > not have to handle it in the general mov patterns at all, just needs a
> > separate pattern just for this.
> 
> Yes, I had the same thought, but then it wouldn't have been quite such
> an obvious patch, and I figure that getting there from where we are
> now is not worse than before the patch I committed.
> 
> I'll write you a patch to get rid of "h" if it's less work for you to
> review my patch than it is to write it yourself.  What would you like?

Oh, this patch is approved, sorry I didn't yet say that.  Thanks!

I'd like to remove "h", or at least our use of it; I'm afraid there may
still be users of it though, in asm.  Let's do it at the start of the
GCC 10 cycle?


Segher