RFC: Very long alternative lists for RTL patterns like move

[Michael Meissner]

On Mon, Mar 14, 2016 at 02:55:40PM -0500, Segher Boessenkool wrote:
> On Mon, Mar 14, 2016 at 01:35:30PM -0600, Jeff Law wrote:
> > >(define_insn "mov<mode>_hardfloat"
> > >   [(set (match_operand:FMOVE32 0 "nonimmediate_operand" 
> > >   "=!r,!r,m,f,<f32_vsx>,<f32_vsx>,!r,<f32_lr>,<f32_lr2>,<f32_sm>,<f32_sm2>,<f32_av>,Z,?<f32_dm>,?r,*c*l,!r,*h")
> > >	(match_operand:FMOVE32 1 "input_operand" 
> > >	"r,m,r,f,<f32_vsx>,j,j,<f32_lm>,<f32_lm2>,<f32_sr>,<f32_sr2>,Z,<f32_av>,r,<f32_dm>,r,h,0"))]
> > >   "(gpc_reg_operand (operands[0], <MODE>mode)
> > >    || gpc_reg_operand (operands[1], <MODE>mode))
> > >    && (TARGET_HARD_FLOAT && TARGET_FPRS && TARGET_SINGLE_FLOAT)"
> 
> We can get rid of the very many different mov patterns (or at least limit
> it somewhat) by not doing a condition like this, instead using the
> "enabled" attribute?
> 
> > >The problem is you have count each alternative to get things to line up.
> > >
> > >One thing that I do when editing rs6000.md is make the columns line up 
> > >between
> > >the different operands, and then edit it with a very wide emacs screen, for
> > >example:
> 
> You can split a string over multiple lines just fine, as well.  That again
> becomes unreadable if you need too many lines, of course :-(

Yes you can split it over several lines, but that doesn't help much.

Then you have

(define_insn "mov<mode>_hardfloat"
   [(set (match_operand:FMOVE32 0 "nonimmediate_operand" "=!r,
                                                           !r,
                                                           m,
                                                           f,
                                                           <f32_vsx>,
                                                           <f32_vsx>,
                                                           !r,
                                                           <f32_lr>,
                                                           <f32_lr2>,
                                                           <f32_sm>,
                                                           <f32_sm2>,
                                                           <f32_av>,
                                                           Z,
                                                           ?<f32_dm>,
                                                           ?r,
                                                           *c*l,
                                                           !r,
                                                           *h")
	(match_operand:FMOVE32 1 "input_operand" "r,
                                                  m,
                                                  r,
                                                  f,
                                                  <f32_vsx>,
                                                  j,
                                                  j,
                                                  <f32_lm>,
                                                  <f32_lm2>,
                                                  <f32_sr>,
                                                  <f32_sr2>,
                                                  Z,
                                                  <f32_av>,
                                                  r,
                                                  <f32_dm>,
                                                  r,
                                                  h,
                                                  0"))]
   "(gpc_reg_operand (operands[0], <MODE>mode)
    || gpc_reg_operand (operands[1], <MODE>mode))
    && (TARGET_HARD_FLOAT && TARGET_FPRS && TARGET_SINGLE_FLOAT)"

...

And of course if we do add new syntax (or allow multiple moves), it will make
it harder to backport things to older releases.

-- 
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