Re: RFC: Using mode and code macros in *.md files

[Richard Sandiford <rsandifo at redhat dot com>]

Steve Ellcey <sje@cup.hp.com> writes:
> On IA64, extending a floating point operand in a register is a noop so
> it would be useful to fold that into actual floating point operations.
>
> So if I had something like:
>
>   ;; AF == Any floating point type that can fit in a register.
>   (define_mode_macro AF [(SF "") (DF "") (XF "")])
>
>   (define_insn "*addxf3_extend"
>     [(set (match_operand:XF 0 "fr_register_operand" "=f")
>           (plus:XF (float_extend:XF
>                      (match_operand:AF 1 "fr_register_operand" "%f"))
>                    (float_extend:XF
>                      (match_operand:AF 2 "fr_reg_or_fp01_operand" "fG"))))]
>     ""
>     "fadd %0 = %1, %F2"
>     [(set_attr "itanium_class" "fmac")])
>
> Am I right in assuming that this would allow two SF operands, two DF
> operands or two XF operands but would not allow, say, one SF operand and
> one DF operand?

'Fraid so.

> Could I work around that by defining AF1 and AF2 with the same
> definition as AF and then using AF1 and AF2 in the instruction instead
> of using AF twice?

That should certainly do the trick.  (Do you really want to
include XF though?  I'm not sure whether it's OK to have
(float_extend:XF (reg:XF ...)).)

> It would be nice if I could fold the version of addxf3 that has no
> float_extend's into this definition too but I don't think any macros or
> existing mechanism would allow me to do that.

Yeah, I know the feeling ;)  It would be nice to do the same thing
on MIPS with SI->DI sign_extends.

I did have one proposal for that:

   http://gcc.gnu.org/ml/gcc/2004-07/msg01126.html

but it didn't seem to take the world by storm ;)  It also doesn't
help when the extension isn't wrapping a matchd_operator.  I.e. it
wouldn't help to reduce the duplication between:

   (set (match_operand:DI ...)
        (sign_extend:DI (plus:SI (match_operand:SI ...)
                                 (match_operand:SI ...))))

and:

   (set (match_operand:SI ...)
        (plus:SI (match_operand:SI ...)
                 (match_operand:SI ...)))

which are the same thing on MIPS[*].  It would also run into problems
if the constraints allow constants, since you might end up reloading:

    (sign_extend:DI (reg:SI psuedo-equivalent-to-const))

to:

    (sign_extend:DI (const_int ...))

and that would be bad.

It would certainly be nice to have a clean way of dealing with this...

Richard

[*] We could probably handle that using match_operator though.