[PATCH] rs6000: Generate _Decimal128 to _Decimal32 hardware conversion instructions

[Segher Boessenkool]

On Fri, Jul 17, 2020 at 04:18:55PM -0500, Peter Bergner wrote:
> On 7/17/20 3:23 PM, Segher Boessenkool wrote:
> > On ISA 3.0B and later you can do
> > 
> > 	mffscdrni %3,7
> > 	drdpq %2,%1
> > 	mffscdrn %3,%3
> > 	drsp %0,%2
> > 
> > (saving one insn, and using somewhat cheaper insns).  But that is only
> > on newer machines, so is this worth it at all?  :-)
> 
> So something like the following?
> 
> Peter
> 
> 
> (define_insn "trunctdsd2"
>   [(set (match_operand:SD 0 "gpc_reg_operand" "=d")
>         (float_truncate:SD (match_operand:TD 1 "gpc_reg_operand" "d")))
>    (clobber (match_scratch:TD 2 "=&d"))
>    (clobber (match_scratch:DF 3 "=&d"))]
>   "TARGET_DFP"
> {
>   if (TARGET_MODULO)
>     return "mffscdrni %3,7\;drdpq %2,%1\;mffscdrn %3,%3\;drsp %0,%2";
>   else
>     return "mffs %3\;mtfsfi 7,7,1\;drdpq %2,%1\;mtfsf 0xff,%3,1,0\;drsp %0,%2";
> }
>   [(set_attr "type" "dfp")
>    (set (attr "length")
>         (if_then_else
>           (match_test "TARGET_MODULO")
>           (const_string "16")
>           (const_string "20")))])

Well, just make an "isa" value of "p9"?  Then you can just do

(define_insn "trunctdsd2"
  [(set (match_operand:SD 0 "gpc_reg_operand" "=d")
        (float_truncate:SD (match_operand:TD 1 "gpc_reg_operand" "d")))
   (clobber (match_scratch:TD 2 "=&d"))
   (clobber (match_scratch:DF 3 "=&d"))]
  "TARGET_DFP"
  "@
   mffscdrni %3,7\;drdpq %2,%1\;mffscdrn %3,%3\;drsp %0,%2
   mffs %3\;mtfsfi 7,7,1\;drdpq %2,%1\;mtfsf 0xff,%3,1,0\;drsp %0,%2"
  [(set_attr "type" "dfp")
   (set_attr "isa" "p9,*")
   (set_attr "length" "16,20")])


Segher