Re: Question about "match_dup"

[Andrew Pinski <pinskia at physics dot uc dot edu>]

On Sunday, Sep 7, 2003, at 20:54 US/Pacific, Ian Lance Taylor wrote:

> <fishbaoz@hotmail.com> writes:
>
> > What is the exact meaning of "match_dup"?
> >
> > the following is extracted from "mips.md"
> >
> > (define_expand "movsicc"
> >   [(set (match_dup 4) (match_operand 1 "comparison_operator" ""))
> >    (set (match_operand:SI 0 "register_operand" "")
> >  (if_then_else:SI (match_dup 5)
> >     (match_operand:SI 2 "reg_or_0_operand" "")
> >     (match_operand:SI 3 "reg_or_0_operand" "")))]
> >   "mips_isa >= 4"
> >   "
> > {
> >   gen_conditional_move (operands);
> >   DONE;
> > }")
> >
> > Now?
> > what is the meaning of "match_dup" in the machine description above?
> > what does it "duplicate"? Operand(4)? where is the original 
> > Operand(4)?
>
> The preparation statements always call DONE.  That means that the RTL
> template is never used, and is in effect a comment.  The insns are
> generated by gen_conditional_move().

But match_dup is needed to get a fourth operand, this technic is used in
other machine descriptions (like ffssi2 in rs6000.md) and then you 
create
the operand.

(define_expand "ffssi2"
  [(set (match_dup 2)
        (neg:SI (match_operand:SI 1 "gpc_reg_operand" "r")))
   (parallel [(set (match_dup 3) (and:SI (match_dup 1)
                                         (match_dup 2)))
              (clobber (scratch:CC))])
   (set (match_dup 4) (clz:SI (match_dup 3)))
   (set (match_operand:SI 0 "gpc_reg_operand" "=r")
        (minus:SI (const_int 32) (match_dup 4)))]
  ""
  {
     operands[2] = gen_reg_rtx (SImode);
     operands[3] = gen_reg_rtx (SImode);
     operands[4] = gen_reg_rtx (SImode);
  })


Thanks,
Andrew Pinski