Clobber REG_CC only for some constraint alternatives?

[Senthil Kumar Selvaraj via Gcc]

Hi,

  I'm working on porting AVR to MODE_CC, and there are quite a few
  patterns that clobber the condition code reg only for certain
  constraint alternatives. For e.g.,

(define_insn "mov<mode>_insn"
  [(set (match_operand:ALL1 0 "nonimmediate_operand" "=r    ,d    ,Qm   ,r 
,q,r,*r")
        (match_operand:ALL1 1 "nox_general_operand"   "r Y00,n Ynn,r 
Y00,Qm,r,q,i"))]
 "register_operand (operands[0], <MODE>mode)
 || reg_or_0_operand (operands[1], <MODE>mode)"
 {
      return output_movqi (insn, operands, NULL);
 }
 [(set_attr "length" "1,1,5,5,1,1,4")
 (set_attr "adjust_len" "mov8")
 (set_attr "cc" "ldi,none,clobber,clobber,none,none,clobber")])

As you can deduce from the (set_attr "cc" ..), only constraint
alternatives 0,2,3 and 6 clobber CC - others leave it unchanged.

My first version of the port adds a post-reload splitter that adds a
(clobber (reg:CC REG_CC)) unconditionally, and it appears to work. If I
do want to add the clobber conditionally, would something like the below
be a good way to do it (get_cc_reg_clobber_rtx returns either const0_rtx
or cc_reg_rtx based on get_attr_cc (insn))? Or is there a better/cleaner way?

(define_insn_and_split "mov<mode>_insn"
  [(set (match_operand:ALL1 0 "nonimmediate_operand" "=r    ,d    ,Qm   ,r 
,q,r,*r")
        (match_operand:ALL1 1 "nox_general_operand"   "r Y00,n Ynn,r 
Y00,Qm,r,q,i"))]
  "register_operand (operands[0], <MODE>mode)
    || reg_or_0_operand (operands[1], <MODE>mode)"
  "#"
  "&& reload_completed"
  [(parallel [(set (match_dup 0)
                   (match_dup 1))
              (clobber (match_dup 2))])]
  {
    operands[2] = get_cc_reg_clobber_rtx (curr_insn);
  }
  [(set_attr "cc" "ldi,none,clobber,clobber,none,none,clobber")])

(define_insn "*mov<mode>_insn_clobber_flags"
  [(set (match_operand:ALL1 0 "nonimmediate_operand" "=r    ,Qm   ,r ,*r")
        (match_operand:ALL1 1 "nox_general_operand"   "r Y00,r Y00,Qm,i"))
   (clobber (reg:CC REG_CC))]
  "(register_operand (operands[0], <MODE>mode)
    || reg_or_0_operand (operands[1], <MODE>mode))
   && reload_completed"
  {
    return output_movqi (insn, operands, NULL);
  }
  [(set_attr "length" "1,5,5,4")
   (set_attr "adjust_len" "mov8")])

(define_insn "*mov<mode>_insn_noclobber_flags"
  [(set (match_operand:ALL1 0 "nonimmediate_operand" "=r,d   ,q,r")
        (match_operand:ALL1 1 "nox_general_operand"   "r,n Ynn,r,q"))
   (clobber (const_int 0))]
  "(register_operand (operands[0], <MODE>mode)
    || reg_or_0_operand (operands[1], <MODE>mode))
   && reload_completed"
  {
    return output_movqi (insn, operands, NULL);
  }
  [(set_attr "length" "1,1,1,1")
   (set_attr "adjust_len" "mov8")])

Regards
Senthil