help with define_peephole2 condition

[Paul S <pauls at dataworx dot com dot au>]

When generating code for a two address machine (like x86) I'm 
trying to peephole sequences for commutative operations like

(destination registers on left)

1.    add    Rm,Rn
2.    ld       Rn,Rm

to

1.   add    Rn,Rm

I have defined this peephole2

define_peephole2
    [
        (parallel

            [
                (set (match_operand:HI 0 "register_operand" "")
                        (match_operator:HI 1 "commutative_operator"
                            [(match_dup 0)
                             (match_operand:HI 2 
"register_operand" "")]))
                (clobber (reg:CC CC_REGNUM))
            ]
        )
        (set (match_dup 2) (match_dup 0))
    ]
   "peep2_regno_dead_p( 2, REGNO (operands[0]))"
;    ""
    [
        (parallel
            [
                (set (match_dup 2)
                        (match_op_dup 1
                            [(match_dup 2)
                             (match_dup 0 )]))
                (clobber (reg:CC CC_REGNUM))
            ]
        )
    ]
)

which works perfectly when Rm is never referenced after 
instruction 2 in the original sequence, however it fails if Rm is 
defined in the instruction immediately after instruction 2.

e.g.

1.    add    r2,r0
2.    ld    r0,r2
3.    pop r2
4.    ret

where r0 is the function return value. To me it seems that r2 is 
dead between instructions 2 and 3 so this should be able to be 
converted to ...

1.    add    r0,r2
3.    pop r2
4.    ret

for this case the following is the  output from the peephole2 
pass. Note that R2 is not marked as dead in the (insn 33 24 27 2) 
sequence


(insn 24 20 33 2 (parallel [
            (set (reg:HIreg:2 [orig:18 D.1931 ] [18])
                (plus:HI (reg:HIreg:2 [orig:18 D.1931 ] [18])
                    (reg:HIreg:0)))
            (clobber (reg:CCreg:7))
        ]) tl.c:7 35 {addhi3}
     (expr_list:REG_DEAD (reg:HIreg:0)
        (expr_list:REG_DEAD (reg:HIreg:8)
            (expr_list:REG_UNUSED (reg:CCreg:7)
                (nil)))))

(insn 33 24 27 2 (set (reg/i:HIreg:0)
        (reg:HIreg:2 [orig:18 D.1931 ] [18])) tl.c:7 78 {*movhihi}
     (nil))

(insn 27 33 36 2 (use (reg/i:HIreg:0)) tl.c:7 -1
     (nil))

(note 36 27 37 2 NOTE_INSN_EPILOGUE_BEG)

Can anybody suggest a condition I should use in the 
define_peephole2 to correctly handle this circumstance ?

Thanks, Paul