adding movz to machine description

["Petar Bajic" <petar dot bajic at micronasnit dot com>]

I need to add conditional move instructions to gcc dlx port.
I found implemented pattern 'movmodecc' for conditional move instruction 
that look like this:
if (condition)
   a = b;
else
  a = c;

but my "movz" look like this

if (c == 0)
   a = b;

or asm: movz r1, r2, r3  ;; ((if r3 == 0, move r2 to r1))

there is no 'else'  branch.

In md file it's easy to describe first case:

(define_insn "movsicc_internal"
 [(set (match_operand:SI 0 "register_operand" "=d,d")
 (if_then_else:SI
 (match_operator 1 "comparison_operator" [(match_operand:SI 4 
"register_operand" "=d,d") (const_int 0)])
 (match_operand:SI 2 "register_operand" "=d,d")
 (match_operand:SI 3 "register_operand" "=d,d")))]

"movc\\t%0, %2, %3, %1" ;;theoretic conditional move with else branch
[(set_attr "mode" "SI")]

But I can't seem to describe what I need: conditional move without else 
branch.
Any help is appreciated. Im new here.

Petar