What the constraint "o" in and<mode>3 means on MIPS backend

[Paul Hua <paul.hua.gm@xxxxxxxxx>]

Hi:

in mips.c:
...
3261 (define_insn "*and<mode>3"
3262   [(set (match_operand:GPR 0 "register_operand" "=d,d,d,!u,d,d,d,!u,d")
3263         (and:GPR (match_operand:GPR 1 "nonimmediate_operand"
"o,o,W,!u,d,d,d,0,d")

                                             ^
3264                  (match_operand:GPR 2 "and_operand"
"Yb,Yh,Yw,Uean,K,Yx,Yw,!u,d")))]
...

I do not find "o" in constraints.md and gcc internal.
what is the "o" means?


Paul.