gas replaces instructions on sparc

[Ilya Basin]

Hi.
I have this in my .S file:
    clr  %o3
but in the compiled .o file I have:
    mov  %g0, %o3
Why does it happen? How to suppress it?

GNU assembler 2.15

SunOS blackbird 5.10 Generic_137137-09 sun4u sparc SUNW,Sun-Fire-280R