How to forbid register allocator to overlap bewteen DEST and SOURCE

[jiejie_rong]

Hi,

        GCC seems to overlap register bewteen DEST and SOURCE in different 
machine mode,

        Is there any target hooks to control this feature ?

        I use <Constraint Modifier> ‘&’ to forbid register allocator to overlap 
bewteen DEST and SOURCE,

        but there are some redundancy instructions in the result code :(

        Thanks a lot

—Jojo