Using $REGUSE

I have a function with in-line assembly language. I preceed this function with:

#pragma	ASM

$REGUSE _population_count( A, B, R4, R5, R6, R7, DPH, DPL )

#pragma ENDASM

This tells the compiler which registers will be used by the function.

In fact, the function reads, but does not change R4, R5, R6 and R7.

Should $REGUSE list all the registers referenced by a function, or should it only list those registers that are actually changed?