how would i set a register's lower bits to the lower bits of some register?

[Vega]

For that specific example you can do----

Code:

or r10, r11, r12

This does a logical OR with the values in r11 and r12, Result is written to r10. Anything in r10 beforehand is completed wiped out.

You also have the ability to use the Record feature (.) for a free use of cmpwi rX, 0 (rX being w/e register you are wanting to use)

Example:

Code:

or. r10, r11, r12 #Notice the dot in the instruction operand
bne+ some_label #Example branch