Right now it tries to place reg_write instructions as far up the
predecessor chain as possible. This is useful for a bunch of the passes
that call it since it ensures they don't get placed in dead blocks or in
single successors and things like that. But it screws up NAK's control
flow lowering so we need the option to turn it off and make the pass
place the reg_write instructions in the most obvious place possible.
Fixes: b013d54e4f ("nak/lower_cf: Flag phis as convergent when possible")
Reviewed-by: Mel Henning <mhenning@darkrefraction.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36914>