This patch is a rewrite of nir_opt_move.
Differently from the previous version, each instruction is checked
if it can be moved downwards and then inserted before the first user
of the definition. The advantage is that less insert operations are
performed, the original order is kept if two movable instructions have
the same first user, and instructions without user in the same block
are moved towards the end.
v2: Only return true if an instruction really changed the position.
Don't care for discards, this will be handled by another MR.
v3: fix self-referring phis and update according to nir_can_move_instr().
v4: use nir_can_move_instr() and nir_instr_ssa_def()
v5: deduplicate some code
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3657>
Daniel Schürmann
8a78706643