nir/loop_analyze: use a sparse array and stop indexing SSA defs

Indexing SSA defs is unexpected behaviour and interferes with using
nir_loop_analyze_impl for validation.

It probably also breaks nir_metadata_live_defs.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32005>
1 file changed