On a7xx, the max constlen for compute is increased to 512 vec4s or 8KB,
however the size of the LB was not increased beyond 40KB. A quick
calculation shows that 8KB of consts multiplied by 2 banks plus the
API maximum of 32KB shared memory would exceed 40KB. This means that
we can't always use a constlen of 512, and sometimes have to fall back
to 256 when a lot of shared memory is in use.
In the future, we can use similar calculations to figure out how much
"extra" shared memory is available for the backend to spill to, but we
currently don't support spilling to shared memory.
Fixes: 5879eaac18 ("ir3: Increase compute const size on a7xx")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34746>
Connor Abbott
ea9d694a7b