Commit f695a9fed2 moved the 64-bit float <-> 16-bit float conversion
splitting into a core NIR pass, so the code remaining here is only
needed for 64-bit integer types.
Presumably in an attempt to remove the float handling, it replaced
simple bit_size == 64 checks with this expression:
(full_type & (nir_type_int64 | nir_type_uint64))
I believe that the intended expression was:
(full_type == nir_type_int64 || full_type == nir_type_uint64)
Unfortunately, the former is incorrect. Any integer or unsigned
NIR type would trigger the former expression. For example:
nir_type_uint32 & (nir_type_int64 | nir_type_uint64) => nir_type_uint
This meant that we were splitting e.g. u2f16 on 32-bit unsigned types
into u2f32 and f2f16, when we can easily natively handle that case.
To fix this, we go back to simple bit_size == 64 checks. This pass is
already run after nir_lower_fp16_casts which will split the float case,
so we will never see it here.
fossil-db on Alchemist shows a -1.14% reduction in affected shaders for
google-meet-clvk shaders. In another ChromeOS workload, it improves
performance by around 8% on Meteorlake.
Thanks to Sushma Venkatesh Reddy for finding this performance issue!
Fixes: f695a9fed2 ("intel/compiler: use nir_lower_fp16_casts")
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ivan Briano <ivan.briano@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30091>
