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This is an experiment in using AVX-512 instructions to efficiently lookup
Unicode properties for runes. It turns out after benchmarking that this
is actually slower than a generic non-SIMD approach. My hypothesis is
that it’s slower due to the large latency of AVX-512 gather instructions
which are required to index the Unicode lookup tables.
UPDATE 1: After replacing the gather instructions with loads/stores and manual
for-loops to index data, the performance of the AVX-512 approach actually beats
the generic approach by a small margin (just under 10% or so).
UPDATE 2: Due to the fact that the Unicode tables take up a very large
amount of space, it’s ideal that you use the smallest datatypes possible.
After changing both the stage₁ and stage₂ tables to be arrays of bytes as
opposed to arrays of dwords, the AVX-512 implementation using gather
instructions no longer works however the variation using manual loops
with loads/stores does work, albeit slower. On a 27 MiB file the generic
implementation takes on average 82ms while the AVX-512 implementation
takes on average 77ms.
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