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b4ad3a3c4b
The sdot instruction computes (and accumulates) a signed dot product, which is quite handy for Stockfish's NNUE code. The instruction is optional for Armv8.2 and Armv8.3, and mandatory for Armv8.4 and above. The commit adds a new 'arm-dotprod' architecture with enabled dot product support. It also enables dot product support for the existing 'apple-silicon' architecture, which is at least Armv8.5. The following local speed test was performed on an Apple M1 with ARCH=apple-silicon. I had to remove CPU pinning from the benchmark script. However, the results were still consistent: Checking both binaries against themselves reported a speedup of +0.0000 and +0.0005, respectively. ``` Result of 100 runs ================== base (...ish.037ef3e1) = 1917997 +/- 7152 test (...fish.dotprod) = 2159682 +/- 9066 diff = +241684 +/- 2923 speedup = +0.1260 P(speedup > 0) = 1.0000 CPU: 10 x arm Hyperthreading: off ``` Fixes #4193 closes https://github.com/official-stockfish/Stockfish/pull/4400 No functional change