Reduce SIMD register count from 32 to 16

mstembera · vondele · commit 95fe2b9a9d33 · 2023-09-22T19:15:34.000+02:00
in the case of avx512 and vnni512 archs. Up to 17% speedup, depending on the compiler, e.g. ``` AMD pro 7840u (zen4 phoenix apu 4nm) bash bench_parallel.sh ./stockfish_avx512_gcc13 ./stockfish_avx512_pr_gcc13 20 10 sf_base = 1077737 +/- 8446 (95%) sf_test = 1264268 +/- 8543 (95%) diff = 186531 +/- 4280 (95%) speedup = 17.308% +/- 0.397% (95%) ``` Prior to this patch, it appears gcc spills registers. closes #4796 No functional change
diff --git a/src/nnue/nnue_feature_transformer.h b/src/nnue/nnue_feature_transformer.h
@@ -69,7 +69,7 @@ namespace Stockfish::Eval::NNUE {
   #define vec_add_psqt_32(a,b) _mm256_add_epi32(a,b)
   #define vec_sub_psqt_32(a,b) _mm256_sub_epi32(a,b)
   #define vec_zero_psqt() _mm256_setzero_si256()
-  #define NumRegistersSIMD 32
+  #define NumRegistersSIMD 16
   #define MaxChunkSize 64
 
   #elif USE_AVX2
