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Register count for feature transformer

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Compute optimal register count for feature transformer accumulation dynamically.
This also introduces a change where AVX512 would only use 8 registers instead of 16
(now possible due to a 2x increase in feature transformer size).

closes https://github.com/official-stockfish/Stockfish/pull/3543

No functional change
This commit is contained in:
Tomasz Sobczyk 2021-06-10 17:43:42 +02:00 • committed by Stéphane Nicolet
parent e1f181ee64
commit ce4c523ad3
1 changed files with 59 additions and 15 deletions
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74
src/nnue/nnue_feature_transformer.h
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@ -28,12 +28,17 @@
namespace Stockfish::Eval::NNUE {
using BiasType = std::int16_t;
using WeightType = std::int16_t;
using PSQTWeightType = std::int32_t;
// If vector instructions are enabled, we update and refresh the
// accumulator tile by tile such that each tile fits in the CPU's
// vector registers.
#define VECTOR
static_assert(PSQTBuckets == 8, "Assumed by the current choice of constants.");
static_assert(PSQTBuckets % 8 == 0,
"Per feature PSQT values cannot be processed at granularity lower than 8 at a time.");
#ifdef USE_AVX512
typedef __m512i vec_t;
@ -47,8 +52,7 @@ 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()
static constexpr IndexType NumRegs = 8; // only 8 are needed
static constexpr IndexType NumPsqtRegs = 1;
#define NumRegistersSIMD 32
#elif USE_AVX2
typedef __m256i vec_t;
@ -62,8 +66,7 @@ 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()
static constexpr IndexType NumRegs = 16;
static constexpr IndexType NumPsqtRegs = 1;
#define NumRegistersSIMD 16
#elif USE_SSE2
typedef __m128i vec_t;
@ -77,8 +80,7 @@ namespace Stockfish::Eval::NNUE {
#define vec_add_psqt_32(a,b) _mm_add_epi32(a,b)
#define vec_sub_psqt_32(a,b) _mm_sub_epi32(a,b)
#define vec_zero_psqt() _mm_setzero_si128()
static constexpr IndexType NumRegs = Is64Bit ? 16 : 8;
static constexpr IndexType NumPsqtRegs = 2;
#define NumRegistersSIMD (Is64Bit ? 16 : 8)
#elif USE_MMX
typedef __m64 vec_t;
@ -92,8 +94,7 @@ namespace Stockfish::Eval::NNUE {
#define vec_add_psqt_32(a,b) _mm_add_pi32(a,b)
#define vec_sub_psqt_32(a,b) _mm_sub_pi32(a,b)
#define vec_zero_psqt() _mm_setzero_si64()
static constexpr IndexType NumRegs = 8;
static constexpr IndexType NumPsqtRegs = 4;
#define NumRegistersSIMD 8
#elif USE_NEON
typedef int16x8_t vec_t;
@ -107,14 +108,61 @@ namespace Stockfish::Eval::NNUE {
#define vec_add_psqt_32(a,b) vaddq_s32(a,b)
#define vec_sub_psqt_32(a,b) vsubq_s32(a,b)
#define vec_zero_psqt() psqt_vec_t{0}
static constexpr IndexType NumRegs = 16;
static constexpr IndexType NumPsqtRegs = 2;
#define NumRegistersSIMD 16
#else
#undef VECTOR
#endif
#ifdef VECTOR
// Compute optimal SIMD register count for feature transformer accumulation.
// We use __m* types as template arguments, which causes GCC to emit warnings
// about losing some attribute information. This is irrelevant to us as we
// only take their size, so the following pragma are harmless.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wignored-attributes"
template <typename SIMDRegisterType,
typename LaneType,
int NumLanes,
int MaxRegisters>
static constexpr int BestRegisterCount()
{
#define RegisterSize sizeof(SIMDRegisterType)
#define LaneSize sizeof(LaneType)
static_assert(RegisterSize >= LaneSize);
static_assert(MaxRegisters <= NumRegistersSIMD);
static_assert(MaxRegisters > 0);
static_assert(NumRegistersSIMD > 0);
static_assert(RegisterSize % LaneSize == 0);
static_assert((NumLanes * LaneSize) % RegisterSize == 0);
const int ideal = (NumLanes * LaneSize) / RegisterSize;
if (ideal <= MaxRegisters)
return ideal;
// Look for the largest divisor of the ideal register count that is smaller than MaxRegisters
for (int divisor = MaxRegisters; divisor > 1; --divisor)
if (ideal % divisor == 0)
return divisor;
return 1;
}
static constexpr int NumRegs = BestRegisterCount<vec_t, WeightType, TransformedFeatureDimensions, NumRegistersSIMD>();
static constexpr int NumPsqtRegs = BestRegisterCount<psqt_vec_t, PSQTWeightType, PSQTBuckets, NumRegistersSIMD>();
#pragma GCC diagnostic pop
#endif
// Input feature converter
class FeatureTransformer {
@ -557,10 +605,6 @@ namespace Stockfish::Eval::NNUE {
#endif
}
using BiasType = std::int16_t;
using WeightType = std::int16_t;
using PSQTWeightType = std::int32_t;
alignas(CacheLineSize) BiasType biases[HalfDimensions];
alignas(CacheLineSize) WeightType weights[HalfDimensions * InputDimensions];
alignas(CacheLineSize) PSQTWeightType psqtWeights[InputDimensions * PSQTBuckets];