Small optimisations to q4_1 dot product (@Const-me)

Author: blackhole89

ggml.c

@@ -1582,12 +1582,19 @@ inline static void ggml_vec_dot_q4_1(const int n, float * restrict s, const void
         const uint8_t * restrict p0 = pb0 + i*QK/2;
         const uint8_t * restrict p1 = pb1 + i*QK/2;
 
+        const __m256 d0v = _mm256_broadcast_ss( d0 );
+        const __m256 d1v = _mm256_broadcast_ss( d1 );
+        const __m256 m0v = _mm256_broadcast_ss( m0 );
+        const __m256 m1v = _mm256_broadcast_ss( m1 );
+
+
         // Compute combined scale for the block
-        const __m256 scale_01 = _mm256_mul_ps( _mm256_broadcast_ss( d0 ), _mm256_broadcast_ss( d1 ) );
+        const __m256 scale_01 = _mm256_mul_ps( d0v, d1v );
 
         // Compute cross scales for the block
-        const __m256 scale_0 = _mm256_mul_ps( _mm256_broadcast_ss( d0 ), _mm256_broadcast_ss( m1 ) );
-        const __m256 scale_1 = _mm256_mul_ps( _mm256_broadcast_ss( m0 ), _mm256_broadcast_ss( d1 ) );
+        const __m256 scale_0 = _mm256_mul_ps( d0v, m1v );
+        const __m256 scale_1 = _mm256_mul_ps( m0v, d1v );
+        const __m256 cross_scales = _mm256_blend_ps( scale_0, scale_1, 0b10101010 );
 
         // Load 16 bytes, and unpack 4 bit fields into bytes, making 32 bytes
         __m256i bx = bytesFromNibbles( p0 );
@@ -1608,20 +1615,22 @@ inline static void ggml_vec_dot_q4_1(const int n, float * restrict s, const void
         i32 = _mm256_add_epi32( i32, _mm256_madd_epi16( x16_h, y16_h ) );
 
         // compute sums of unsigned bytes in bx, by in blocks of 8.
-        // This results in a layout like S100 0000 S200 0000 S300 0000 S400 0000,
-        // so if we then cast to 8 singles, we get 8 floats like [ s0_7, 0.0, s8_15, 0.0, s16_23, 0.0, s24_31, 0.0 ]
-        __m256 xsum = _mm256_cvtepi32_ps( _mm256_sad_epu8( bx, _mm256_setzero_si256() ) );
-        __m256 ysum = _mm256_cvtepi32_ps( _mm256_sad_epu8( by, _mm256_setzero_si256() ) );
+        // This results in a layout like X100 0000 X200 0000 X300 0000 X400 0000,
+        // which we then interleave as X100 Y100 X200 Y200 X300 Y300 X400 Y400.
+        // so if we then cast to 8 singles, we get 8 floats like [ x0_7, y0_7, x8_15, y8_15, x16_23, y16_23, x24_31, y24_31 ]
+        __m256i xsumi = _mm256_sad_epu8( bx, _mm256_setzero_si256() );
+        __m256i ysumi = _mm256_sad_epu8( by, _mm256_setzero_si256() );
+        __m256i sumsi = _mm256_or_si256( xsumi, _mm256_slli_si256( ysumi, 4 ) );
+        __m256  sums  = _mm256_cvtepi32_ps( sumsi );
 
         // Convert int32_t to float
         __m256 p = _mm256_cvtepi32_ps( i32 );
         // Apply the scale, and accumulate
         // acc += d0*d1*x*y + d0*m1*x + d1*m0*y
         acc = _mm256_fmadd_ps( scale_01, p, acc );
-        acc = _mm256_fmadd_ps( scale_0, xsum, acc );
-        acc = _mm256_fmadd_ps( scale_1, ysum, acc );
+        acc = _mm256_fmadd_ps( cross_scales, sums, acc );
         // acc_offset += m0*m1 (for each entry in the block)
-        acc_offset += (*m0)*(*m1)*QK;
+        acc_offset += (*m0)*(*m1);
     }
 
     // Return horizontal sum of the acc vector
@@ -1630,7 +1639,7 @@ inline static void ggml_vec_dot_q4_1(const int n, float * restrict s, const void
     res = _mm_add_ps( res, _mm_movehl_ps( res, res ) );
     res = _mm_add_ss( res, _mm_movehdup_ps( res ) );
 
-    sumf = _mm_cvtss_f32( res ) + acc_offset;
+    sumf = _mm_cvtss_f32( res ) + acc_offset * QK;
 #else
 #error "not implemented for QK"
 #endif