Use vdotq_s32 to improve performance (#67)

* 10% performance boost on ARM

* Back to original change

Author: ggerganov

ggml.c

@@ -1360,34 +1360,20 @@ inline static void ggml_vec_dot_q4_0(const int n, float * restrict s, const void
         const int8x16_t v1_1hs = vsubq_s8(v1_1h, s8b);
 
         // dot product into int16x8_t
-        const int16x8_t pl0l = vmull_s8(vget_low_s8 (v0_0ls), vget_low_s8 (v1_0ls));
-        const int16x8_t pl0h = vmull_s8(vget_high_s8(v0_0ls), vget_high_s8(v1_0ls));
+        // assume that vdotq_s32 is always available, if not, should check for __ARM_FEATURE_DOTPROD
+        int32x4_t p_0 = vdotq_s32(vdupq_n_s32(0), v0_0ls, v1_0ls);
+        int32x4_t p_1 = vdotq_s32(vdupq_n_s32(0), v0_1ls, v1_1ls);
 
-        const int16x8_t ph0l = vmull_s8(vget_low_s8 (v0_0hs), vget_low_s8 (v1_0hs));
-        const int16x8_t ph0h = vmull_s8(vget_high_s8(v0_0hs), vget_high_s8(v1_0hs));
-
-        const int16x8_t pl1l = vmull_s8(vget_low_s8 (v0_1ls), vget_low_s8 (v1_1ls));
-        const int16x8_t pl1h = vmull_s8(vget_high_s8(v0_1ls), vget_high_s8(v1_1ls));
-
-        const int16x8_t ph1l = vmull_s8(vget_low_s8 (v0_1hs), vget_low_s8 (v1_1hs));
-        const int16x8_t ph1h = vmull_s8(vget_high_s8(v0_1hs), vget_high_s8(v1_1hs));
-
-        const int16x8_t pl_0 = vaddq_s16(pl0l, pl0h);
-        const int16x8_t ph_0 = vaddq_s16(ph0l, ph0h);
-
-        const int16x8_t pl_1 = vaddq_s16(pl1l, pl1h);
-        const int16x8_t ph_1 = vaddq_s16(ph1l, ph1h);
-
-        const int16x8_t p_0 = vaddq_s16(pl_0, ph_0);
-        const int16x8_t p_1 = vaddq_s16(pl_1, ph_1);
+        p_0 = vdotq_s32(p_0, v0_0hs, v1_0hs);
+        p_1 = vdotq_s32(p_1, v0_1hs, v1_1hs);
 
         // scalar
 #if defined(__ARM_FEATURE_QRDMX)
-        sum0 += d0_0*d1_0*vaddvq_s16(p_0);
-        sum1 += d0_1*d1_1*vaddvq_s16(p_1);
+        sum0 += d0_0*d1_0*vaddvq_s32(p_0);
+        sum1 += d0_1*d1_1*vaddvq_s32(p_1);
 #else
-        sum0 += d0_0*d1_0*(vgetq_lane_s16(p_0, 0) + vgetq_lane_s16(p_0, 1) + vgetq_lane_s16(p_0, 2) + vgetq_lane_s16(p_0, 3) + vgetq_lane_s16(p_0, 4) + vgetq_lane_s16(p_0, 5) + vgetq_lane_s16(p_0, 6) + vgetq_lane_s16(p_0, 7));
-        sum1 += d0_1*d1_1*(vgetq_lane_s16(p_1, 0) + vgetq_lane_s16(p_1, 1) + vgetq_lane_s16(p_1, 2) + vgetq_lane_s16(p_1, 3) + vgetq_lane_s16(p_1, 4) + vgetq_lane_s16(p_1, 5) + vgetq_lane_s16(p_1, 6) + vgetq_lane_s16(p_1, 7));
+        sum0 += d0_0*d1_0*(vgetq_lane_s32(p_0, 0) + vgetq_lane_s32(p_0, 1) + vgetq_lane_s32(p_0, 2) + vgetq_lane_s32(p_0, 3));
+        sum1 += d0_1*d1_1*(vgetq_lane_s32(p_1, 0) + vgetq_lane_s32(p_1, 1) + vgetq_lane_s32(p_1, 2) + vgetq_lane_s32(p_1, 3));
 #endif
     }