perf(arm_common): optimize sigmoid

GitOrigin-RevId: 7cb248a15b447f4fbb0008e419cdf07cf6387309

dnn/src/arm_common/elemwise/neon_mathfun.cpp

@@ -371,6 +371,69 @@ v4sf tan_ps_f32(v4sf x) {
 #undef c_cephes_log_q1
 #undef c_cephes_log_q2
 
+static const struct {
+    float lower_range;
+    float upper_range;
+    float alpha_9;
+    float alpha_7;
+    float alpha_5;
+    float alpha_3;
+    float alpha_1;
+    float beta_10;
+    float beta_8;
+    float beta_6;
+    float beta_4;
+    float beta_2;
+    float beta_0;
+    float one_half;
+} sigmoid_constants = {
+        -18.0f,
+        18.0f,
+        4.37031012579801e-11f,
+        1.15627324459942e-07f,
+        6.08574864600143e-05f,
+        8.51377133304701e-03f,
+        2.48287947061529e-01f,
+        6.10247389755681e-13f,
+        5.76102136993427e-09f,
+        6.29106785017040e-06f,
+        1.70198817374094e-03f,
+        1.16817656904453e-01f,
+        9.93151921023180e-01f,
+        0.5f,
+};
+
+v4sf sigmoid_ps_f32(v4sf src) {
+    auto val = vmaxq_f32(vdupq_n_f32(sigmoid_constants.lower_range), src);
+    val = vminq_f32(vdupq_n_f32(sigmoid_constants.upper_range), val);
+    auto squared = vmulq_f32(val, val);
+    auto p = vmlaq_f32(
+            vdupq_n_f32(sigmoid_constants.alpha_7), squared,
+            vdupq_n_f32(sigmoid_constants.alpha_9));
+    p = vmlaq_f32(vdupq_n_f32(sigmoid_constants.alpha_5), p, squared);
+    p = vmlaq_f32(vdupq_n_f32(sigmoid_constants.alpha_3), p, squared);
+    p = vmlaq_f32(vdupq_n_f32(sigmoid_constants.alpha_1), p, squared);
+    p = vmulq_f32(p, val);
+    auto q = vmlaq_f32(
+            vdupq_n_f32(sigmoid_constants.beta_8), squared,
+            vdupq_n_f32(sigmoid_constants.beta_10));
+    q = vmlaq_f32(vdupq_n_f32(sigmoid_constants.beta_6), q, squared);
+    q = vmlaq_f32(vdupq_n_f32(sigmoid_constants.beta_4), q, squared);
+    q = vmlaq_f32(vdupq_n_f32(sigmoid_constants.beta_2), q, squared);
+    q = vmlaq_f32(vdupq_n_f32(sigmoid_constants.beta_0), q, squared);
+    return vaddq_f32(div_ps_f32(p, q), vdupq_n_f32(sigmoid_constants.one_half));
+}
+
+#if __ARM_FEATURE_FP16_VECTOR_ARITHMETIC
+float16x8_t sigmoid_ps_f16(float16x8_t x) {
+    float32x4_t low = vcvt_f32_f16(vget_low_f16(x));
+    float32x4_t high = vcvt_f32_f16(vget_high_f16(x));
+    low = sigmoid_ps_f32(low);
+    high = sigmoid_ps_f32(high);
+    return vcombine_f16(vcvt_f16_f32(low), vcvt_f16_f32(high));
+}
+#endif
+
 }  // namespace arm_common
 }  // namespace megdnn
 

dnn/src/arm_common/elemwise/neon_mathfun.h

@@ -54,11 +54,38 @@ v4sf cos_ps_f32(v4sf x);
 
 v4sf tan_ps_f32(v4sf x);
 
+static inline v4sf div_ps_f32(v4sf x, v4sf y) {
+#if MEGDNN_AARCH64
+    return vdivq_f32(x, y);
+#else
+    //! armv7 not support vdiv, so compute the reciprocal and iterate again
+    float32x4_t recp = vrecpeq_f32(y);
+    recp = vmulq_f32(vrecpsq_f32(y, recp), recp);
+    return vmulq_f32(x, recp);
+#endif
+}
+
+v4sf sigmoid_ps_f32(v4sf x);
+
 #if __ARM_FEATURE_FP16_VECTOR_ARITHMETIC
 /**
  * \brief compute for 8 half at once, the inner just invoke exp_ps_f32 twice
  */
 float16x8_t exp_ps_f16(float16x8_t x);
+
+static inline float16x8_t div_ps_f16(float16x8_t x, float16x8_t y) {
+#if MEGDNN_AARCH64
+    return vdivq_f16(x, y);
+#else
+    //! armv7 not support vdiv, so compute the reciprocal and iterate again
+    float16x8_t recp = vrecpeq_f16(y);
+    recp = vmulq_f16(vrecpsq_f16(y, recp), recp);
+    return vmulq_f16(x, recp);
+#endif
+}
+
+float16x8_t sigmoid_ps_f16(float16x8_t x);
+
 #endif
 
 }  // namespace arm_common

dnn/src/arm_common/elemwise_helper/kimpl/fuse_add_sigmoid.h

@@ -47,24 +47,14 @@ struct FuseAddSigmoidOp;
             vst1q_##_func_suffix(dst + SIMD_WIDTH, vitem.val[1]);                     \
         }                                                                             \
         _neon_type operator()(const _neon_type& src0, const _neon_type& src1) const { \
-            auto zero_val = vdupq_n_##_func_suffix(0.f);                              \
-            auto one_val = vdupq_n_##_func_suffix(1.f);                               \
             auto val1 = src0.val[0];                                                  \
             auto val2 = src0.val[1];                                                  \
             auto val3 = src1.val[0];                                                  \
             auto val4 = src1.val[1];                                                  \
             val1 = vaddq_##_func_suffix(val1, val3);                                  \
             val2 = vaddq_##_func_suffix(val2, val4);                                  \
-            val1 = vsubq_##_func_suffix(zero_val, val1);                              \
-            val2 = vsubq_##_func_suffix(zero_val, val2);                              \
-            val1 = exp_ps_##_func_suffix(val1);                                       \
-            val2 = exp_ps_##_func_suffix(val2);                                       \
-            auto recipe1 = vaddq_##_func_suffix(one_val, val1);                       \
-            auto recipe2 = vaddq_##_func_suffix(one_val, val2);                       \
-            val1 = vrecpeq_##_func_suffix(recipe1);                                   \
-            val2 = vrecpeq_##_func_suffix(recipe2);                                   \
-            val1 = vmulq_##_func_suffix(vrecpsq_##_func_suffix(recipe1, val1), val1); \
-            val2 = vmulq_##_func_suffix(vrecpsq_##_func_suffix(recipe2, val2), val2); \
+            val1 = sigmoid_ps_##_func_suffix(val1);                                   \
+            val2 = sigmoid_ps_##_func_suffix(val2);                                   \
             return {{val1, val2}};                                                    \
         }                                                                             \
     };

dnn/src/arm_common/elemwise_helper/kimpl/sigmoid.h

@@ -52,14 +52,7 @@ struct SigmoidOp;
             return {{operator()(src.val[0]), operator()(src.val[1])}}; \
         }                                                              \
         _neon_type operator()(const _neon_type& src) const {           \
-            auto zero_val = vdupq_n_##_func_suffix(0.f);                              \
-            auto one_val = vdupq_n_##_func_suffix(1.f);                               \
-            auto val1 = vsubq_##_func_suffix(zero_val, src);                          \
-            val1 = exp_ps_##_func_suffix(val1);                                       \
-            auto recipe1 = vaddq_##_func_suffix(one_val, val1);                       \
-            val1 = vrecpeq_##_func_suffix(recipe1);                                   \
-            val1 = vmulq_##_func_suffix(vrecpsq_##_func_suffix(recipe1, val1), val1); \
-            return val1;                                                              \
+            return sigmoid_ps_##_func_suffix(src);                     \
         }                                                              \
     };
 OP(dt_float32, float32x4_t, float32x4x2_t, f32, 4)

imperative/python/test/unit/utils/test_network.py

@@ -318,7 +318,7 @@ def test_add_remove_output():
     out = g.run(a.numpy(), b.numpy())
 
     np.testing.assert_equal(out["new_o1"], ((a + b) * 3).numpy())
-    np.testing.assert_equal(out["new_o2"], (F.sigmoid((a + b))).numpy())
+    np.testing.assert_almost_equal(out["new_o2"], (F.sigmoid((a + b))).numpy())
 
 
 def test_query():