[caffe2] Add AVX512 support for box_cox operator (pytorch#143627)

Summary:
Reuse templetized implementation of box_cox caffe2 operator.
* Duplicate .cc file of AVX2
* change intrinsics functions to use AVX512 instructions
* override templates
* extend the caller to use new methods
* guard AVX512 with a gflag to allow smooth transition

Differential Revision: D67433457

Pull Request resolved: pytorch#143627
Approved by: https://github.com/hl475

Author: efiks

caffe2/perfkernels/batch_box_cox_avx512.cc

@@ -0,0 +1,118 @@
+#ifdef CAFFE2_PERF_USE_MKL
+#include <immintrin.h>
+
+// Enable compiler vectorized version only if numerical consistency is not
+// required between dev and opt versions - disabled for now
+#ifndef FAST_VECTORIZED_KERNEL
+#define CPU_CAPABILITY_AVX512
+#include <ATen/cpu/vec/vec.h>
+
+namespace at::vec {
+namespace {
+// Implements the vectorized version of std::max() operation,
+// which DOESNOT propagates NaN for second argument
+template <typename scalar_t>
+Vectorized<scalar_t> max(const Vectorized<scalar_t>& a, const Vectorized<scalar_t>& b);
+
+template <>
+Vectorized<double> max(const Vectorized<double>& a, const Vectorized<double>& b) {
+  // std::max(NaN, nonNan) -> NaN
+  return _mm512_max_pd(b, a);
+}
+
+template <>
+Vectorized<float> max(const Vectorized<float>& a, const Vectorized<float>& b) {
+  // std::max(NaN, nonNan) -> NaN
+  return _mm512_max_ps(b, a);
+}
+
+// Implements recieprocal method based on newton-rapson method
+// 1. user RCP approximiation
+// 2. update with RCP = RCP * (2 - X * RCP)
+template <typename scalar_t>
+Vectorized<scalar_t> fast_recieprocal(const Vectorized<scalar_t>& b);
+template <typename scalar_t>
+scalar_t fast_recieprocal(scalar_t b);
+
+template<>
+Vectorized<float> fast_recieprocal(const Vectorized<float>& b) {
+  auto minus2 = _mm512_set1_ps(-2.f);
+  auto rcp = _mm512_rcp14_ps(b);
+  rcp = _mm512_mul_ps(rcp,  _mm512_fnmsub_ps(rcp, b, minus2));
+  rcp = _mm512_mul_ps(rcp,  _mm512_fnmsub_ps(rcp, b, minus2));
+  return rcp;
+}
+
+template <>
+float fast_recieprocal(float b) {
+  auto minus2 = _mm_set_ss(-2.f);
+  auto b_reg = _mm_set_ss(b);
+  auto rcp = _mm_rcp_ss(b_reg);
+  rcp = _mm_mul_ss(rcp,  _mm_fnmsub_ss(rcp, b_reg, minus2));
+  rcp = _mm_mul_ss(rcp,  _mm_fnmsub_ss(rcp, b_reg, minus2));
+  return _mm_cvtss_f32(rcp);
+}
+
+template<>
+Vectorized<double> fast_recieprocal(const Vectorized<double>& b) {
+  auto minus2 = _mm512_set1_pd(-2.);
+  auto rcp = _mm512_rcp14_pd(b);
+  rcp = _mm512_mul_pd(rcp,  _mm512_fnmsub_pd(rcp, b, minus2));
+  rcp = _mm512_mul_pd(rcp,  _mm512_fnmsub_pd(rcp, b, minus2));
+  return rcp;
+}
+
+template <>
+double fast_recieprocal(double b) {
+  return 1./b;
+}
+} // namespace
+} // namespace at::vec
+#endif
+
+#include "caffe2/perfkernels/batch_box_cox_vec.h"
+
+namespace caffe2::details {
+
+template <typename T>
+void compute_batch_box_cox__avx512(
+    std::size_t N,
+    std::size_t D,
+    std::size_t block_size,
+    const T* self_data,
+    const T* __restrict lambda1_data,
+    const T* __restrict lambda2_data,
+    T* output_data) {
+      compute_batch_box_cox_vec_fma<T>(
+          N,
+          D,
+          block_size,
+          self_data,
+          lambda1_data,
+          lambda2_data,
+          output_data);
+    }
+
+// Vectorized version specializations for float and double
+template
+void compute_batch_box_cox__avx512<float>(
+  std::size_t N,
+  std::size_t D,
+  std::size_t block_size,
+  const float* self_data,
+  const float* __restrict lambda1_data,
+  const float* __restrict lambda2_data,
+  float* output_data);
+
+template
+void compute_batch_box_cox__avx512<double>(
+  std::size_t N,
+  std::size_t D,
+  std::size_t block_size,
+  const double* self_data,
+  const double* __restrict lambda1_data,
+  const double* __restrict lambda2_data,
+  double* output_data);
+
+} // namespace caffe2::detail
+#endif // CAFFE2_PERF_USE_MKL

caffe2/perfkernels/batch_box_cox_vec.h

@@ -21,7 +21,6 @@ void TileIndicesInPlace(std::vector<int>& v, const std::size_t D, const std::siz
     }
   }
 }
-}  // namespace
 
 // MKL VML function templates.
 template <typename T>
@@ -307,5 +306,6 @@ void compute_batch_box_cox_vec_fma(
     }
   }
 }
+}  // namespace
 
 }   // namespace caffe2::details