chore: import upstream snapshot with attribution

paddle/phi/kernels/cpu/add_position_encoding_grad_kernel.cc

@@ -0,0 +1,44 @@
+// Copyright (c) 2024 PaddlePaddle Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "paddle/phi/core/kernel_registry.h"
+#include "paddle/phi/kernels/funcs/eigen/common.h"
+
+namespace phi {
+
+template <typename T, typename Context>
+void AddPositionEncodingGradKernel(const Context& dev_ctx,
+                                   const DenseTensor& x_in,
+                                   const DenseTensor& out_grad,
+                                   float alpha,
+                                   float beta,
+                                   DenseTensor* x_grad) {
+  auto* dOut = &out_grad;
+  auto dout = EigenVector<T>::Flatten(*dOut);
+
+  auto* dX = x_grad;
+  dev_ctx.template Alloc<T>(dX);
+  auto dx = EigenVector<T>::Flatten(*dX);
+
+  auto* place = dev_ctx.eigen_device();
+  dx.device(*place) = dout * static_cast<T>(alpha);
+}
+}  // namespace phi
+
+PD_REGISTER_KERNEL(add_position_encoding_grad,
+                   CPU,
+                   ALL_LAYOUT,
+                   phi::AddPositionEncodingGradKernel,
+                   float,
+                   double) {}