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paddlepaddle--paddle/paddle/phi/kernels/cpu/broadcast_tensors_grad_kernel.cc
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2026-07-13 12:40:42 +08:00

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// Copyright (c) 2022 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/kernels/broadcast_tensors_grad_kernel.h"
#include <vector>
#include "paddle/phi/core/dense_tensor.h"
#include "paddle/phi/core/enforce.h"
#include "paddle/phi/core/kernel_registry.h"
#include "paddle/phi/kernels/full_kernel.h"
#include "paddle/phi/kernels/funcs/eigen/common.h"
#include "paddle/phi/kernels/funcs/eigen/eigen_function.h"
#include "paddle/phi/kernels/funcs/math_function.h"
#define SWITCH_RESHAPE_DIMS(n) \
case n: { \
Eigen::DSizes<int64_t, n> reshape_dims; \
for (size_t i = 0; i < reshape_dims_vec.size(); ++i) { \
reshape_dims[i] = reshape_dims_vec[i]; \
} \
dX.device(place) = \
dOut.reshape(reshape_dims).sum(reduce_dims).reshape(dX.dimensions()); \
break; \
}
#define UPPER_SWITCH_REDUCE_DIMS(m) \
case m: { \
Eigen::DSizes<int64_t, m> reduce_dims; \
for (size_t i = 0; i < reduce_dims_vec.size(); ++i) { \
reduce_dims[i] = reduce_dims_vec[i]; \
} \
switch (reshape_size) {
#define LOWER_SWITCH_REDUCE_DIMS \
default: { \
PADDLE_THROW(errors::InvalidArgument( \
"Detected reshape size: %d out of range. " \
"Minimum value should be larger than reduce size %d. " \
"While maximum supported is: 5", \
reshape_size, \
reduce_size)); \
} \
} \
break; \
}
namespace phi {
template <typename T, typename Context>
void BroadcastTensorsGradKernel(const Context& dev_ctx,
const std::vector<const DenseTensor*>& inputs,
const std::vector<const DenseTensor*>& dout,
std::vector<DenseTensor*> dx) {
(void)inputs;
// Find reduce dimensions
const auto& in_tensors = dout;
auto& out_tensors = dx;
size_t num_ins = in_tensors.size();
if (dout[0] && dout[0]->numel() == 0) {
for (auto dx : out_tensors) {
if (dx) Full<T, Context>(dev_ctx, dx->dims(), 0, dx);
}
return;
}
PADDLE_ENFORCE_GT(
num_ins,
1,
errors::InvalidArgument(
"Expected at least 2 input tensors, but only received %d.",
in_tensors.size()));
PADDLE_ENFORCE_EQ(num_ins,
out_tensors.size(),
errors::InvalidArgument(
"BroadcastTensorsOp expects equal number of inputs and "
"outputs, but received: %d inputs v.s %d outputs",
num_ins,
out_tensors.size()));
// For each In-Out tensor pair,
// Prepare and apply broadcast dims array
for (size_t i = 0; i < num_ins; i++) {
const auto* input_tensor = in_tensors[i];
auto* output_tensor = out_tensors[i];
const auto& input_dims = input_tensor->dims();
const auto& output_dims = output_tensor->dims();
int in_rank = input_dims.size();
int out_rank = output_dims.size();
// BroadcastTensorsGrad is simply a reduce_sum along broadcasted axes
// Here we perform the following Eigen operations:
// dOut(Flattened) -> reshape(reshape_dims) -> reduce(reduce_dims) ->
// reshape(dX_shape) -> dX
// Note the last "reshape(dX_shape)" will be performed implicitly,
// and we only need to collect reduce_dims and reshape_dims
std::vector<int> reduce_dims_vec;
std::vector<int> reshape_dims_vec;
for (int j = 0; j < in_rank; j++) {
int out_axis = out_rank - j - 1;
int in_axis = in_rank - j - 1;
reshape_dims_vec.push_back(static_cast<int>(input_dims[j]));
if (out_axis < 0 || output_dims[out_axis] != input_dims[in_axis]) {
reduce_dims_vec.push_back(in_axis);
}
}
size_t reduce_size = reduce_dims_vec.size();
size_t reshape_size = reshape_dims_vec.size();
bool just_copy = (reduce_dims_vec.empty());
dev_ctx.template Alloc<T>(output_tensor);
if (just_copy) {
// If this turns out to be a No-Op, simply perform a tensor copy
Copy(dev_ctx, *input_tensor, dev_ctx.GetPlace(), false, output_tensor);
} else {
PADDLE_ENFORCE_GE(
reduce_dims_vec.size(),
1,
errors::InvalidArgument("The number of dimensions of the input "
"'Out@GRAD' for Op(broadcast_tensors)"
" must be greater than or equal to 1, but "
"the value received is %d.",
reduce_dims_vec.size()));
PADDLE_ENFORCE_LE(
reduce_dims_vec.size(),
5,
errors::InvalidArgument(
"The number of dimensions of the input 'Out@GRAD' "
"for Op(broadcast_tensors) must be less than or equal "
"to 5, but the value received is %d.",
reduce_dims_vec.size()));
// Overall:
// dOut(Flattened) -> reshape(reshape_dims) -> reduce(reduce_dims) ->
// reshape(dX_shape) -> dX
auto dX = EigenVector<T>::Flatten(*output_tensor);
auto dOut = EigenVector<T>::Flatten(*input_tensor);
auto& place = *dev_ctx.eigen_device();
// Expand ReduceSize and ReshapeSize into static values
switch (reduce_size) {
UPPER_SWITCH_REDUCE_DIMS(1)
SWITCH_RESHAPE_DIMS(1)
SWITCH_RESHAPE_DIMS(2)
SWITCH_RESHAPE_DIMS(3)
SWITCH_RESHAPE_DIMS(4)
SWITCH_RESHAPE_DIMS(5)
LOWER_SWITCH_REDUCE_DIMS
UPPER_SWITCH_REDUCE_DIMS(2)
SWITCH_RESHAPE_DIMS(2)
SWITCH_RESHAPE_DIMS(3)
SWITCH_RESHAPE_DIMS(4)
SWITCH_RESHAPE_DIMS(5)
LOWER_SWITCH_REDUCE_DIMS
UPPER_SWITCH_REDUCE_DIMS(3)
SWITCH_RESHAPE_DIMS(3)
SWITCH_RESHAPE_DIMS(4)
SWITCH_RESHAPE_DIMS(5)
LOWER_SWITCH_REDUCE_DIMS
UPPER_SWITCH_REDUCE_DIMS(4)
SWITCH_RESHAPE_DIMS(4)
SWITCH_RESHAPE_DIMS(5)
LOWER_SWITCH_REDUCE_DIMS
UPPER_SWITCH_REDUCE_DIMS(5)
SWITCH_RESHAPE_DIMS(5)
LOWER_SWITCH_REDUCE_DIMS
default: {
PADDLE_THROW(
errors::InvalidArgument("Detected reduce size: %d out of range. "
"While maximum supported is: 5",
reduce_size));
}
}
}
}
}
} // namespace phi
PD_REGISTER_KERNEL(broadcast_tensors_grad,
CPU,
ALL_LAYOUT,
phi::BroadcastTensorsGradKernel,
int,
int64_t,
float,
double,
phi::float16,
phi::complex64,
phi::complex128) {}