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// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
#include <ATen/ATen.h>
#include <ATen/cuda/CUDAContext.h>
#include <THC/THC.h>
#include <THC/THCAtomics.cuh>
#include <THC/THCDeviceUtils.cuh>
// TODO make it in a common file
#define CUDA_1D_KERNEL_LOOP(i, n) \
for (int i = blockIdx.x * blockDim.x + threadIdx.x; i < n; \
i += blockDim.x * gridDim.x)
template <typename T>
__global__ void RoIPoolFForward(const int nthreads, const T* bottom_data,
const T spatial_scale, const int channels, const int height,
const int width, const int pooled_height, const int pooled_width,
const T* bottom_rois, T* top_data, int* argmax_data) {
CUDA_1D_KERNEL_LOOP(index, nthreads) {
// (n, c, ph, pw) is an element in the pooled output
int pw = index % pooled_width;
int ph = (index / pooled_width) % pooled_height;
int c = (index / pooled_width / pooled_height) % channels;
int n = index / pooled_width / pooled_height / channels;
const T* offset_bottom_rois = bottom_rois + n * 5;
int roi_batch_ind = offset_bottom_rois[0];
int roi_start_w = round(offset_bottom_rois[1] * spatial_scale);
int roi_start_h = round(offset_bottom_rois[2] * spatial_scale);
int roi_end_w = round(offset_bottom_rois[3] * spatial_scale);
int roi_end_h = round(offset_bottom_rois[4] * spatial_scale);
// Force malformed ROIs to be 1x1
int roi_width = max(roi_end_w - roi_start_w + 1, 1);
int roi_height = max(roi_end_h - roi_start_h + 1, 1);
T bin_size_h = static_cast<T>(roi_height)
/ static_cast<T>(pooled_height);
T bin_size_w = static_cast<T>(roi_width)
/ static_cast<T>(pooled_width);
int hstart = static_cast<int>(floor(static_cast<T>(ph)
* bin_size_h));
int wstart = static_cast<int>(floor(static_cast<T>(pw)
* bin_size_w));
int hend = static_cast<int>(ceil(static_cast<T>(ph + 1)
* bin_size_h));
int wend = static_cast<int>(ceil(static_cast<T>(pw + 1)
* bin_size_w));
// Add roi offsets and clip to input boundaries
hstart = min(max(hstart + roi_start_h, 0), height);
hend = min(max(hend + roi_start_h, 0), height);
wstart = min(max(wstart + roi_start_w, 0), width);
wend = min(max(wend + roi_start_w, 0), width);
bool is_empty = (hend <= hstart) || (wend <= wstart);
// Define an empty pooling region to be zero
T maxval = is_empty ? 0 : -FLT_MAX;
// If nothing is pooled, argmax = -1 causes nothing to be backprop'd
int maxidx = -1;
const T* offset_bottom_data =
bottom_data + (roi_batch_ind * channels + c) * height * width;
for (int h = hstart; h < hend; ++h) {
for (int w = wstart; w < wend; ++w) {
int bottom_index = h * width + w;
if (offset_bottom_data[bottom_index] > maxval) {
maxval = offset_bottom_data[bottom_index];
maxidx = bottom_index;
}
}
}
top_data[index] = maxval;
argmax_data[index] = maxidx;
}
}
template <typename T>
__global__ void RoIPoolFBackward(const int nthreads, const T* top_diff,
const int* argmax_data, const int num_rois, const T spatial_scale,
const int channels, const int height, const int width,
const int pooled_height, const int pooled_width, T* bottom_diff,
const T* bottom_rois) {
CUDA_1D_KERNEL_LOOP(index, nthreads) {
// (n, c, ph, pw) is an element in the pooled output
int pw = index % pooled_width;
int ph = (index / pooled_width) % pooled_height;
int c = (index / pooled_width / pooled_height) % channels;
int n = index / pooled_width / pooled_height / channels;
const T* offset_bottom_rois = bottom_rois + n * 5;
int roi_batch_ind = offset_bottom_rois[0];
int bottom_offset = (roi_batch_ind * channels + c) * height * width;
int top_offset = (n * channels + c) * pooled_height * pooled_width;
const T* offset_top_diff = top_diff + top_offset;
T* offset_bottom_diff = bottom_diff + bottom_offset;
const int* offset_argmax_data = argmax_data + top_offset;
int argmax = offset_argmax_data[ph * pooled_width + pw];
if (argmax != -1) {
atomicAdd(
offset_bottom_diff + argmax,
static_cast<T>(offset_top_diff[ph * pooled_width + pw]));
}
}
}
std::tuple<at::Tensor, at::Tensor> ROIPool_forward_cuda(const at::Tensor& input,
const at::Tensor& rois,
const float spatial_scale,
const int pooled_height,
const int pooled_width) {
AT_ASSERTM(input.device().is_cuda(), "input must be a CUDA tensor");
AT_ASSERTM(rois.device().is_cuda(), "rois must be a CUDA tensor");
auto num_rois = rois.size(0);
auto channels = input.size(1);
auto height = input.size(2);
auto width = input.size(3);
auto output = at::empty({num_rois, channels, pooled_height, pooled_width}, input.options());
auto output_size = num_rois * pooled_height * pooled_width * channels;
auto argmax = at::zeros({num_rois, channels, pooled_height, pooled_width}, input.options().dtype(at::kInt));
cudaStream_t stream = at::cuda::getCurrentCUDAStream();
dim3 grid(std::min(THCCeilDiv(output_size, 512L), 4096L));
dim3 block(512);
if (output.numel() == 0) {
THCudaCheck(cudaGetLastError());
return std::make_tuple(output, argmax);
}
AT_DISPATCH_FLOATING_TYPES(input.scalar_type(), "ROIPool_forward", [&] {
RoIPoolFForward<scalar_t><<<grid, block, 0, stream>>>(
output_size,
input.contiguous().data_ptr<scalar_t>(),
spatial_scale,
channels,
height,
width,
pooled_height,
pooled_width,
rois.contiguous().data_ptr<scalar_t>(),
output.data_ptr<scalar_t>(),
argmax.data_ptr<int>());
});
THCudaCheck(cudaGetLastError());
return std::make_tuple(output, argmax);
}
// TODO remove the dependency on input and use instead its sizes -> save memory
at::Tensor ROIPool_backward_cuda(const at::Tensor& grad,
const at::Tensor& input,
const at::Tensor& rois,
const at::Tensor& argmax,
const float spatial_scale,
const int pooled_height,
const int pooled_width,
const int batch_size,
const int channels,
const int height,
const int width) {
AT_ASSERTM(grad.device().is_cuda(), "grad must be a CUDA tensor");
AT_ASSERTM(rois.device().is_cuda(), "rois must be a CUDA tensor");
// TODO add more checks
auto num_rois = rois.size(0);
auto grad_input = at::zeros({batch_size, channels, height, width}, grad.options());
cudaStream_t stream = at::cuda::getCurrentCUDAStream();
dim3 grid(std::min(THCCeilDiv(grad.numel(), 512L), 4096L));
dim3 block(512);
// handle possibly empty gradients
if (grad.numel() == 0) {
THCudaCheck(cudaGetLastError());
return grad_input;
}
AT_DISPATCH_FLOATING_TYPES(grad.scalar_type(), "ROIPool_backward", [&] {
RoIPoolFBackward<scalar_t><<<grid, block, 0, stream>>>(
grad.numel(),
grad.contiguous().data_ptr<scalar_t>(),
argmax.data_ptr<int>(),
num_rois,
spatial_scale,
channels,
height,
width,
pooled_height,
pooled_width,
grad_input.data_ptr<scalar_t>(),
rois.contiguous().data_ptr<scalar_t>());
});
THCudaCheck(cudaGetLastError());
return grad_input;
}
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