Optimized BiLiear 2D Up Sampling for AMD MI devices

Cherry-pick of #2729

Co-authored-by: glen-amd <[email protected]>

Author: rocm-repo-management-api[bot]

aten/src/ATen/native/cuda/UpSampleBilinear2d.cu

@@ -127,6 +127,29 @@ __global__ void upsample_bilinear2d_nhwc_out_frame(
   }
 }
 
+#ifdef USE_ROCM
+// Helper function to compute output pixel range that can contribute to input pixel
+template <typename accscalar_t>
+__device__ __forceinline__ void compute_output_range(
+    int input_pos,
+    accscalar_t scale,
+    int output_size,
+    bool align_corners,
+    int& min_output,
+    int& max_output) {
+  accscalar_t lo, hi;
+  if (align_corners) {
+      lo = static_cast<accscalar_t>(input_pos - 1) / scale;
+      hi = static_cast<accscalar_t>(input_pos + 1) / scale;
+  } else {
+      lo = (input_pos - static_cast<accscalar_t>(0.5)) / scale - static_cast<accscalar_t>(0.5);
+      hi = (input_pos + static_cast<accscalar_t>(1.5)) / scale - static_cast<accscalar_t>(0.5);
+  }
+  min_output = max(0, static_cast<int>(std::ceil(lo)));
+  max_output = min(output_size - 1, static_cast<int>(std::floor(hi)));
+}
+#endif
+
 // Backward (adjoint) operation 1 <- 2 (accumulates)
 template <typename scalar_t, typename accscalar_t>
 C10_LAUNCH_BOUNDS_1(1024)
@@ -141,8 +164,74 @@ __global__ void upsample_bilinear2d_backward_out_frame(
     const bool align_corners,
     scalar_t* __restrict__ idata,
     const scalar_t* __restrict__ odata) {
-  const size_t o_numel = nc * width2 * height2;
+  // In C++, integer multiplication, like in standard arithmetic, is generally commutative.
   const size_t i_numel = nc * width1 * height1;
+#ifdef USE_ROCM
+  for (size_t index = blockDim.x * blockIdx.x + threadIdx.x; index < i_numel;
+       index += blockDim.x * gridDim.x) {
+    // Decode input pixel coordinates
+    size_t index_temp = index;
+    const int w1 = index_temp % width1;
+    index_temp /= width1;
+    const int h1 = index_temp % height1;
+    const size_t nc_idx = index_temp / height1;
+
+    accscalar_t grad_sum = 0;
+
+    // Find range of output pixels that could interpolate from this input pixel
+    int h2_min, h2_max, w2_min, w2_max;
+    compute_output_range<accscalar_t>(h1, rheight, height2, align_corners, h2_min, h2_max);
+    compute_output_range<accscalar_t>(w1, rwidth, width2, align_corners, w2_min, w2_max);
+
+    // Iterate over potential output pixels
+    for (int h2 = h2_min; h2 <= h2_max; h2++) {
+      for (int w2 = w2_min; w2 <= w2_max; w2++) {
+        // Compute source coordinates for this output pixel
+        const accscalar_t h1r = area_pixel_compute_source_index<accscalar_t>(
+            rheight, h2, align_corners, /*cubic=*/false);
+        const int h1_base = (int)h1r;
+        const int h1p = (h1_base < height1 - 1) ? 1 : 0;
+        const accscalar_t h1lambda = h1r - h1_base;
+        const accscalar_t h0lambda = static_cast<accscalar_t>(1) - h1lambda;
+
+        const accscalar_t w1r = area_pixel_compute_source_index<accscalar_t>(
+            rwidth, w2, align_corners, /*cubic=*/false);
+        const int w1_base = (int)w1r;
+        const int w1p = (w1_base < width1 - 1) ? 1 : 0;
+        const accscalar_t w1lambda = w1r - w1_base;
+        const accscalar_t w0lambda = static_cast<accscalar_t>(1) - w1lambda;
+
+        // Check if our input pixel participates in this interpolation and accumulate all weights
+        // At boundaries, h1p=0 or w1p=0 causes some sampling positions to collapse
+        // to the same pixel, so we need to accumulate weights from all matching positions
+        accscalar_t weight = 0;
+
+        // Check all four interpolation positions and accumulate weights
+        if (h1 == h1_base && w1 == w1_base) {
+          weight += h0lambda * w0lambda;  // top-left
+        }
+        if (h1 == h1_base && w1 == w1_base + w1p) {
+          weight += h0lambda * w1lambda;  // top-right (may be same as top-left if w1p=0)
+        }
+        if (h1 == h1_base + h1p && w1 == w1_base) {
+          weight += h1lambda * w0lambda;  // bottom-left (may be same as top-left if h1p=0)
+        }
+        if (h1 == h1_base + h1p && w1 == w1_base + w1p) {
+          weight += h1lambda * w1lambda;  // bottom-right (may collapse to other positions)
+        }
+
+        if (weight > 0) {
+          const size_t output_idx = nc_idx * height2 * width2 + h2 * width2 + w2;
+          grad_sum += weight * static_cast<accscalar_t>(odata[output_idx]);
+        }
+      }
+    }
+
+    // Write accumulated gradient (no atomics needed)
+    idata[index] = static_cast<scalar_t>(grad_sum);
+  }
+#else
+  const size_t o_numel = nc * width2 * height2;
   for (size_t index = blockDim.x * blockIdx.x + threadIdx.x; index < o_numel;
        index += blockDim.x * gridDim.x) {
     size_t index_temp = index;
@@ -191,6 +280,7 @@ __global__ void upsample_bilinear2d_backward_out_frame(
         static_cast<scalar_t>(h1lambda * w1lambda * d2val),
         true);
   }
+#endif
 }
 
 template <typename scalar_t, typename accscalar_t>
@@ -387,7 +477,6 @@ static void upsample_bilinear2d_backward_out_cuda_template(
   // threads are not covering the whole input tensor.
   grad_input.zero_();
 
-  const size_t num_kernels = nbatch * channels * output_height * output_width;
   const int num_threads = std::min(
       at::cuda::getCurrentDeviceProperties()->maxThreadsPerBlock, 1024);
   cudaStream_t stream = at::cuda::getCurrentCUDAStream();
@@ -397,6 +486,12 @@ static void upsample_bilinear2d_backward_out_cuda_template(
     return;
   }
 
+#ifdef USE_ROCM
+  constexpr bool use_input = true;
+#else
+  constexpr bool use_input = false;
+#endif
+
   AT_DISPATCH_FLOATING_TYPES_AND2(
       at::ScalarType::Half, at::ScalarType::BFloat16,
       grad_output_.scalar_type(), "upsample_bilinear2d_backward_out_frame", [&] {
@@ -414,6 +509,8 @@ static void upsample_bilinear2d_backward_out_cuda_template(
       const accscalar_t rwidth = area_pixel_compute_scale<accscalar_t>(
           input_width, output_width, align_corners, scales_w);
 
+      const size_t num_kernels = nbatch * channels * output_height * output_width;
+
       upsample_bilinear2d_backward_nhwc_out_frame<scalar_t, accscalar_t>
           <<<ceil_div(num_kernels, static_cast<size_t>(num_threads)), num_threads, 0, stream>>>(
               input_height,
@@ -444,6 +541,8 @@ static void upsample_bilinear2d_backward_out_cuda_template(
       const accscalar_t rwidth = area_pixel_compute_scale<accscalar_t>(
           input_width, output_width, align_corners, scales_w);
 
+      const size_t num_kernels = nbatch * channels * (use_input ? input_height * input_width : output_height * output_width);
+
       upsample_bilinear2d_backward_out_frame<scalar_t, accscalar_t>
           <<<ceil_div(num_kernels, static_cast<size_t>(num_threads)),
              num_threads,