[ET-VK] Implement `native_group_norm (pytorch#11973)

## Changes

* Add implementation for the group norm operator.

The operator is implemented via a 2 stage implementation. First, a reduction operator is executed to calculate the mean and standard deviation of each channel group. Then, the normalization is applied in an elementwise fashion.

Differential Revision: [D77038778](https://our.internmc.facebook.com/intern/diff/D77038778/)

Author: pytorchbot

backends/vulkan/runtime/graph/ComputeGraph.cpp

@@ -272,6 +272,38 @@ vkapi::ScalarType ComputeGraph::dtype_of(const ValueRef idx) const {
   VK_THROW("Could not get dtype of value with type ", val.type());
 }
 
+bool ComputeGraph::is_contiguous_buffer_tensor(const ValueRef idx) const {
+  if (!val_is_tensor(idx)) {
+    return false;
+  }
+  if (!is_buffer_storage(idx)) {
+    return false;
+  }
+  return is_contiguous(idx);
+}
+
+bool ComputeGraph::is_standard_channels_packed_texture_tensor(
+    const ValueRef idx) const {
+  if (!val_is_tensor(idx)) {
+    return false;
+  }
+  if (is_buffer_storage(idx)) {
+    return false;
+  }
+  return has_standard_axis_map(idx) && packed_dim_of(idx) == 2;
+}
+
+bool ComputeGraph::is_standard_width_packed_texture_tensor(
+    const ValueRef idx) const {
+  if (!val_is_tensor(idx)) {
+    return false;
+  }
+  if (is_buffer_storage(idx)) {
+    return false;
+  }
+  return has_standard_axis_map(idx) && packed_dim_of(idx) == 0;
+}
+
 ValueRef ComputeGraph::add_tensor(
     const std::vector<int64_t>& sizes,
     const vkapi::ScalarType dtype,

backends/vulkan/runtime/graph/ComputeGraph.h

@@ -231,7 +231,7 @@ class ComputeGraph final {
   inline ptr_type get_##short_name(const ValueRef idx) {                   \
     return ptr_type(this, idx);                                            \
   }                                                                        \
-  inline bool val_is_##short_name(const ValueRef idx) {                    \
+  inline bool val_is_##short_name(const ValueRef idx) const {              \
     return values_.at(idx).is##type_name();                                \
   }
 
@@ -314,6 +314,32 @@ class ComputeGraph final {
     return values_.at(idx).toConstTensor().has_buffer_storage();
   }
 
+  /*
+   * Checks that the following is true:
+   * 1. The value at `idx` is a tensor
+   * 2. The tensor at `idx` has buffer storage
+   * 3. The buffer backed tensor at `idx` has a contiguous memory layout
+   */
+  bool is_contiguous_buffer_tensor(const ValueRef idx) const;
+
+  /*
+   * Checks that the following is true:
+   * 1. The value at `idx` is a tensor
+   * 2. The tensor at `idx` has texture storage
+   * 3. The texture backed tensor at `idx` has a standard axis mapping
+   * 4. The texture backed tensor at `idx` is channels packed
+   */
+  bool is_standard_channels_packed_texture_tensor(const ValueRef idx) const;
+
+  /*
+   * Checks that the following is true:
+   * 1. The value at `idx` is a tensor
+   * 2. The tensor at `idx` has texture storage
+   * 3. The texture backed tensor at `idx` has a standard axis mapping
+   * 4. The texture backed tensor at `idx` is width packed
+   */
+  bool is_standard_width_packed_texture_tensor(const ValueRef idx) const;
+
   inline bool val_is_view_of(const ValueRef maybe_view, const ValueRef base)
       const {
     return values_.at(maybe_view)
@@ -354,7 +380,7 @@ class ComputeGraph final {
     return values_.at(idx).toTensor().numel_ubo();
   }
 
-  inline bool has_standard_axis_map(const ValueRef idx) {
+  inline bool has_standard_axis_map(const ValueRef idx) const {
     return values_.at(idx).toTensor().has_standard_axis_map();
   }
 

backends/vulkan/runtime/graph/ops/glsl/group_norm_reduce_texture.glsl

@@ -0,0 +1,189 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#version 450 core
+
+#include "broadcasting_utils.h"
+#include "indexing_utils.h"
+
+#define PRECISION ${PRECISION}
+
+#define BUF_T ${buffer_scalar_type(DTYPE)}
+
+${define_required_extensions(DTYPE)}
+
+layout(std430) buffer;
+
+${layout_declare_tensor(B, "w", "t_mean", DTYPE, "buffer")}
+${layout_declare_tensor(B, "w", "t_rstd", DTYPE, "buffer")}
+
+${layout_declare_tensor(B, "r", "t_in", DTYPE, "texture3d")}
+
+${layout_declare_ubo(B, "ivec4", "mean_strides")}
+${layout_declare_ubo(B, "int", "mean_numel")}
+${layout_declare_ubo(B, "ivec3", "in_limits")}
+${layout_declare_ubo(B, "ivec4", "in_sizes")}
+
+layout(push_constant) uniform PRECISION restrict Block {
+  int group;
+  float epsilon;
+};
+
+layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
+
+${layout_declare_spec_const(C, "int", "mean_layout", "DEFAULT_DIM_ORDER")}
+const lowp ivec4 mean_dim_order = unhash_dim_order(mean_layout);
+
+#define LOCAL_WORK_GROUP_SIZE 64
+shared float shared_sum[LOCAL_WORK_GROUP_SIZE];
+shared float shared_sum_sq[LOCAL_WORK_GROUP_SIZE];
+
+/*
+ * Computes the mean and standard deviation of one group of channels of the
+ * input tensor for the group normalization operator.
+ *
+ * Given a tensor of shape [W, H, C, N] the mean and standard deviation tensors
+ * will have a shape of [G, N] where G = C / group.
+ *
+ * The input tensor is assumed to be a channels-packed texture tensor with the
+ * standard axis mapping. The output tensors are assumed to be contiguous buffer
+ * tensors.
+ *
+ * Algorithm:
+ * 1. Each shader invocation corresponds to one group in one batch
+ * 2. The local work group cooperatively reduces over all spatial locations (H×W)
+ *    and all channels within the group (C/group channels)
+ * 3. Uses shared memory for efficient parallel reduction
+ * 4. Main thread (local ID 0) writes the final mean and rstd to buffer
+ *
+ * Global work group size: {N, 1, 1}
+ * N is the number of elements in the tensor buffer; each thread computes one
+ * output element.
+ *
+ * Local work group size:  {1, float, 1}
+ * float should be a power of 2, recommended 64 or 128 threads. This allows
+ * efficient tree-based reduction in shared memory. Each local group will
+ * cooperate to compute the output element.
+ *
+ * Each shader invocation will compute the mean and standard deviation for one
+ * channel group in the input, and write out the corresponding result.
+ */
+void group_norm_reduce_C_packed() {
+  const int global_idx = int(gl_GlobalInvocationID.x);
+  const int local_idx = int(gl_LocalInvocationID.y);
+
+  // Calculate group dimensions
+  const int D = in_sizes.z / group;  // channels per group
+  const int HxW = in_sizes.y * in_sizes.x;  // spatial size
+  const int group_size = D * HxW;  // total elements per group
+
+  // Convert global index to (group_idx, batch_idx)
+  const ivec4 mean_tidx = bufi_to_tidx(global_idx, mean_strides, mean_dim_order);
+
+  // Initialize local sums
+  float local_sum = 0.0;
+  float local_sum_sq = 0.0;
+  int local_count = 0;
+
+  // Calculate the range of channels for this group
+  const int group_start_channel = mean_tidx.x * D;
+  const int group_end_channel = group_start_channel + D;
+
+  // Calculate the range of texels that contain channels from this group
+  const int start_texel_idx = group_start_channel / 4;
+  const int end_texel_idx = divup4(group_end_channel);
+  const int texels_in_group = end_texel_idx - start_texel_idx;
+
+  // Total texels to process across all spatial locations
+  const int total_texels = texels_in_group * HxW;
+
+  // Each thread processes a subset of texels
+  const int texels_per_thread = (total_texels + LOCAL_WORK_GROUP_SIZE - 1) / LOCAL_WORK_GROUP_SIZE;
+  const int start_texel = local_idx * texels_per_thread;
+  const int end_texel = min(start_texel + texels_per_thread, total_texels);
+
+  // Process assigned texels
+  for (int texel_idx = start_texel; texel_idx < end_texel; texel_idx++) {
+    // Convert texel index to spatial and channel coordinates
+    const int spatial_idx = texel_idx / texels_in_group;
+    const int texel_in_group = texel_idx % texels_in_group;
+
+    // Convert to spatial coordinates
+    const int w = spatial_idx % in_sizes.x;
+    const int h = spatial_idx / in_sizes.x;
+
+    // Calculate the global texel index
+    const int global_texel_idx = start_texel_idx + texel_in_group;
+
+    // Convert to texture position using default axis mapping
+    ivec3 tex_pos = ivec3(w, h, global_texel_idx);
+
+    // Adjust for batch dimension if needed
+    if (in_sizes.w > 1) {
+      // default axis mapping means channels is the batch concat dim
+      tex_pos.z += mean_tidx.y * divup4(in_sizes.z);
+    }
+
+    // Check bounds and load texel
+    if (all(lessThan(tex_pos, in_limits))) {
+      const vec4 texel_val = load_texel(t_in, tex_pos);
+
+      // Process all components of the texel that belong to this group
+      const int texel_start_channel = global_texel_idx * 4;
+      for (int comp = 0; comp < 4; comp++) {
+        const int current_channel = texel_start_channel + comp;
+
+        // Check if this component belongs to the current group
+        if (current_channel >= group_start_channel && current_channel < group_end_channel) {
+          const float val = texel_val[comp];
+          local_sum += val;
+          local_sum_sq += val * val;
+          local_count++;
+        }
+      }
+    }
+  }
+
+  // Store local results in shared memory
+  shared_sum[local_idx] = local_sum;
+  shared_sum_sq[local_idx] = local_sum_sq;
+
+  // Synchronize threads
+  memoryBarrierShared();
+  barrier();
+
+  // Perform tree-based reduction in shared memory
+  for (int stride = LOCAL_WORK_GROUP_SIZE / 2; stride > 0; stride /= 2) {
+    if (local_idx < stride) {
+      shared_sum[local_idx] += shared_sum[local_idx + stride];
+      shared_sum_sq[local_idx] += shared_sum_sq[local_idx + stride];
+    }
+    memoryBarrierShared();
+    barrier();
+  }
+
+  // Main thread writes the result
+  if (local_idx == 0 && global_idx < mean_numel) {
+    const float total_sum = shared_sum[0];
+    const float total_sum_sq = shared_sum_sq[0];
+    const float count = float(group_size);
+
+    // Calculate mean and reciprocal standard deviation
+    const float mean_val = total_sum / count;
+    const float variance = (total_sum_sq / count) - (mean_val * mean_val);
+    const float rstd_val = 1.0 / sqrt(variance + epsilon);
+
+    // Write to buffer-backed tensors
+    t_mean[global_idx] = BUF_T(mean_val);
+    t_rstd[global_idx] = BUF_T(rstd_val);
+  }
+}
+
+void main() {
+  group_norm_reduce_C_packed();
+}

backends/vulkan/runtime/graph/ops/glsl/group_norm_reduce_texture.yaml

@@ -0,0 +1,15 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+group_norm_reduce_texture:
+  parameter_names_with_default_values:
+    DTYPE: float
+  generate_variant_forall:
+    DTYPE:
+      - VALUE: half
+      - VALUE: float
+  shader_variants:
+    - NAME: group_norm_reduce_texture