[ET-VK] New Implementation of `permute' operator (pytorch#11971)

## Changes

* Introduce `permute_buffer.glsl` and `permute_texture.glsl` compute shader templates to implement the permute operator

## Motivation

The existing implementation of permute produced incorrect outputs for width packed textures. Furthermore, there was no buffer implementation for the permute operator.

My goal with this diff is to introduce a more flexible implementation of permute that could work for any tensor representation.

## Performance impact

None expected.

Differential Revision: [D76483755](https://our.internmc.facebook.com/intern/diff/D76483755/)

Author: pytorchbot

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

@@ -0,0 +1,72 @@
+/*
+ * 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
+
+#define PRECISION ${PRECISION}
+
+#define VEC4_T ${texel_type(DTYPE)}
+#define T ${buffer_scalar_type(DTYPE)}
+
+${define_active_storage_type("buffer")}
+${define_required_extensions(DTYPE)}
+
+layout(std430) buffer;
+
+#include "indexing_utils.h"
+
+${layout_declare_tensor(B, "w", "t_out", DTYPE, "buffer")}
+${layout_declare_tensor(B, "r", "t_in", DTYPE, "buffer")}
+
+${layout_declare_ubo(B, "ivec4", "in_sizes")}
+${layout_declare_ubo(B, "ivec4", "out_strides")}
+${layout_declare_ubo(B, "int", "out_numel")}
+
+layout(push_constant) uniform restrict Block {
+  ivec4 in_strides;
+  ivec4 permute_dims; // Permutation mapping: permute_dims[i] = j means output dim i comes from input dim j
+};
+
+${layout_declare_spec_const(C, "int", "out_layout", "DEFAULT_LAYOUT")}
+${layout_declare_spec_const(C, "int", "in_layout", "DEFAULT_LAYOUT")}
+
+const lowp ivec4 out_dim_order = unhash_dim_order(out_layout);
+
+layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
+
+// Convert output tensor index to input tensor index based on permutation
+ivec4 out_tidx_to_in_tidx(const ivec4 out_tidx) {
+  ivec4 in_tidx;
+
+  // Apply the permutation mapping: in_tidx[permute_dims[i]] = out_tidx[i]
+  in_tidx[permute_dims.x] = out_tidx.x;
+  in_tidx[permute_dims.y] = out_tidx.y;
+  in_tidx[permute_dims.z] = out_tidx.z;
+  in_tidx[permute_dims.w] = out_tidx.w;
+
+  return in_tidx;
+}
+
+void main() {
+  const int out_bufi = ivec3(gl_GlobalInvocationID).x;
+  if (out_bufi >= out_numel) {
+    return;
+  }
+
+  // Convert buffer index to tensor index for output
+  const ivec4 out_tidx = bufi_to_tidx(out_bufi, out_strides, out_dim_order);
+
+  // Convert output tensor index to input tensor index using permutation
+  const ivec4 in_tidx = out_tidx_to_in_tidx(out_tidx);
+
+  // Convert input tensor index back to buffer index
+  const int in_bufi = tidx_to_bufi(in_tidx, in_strides);
+
+  // Copy data from input to output
+  t_out[out_bufi] = t_in[in_bufi];
+}

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

@@ -1,12 +1,10 @@
-permute:
+permute_buffer:
   parameter_names_with_default_values:
     DTYPE: float
-    NDIM: 3
-    STORAGE: texture3d
   generate_variant_forall:
     DTYPE:
       - VALUE: half
       - VALUE: float
       - VALUE: int32
   shader_variants:
-    - NAME: permute
+    - NAME: permute_buffer

backends/vulkan/runtime/graph/ops/glsl/permute.yaml renamed to backends/vulkan/runtime/graph/ops/glsl/permute_buffer.yaml

@@ -0,0 +1,103 @@
+/*
+ * 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
+
+#define PRECISION ${PRECISION}
+
+#define VEC4_T ${texel_type(DTYPE)}
+#define T ${buffer_scalar_type(DTYPE)}
+
+${define_active_storage_type("texture3d")}
+${define_required_extensions(DTYPE)}
+
+layout(std430) buffer;
+
+#include "indexing_utils.h"
+
+${layout_declare_tensor(B, "w", "t_out", DTYPE, "texture3d")}
+${layout_declare_tensor(B, "r", "t_in", DTYPE, "texture3d")}
+
+layout(push_constant) uniform restrict Block {
+  ivec4 out_sizes;
+  ivec4 in_sizes;
+  ivec4 permute_dims; // Permutation mapping: permute_dims[i] = j means output dim i comes from input dim j
+};
+
+${layout_declare_spec_const(C, "int", "out_layout", "DEFAULT_LAYOUT")}
+const lowp ivec4 out_axis_map = unhash_axis_map(out_layout);
+const lowp int out_packed_dim = unhash_packed_dim(out_layout);
+
+${layout_declare_spec_const(C, "int", "in_layout", "DEFAULT_LAYOUT")}
+const lowp ivec4 in_axis_map = unhash_axis_map(in_layout);
+const lowp int in_packed_dim = unhash_packed_dim(in_layout);
+
+layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
+
+// Convert output tensor index to input tensor index based on permutation
+ivec4 out_tidx_to_in_tidx(const ivec4 out_tidx) {
+  ivec4 in_tidx;
+
+  // Apply the permutation mapping: in_tidx[permute_dims[i]] = out_tidx[i]
+  in_tidx[permute_dims.x] = out_tidx.x;
+  in_tidx[permute_dims.y] = out_tidx.y;
+  in_tidx[permute_dims.z] = out_tidx.z;
+  in_tidx[permute_dims.w] = out_tidx.w;
+
+  return in_tidx;
+}
+
+// Check if we can use the fast path where texels from the input tensor can be
+// copied directly into the output tensor. This occurs when the packed dimension
+// is preserved in the permutation, i.e. reading a texel from the output tensor
+// produces 4 texels along the same dimension as reading a texel from the input
+// tensor.
+bool can_use_fast_path() {
+  // Fast path is possible when the packed dimension is preserved in the permutation
+  // This means permute_dims[out_packed_dim] == in_packed_dim
+  return permute_dims[out_packed_dim] == in_packed_dim;
+}
+
+void main() {
+  const ivec3 lpos = ivec3(gl_GlobalInvocationID);
+  ivec4 out_tidx = lpos_to_tidx(lpos, out_sizes, out_axis_map.w, out_packed_dim);
+
+  if (any(greaterThanEqual(out_tidx, out_sizes))) {
+    return;
+  }
+
+  if (can_use_fast_path()) {
+    // Fast path: packed dimension is preserved, so we can copy texels directly
+    ivec4 in_tidx = out_tidx_to_in_tidx(out_tidx);
+    ivec3 in_pos = tidx_to_pos(in_tidx, in_sizes, in_axis_map, in_packed_dim);
+    VEC4_T in_texel = VEC4_T(load_texel(t_in, in_pos));
+
+    write_texel_lpos(t_out, lpos, in_texel, out_axis_map);
+  }
+  else {
+    // Slow path: packed dimension is not preserved, so each element of the
+    // output texel may be "sourced" from a different texel in the input tensor.
+    // Therefore each output texel element is processed individually.
+    VEC4_T out_texel = VEC4_T(0);
+
+    for (int texel_i = 0; texel_i < 4; ++texel_i) {
+      ivec4 in_tidx = out_tidx_to_in_tidx(out_tidx);
+      ivec3 in_pos = tidx_to_pos(in_tidx, in_sizes, in_axis_map, in_packed_dim);
+      int element_idx = in_tidx[in_packed_dim] % 4;
+
+      VEC4_T in_texel = VEC4_T(load_texel(t_in, in_pos));
+      T selected_value = T(in_texel[element_idx]);
+
+      out_texel[texel_i] = selected_value;
+
+      out_tidx[out_packed_dim]++;
+    }
+
+    write_texel_lpos(t_out, lpos, out_texel, out_axis_map);
+  }
+}

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

@@ -0,0 +1,10 @@
+permute_texture:
+  parameter_names_with_default_values:
+    DTYPE: float
+  generate_variant_forall:
+    DTYPE:
+      - VALUE: half
+      - VALUE: float
+      - VALUE: int32
+  shader_variants:
+    - NAME: permute_texture3d