[ET-VK] Rearranging code in permute op shader to reduce heavy math op…

…s and improve performance. (#7095)

Pull Request resolved: #7014

The diff rearranges Permute op shader code in executorch vulkan backend to reduce heavy math operations and improve performance. The change also include adding an extension to support explicit arithmetic types and changing the data type of the position variable to u16vec3.
ghstack-source-id: 255546339
@exported-using-ghexport

Differential Revision: [D66174765](https://our.internmc.facebook.com/intern/diff/D66174765/)

Co-authored-by: Vivek Trivedi <[email protected]>

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

@@ -36,8 +36,10 @@ layout(set = 0, binding = 4) uniform PRECISION restrict Block {
 
 layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
 
+#extension GL_EXT_shader_explicit_arithmetic_types_int16 : require
+
 void main() {
-  const ivec3 pos = ivec3(gl_GlobalInvocationID);
+  const u16vec3 pos = u16vec3(gl_GlobalInvocationID);
 
   if (any(greaterThanEqual(pos, out_limits))) {
     return;
@@ -46,28 +48,34 @@ void main() {
   const int out_channel_4up = int(ch_info.x);
   const int in_channel_4up = int(ch_info.y);
   const int out_batch = int(sizes[3]);
-  const int max_dst_index = out_batch * out_channel_4up;
   VEC4_T outval = VEC4_T(0.0);
+  ivec4 v = ivec4(0); // holds b,c,h,w
+
+  v[out_ndims[2]] = pos.y;
+  v[out_ndims[3]] = pos.x;
+
+  const int dst_index = pos.z << 2;
+  int dst_out_index = dst_index / out_channel_4up;
+  int dst_out_lane = dst_index % out_channel_4up;
 
-  for (int j = 0; j < 4; ++j) {
-    int dst_index = pos.z * 4 + j;
-    if (dst_index >= max_dst_index) {
+  for (int j = 0; j < 4; ++j, ++dst_out_lane) {
+    if (dst_out_index >= out_batch) {
       // out of range
       break;
     }
 
-    ivec4 v = ivec4(0); // holds b,c,h,w
-    v[out_ndims[0]] = dst_index / out_channel_4up;
-    v[out_ndims[1]] = dst_index % out_channel_4up;
-    v[out_ndims[2]] = pos.y;
-    v[out_ndims[3]] = pos.x;
+    if (dst_out_lane == out_channel_4up) {
+      dst_out_lane = 0;
+      dst_out_index++;
+    }
+
+    v[out_ndims[0]] = dst_out_index;
+    v[out_ndims[1]] = dst_out_lane;
 
     int src_index = v[0] * in_channel_4up + v[1];
-    int w = v[3];
-    int h = v[2];
 
-    VEC4_T inval = VEC4_T(texelFetch(image_in, ivec3(w, h, src_index / 4), 0));
-    outval[j] = inval[src_index % 4];
+    VEC4_T inval = VEC4_T(texelFetch(image_in, u16vec3(v[3], v[2], src_index >> 2), 0));
+    outval[j] = inval[src_index & 0x3];
   }
 
   imageStore(image_out, pos, outval);