[ET-VK] Minor improvement to permute op.

This change reduces the complexity of boundary comparison in permute op to improve speed.

Differential Revision: [D72866962](https://our.internmc.facebook.com/intern/diff/D72866962/)

ghstack-source-id: 277629582
Pull Request resolved: #10117

Author: trivedivivek

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

@@ -31,6 +31,8 @@ layout(push_constant) uniform PRECISION restrict Block {
 layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
 layout(constant_id = 3) const int packed_dim = C_DIM;
 
+#extension GL_EXT_control_flow_attributes : require
+
 void main() {
   ivec3 pos = ivec3(gl_GlobalInvocationID);
 
@@ -54,11 +56,16 @@ void main() {
   in_bchw_pos[out_ndims[2]] = pos.y;
   in_bchw_pos[out_ndims[3]] = pos.x;
 
-  for (int j = 0; j < 4; ++j) {
+  const int in_packed_dim_size = in_sizes[3 - out_ndims[in_packed_dim_bchw_index]];
+
+  [[unroll]] for (int j = 0, bchw_index = in_bchw_pos[out_ndims[in_packed_dim_bchw_index]]; j < 4; ++j, ++bchw_index) {
     // terminate the loop if trying to access input texture out of bounds
-    if (any(greaterThanEqual(in_bchw_pos.wzyx, in_sizes.xyzw))) {
+    if (bchw_index >= in_packed_dim_size) {
       break;
     }
+    // go to position in the input, that is mapped to the packed dim in the output
+    in_bchw_pos[out_ndims[in_packed_dim_bchw_index]] = bchw_index;
+
     ivec3 fetch_pos;
 
     fetch_pos.xy = in_bchw_pos.wz;
@@ -74,9 +81,6 @@ void main() {
     // fetch input texel
     VEC4_T inval = VEC4_T(load_texel(t_in, fetch_pos));
     outval[j] = inval[in_packed_dim_lane_index];
-
-    // go to next position in the input, that is mapped to the packed dim in the output
-    in_bchw_pos[out_ndims[in_packed_dim_bchw_index]]++;
   }
 
   pos[packed_dim] = int(gl_GlobalInvocationID[packed_dim]);