[ET-VK] Remove the use of shared memory in conv2d pw to improve perf.

This diff removes the use of shared memory in the conv2d pw (pointwise) operation to improve performance.

Differential Revision: [D75316188](https://our.internmc.facebook.com/intern/diff/D75316188/)

[ghstack-poisoned]

Author: trivedivivek

backends/vulkan/runtime/graph/ops/glsl/conv2d_pw.glsl

@@ -14,7 +14,6 @@
 
 #define TILE_SIZE_X ${TILE_SIZE_X}
 #define TILE_SIZE_Y ${TILE_SIZE_Y}
-#define LOCAL_WG_SIZE 64
 
 #define op(X, A, B) ${OPERATOR}
 
@@ -39,53 +38,46 @@ layout(push_constant) uniform restrict Block {
 
 layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
 
-// For performance improvement, reduce register usage by caching positions in shared memory.
-// Offset index by 1 every 16 points to avoid bank access conflict.
-#define offset_pos_index(index) (index + ((index) >> 4))
-shared ivec3 pos_shared[offset_pos_index(LOCAL_WG_SIZE * TILE_SIZE_X * TILE_SIZE_Y)];
-
 /*
  * Computes a 2D pointwise convolution of an NxN output tile. Calculating an
  * output tile for pointwise convolution is more efficient because the kernel
  * size is only 1x1, making it easier to re-use loaded texels from t_kernel.
  */
 void main() {
   const ivec2 out_limits_scaled = (out_limits.xy + ivec2(TILE_SIZE_X - 1, TILE_SIZE_Y - 1)) / ivec2(TILE_SIZE_X, TILE_SIZE_Y);
-  const uint shared_mem_stride = LOCAL_WG_SIZE;
 
   const uint div_by_x = gl_GlobalInvocationID.x / out_limits_scaled.x;
   const ivec3 gpos = ivec3(
     gl_GlobalInvocationID.x % out_limits_scaled.x,
     div_by_x % out_limits_scaled.y,
     div_by_x / out_limits_scaled.y);
 
+  // If the top left position is out of bounds, then this invocation will have
+  // no work to do.
+  if (gpos.z >= out_limits.z) {
+    return;
+  }
+
   // Output position for TILE_SIZE = 2
   // +--------+--------+
   // | pos[0] | pos[1] |
   // +--------+--------+
   // | pos[2] | pos[3] |
   // +--------+--------+
-  ivec2 pos[TILE_SIZE_X * TILE_SIZE_Y];
+  ivec3 pos[TILE_SIZE_X * TILE_SIZE_Y];
   for (int y = 0, i = 0; y < TILE_SIZE_Y; ++y) {
     for (int x = 0; x < TILE_SIZE_X; ++x) {
-      pos[i] = ivec2(gpos.x * TILE_SIZE_X + x, gpos.y * TILE_SIZE_Y + y);
-      pos_shared[offset_pos_index((shared_mem_stride * i) + gl_LocalInvocationIndex)] = ivec3(pos[i], gpos.z);
+      pos[i] = ivec3(gpos.x * TILE_SIZE_X + x, gpos.y * TILE_SIZE_Y + y, gpos.z);
       i++;
     }
   }
 
-  // If the top left position is out of bounds, then this invocation will have
-  // no work to do.
-  if (gpos.z >= out_limits.z) {
-    return;
-  }
-
   // Compute the index of the input texture that needs to be loaded for each
   // output position. Note that negative indices can be produced indicating that
   // the top-left element is in a region added by padding.
   ivec2 ipos[TILE_SIZE_X * TILE_SIZE_Y];
   for (int i = 0; i < TILE_SIZE_X * TILE_SIZE_Y; ++i) {
-    ipos[i] = pos[i] * stride - padding;
+    ipos[i] = pos[i].xy * stride - padding;
   }
 
   // Final output array where each element is a tensor value.
@@ -171,10 +163,8 @@ void main() {
   }
 
   for (int i = 0; i < TILE_SIZE_X * TILE_SIZE_Y; ++i) {
-    const uint index = (shared_mem_stride * i) + gl_LocalInvocationIndex;
-    const ivec3 pos = pos_shared[offset_pos_index(index)];
-    if (all(lessThan(pos, out_limits.xyz))) {
-      imageStore(t_out, pos, op(vec4(sum[i * 4], sum[i * 4 + 1], sum[i * 4 + 2], sum[i * 4 + 3]), out_min, out_max));
+    if (all(lessThan(pos[i], out_limits.xyz))) {
+      imageStore(t_out, pos[i], op(vec4(sum[i * 4], sum[i * 4 + 1], sum[i * 4 + 2], sum[i * 4 + 3]), out_min, out_max));
     }
   }
 }