[ET-VK] Reduced int precision for texture coordinates in conv2d_pw op, to reduce shader register pressure and slightly improve performance.

This diff reduces the precision of texture coordinates in the conv2d_pw op in Executorch Vulkan backend to reduce shader register pressure.

Differential Revision: [D64766910](https://our.internmc.facebook.com/intern/diff/D64766910/)

[ghstack-poisoned]

Author: trivedivivek

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

@@ -32,24 +32,26 @@ ${layout_declare_ubo(8, "float", "out_min", "float", "out_max")}
 
 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
+
 /*
  * 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 ivec3 gpos = ivec3(gl_GlobalInvocationID);
+  const u16vec3 gpos = u16vec3(gl_GlobalInvocationID);
 
   // Output position for TILE_SIZE = 2
   // +--------+--------+
   // | pos[0] | pos[1] |
   // +--------+--------+
   // | pos[2] | pos[3] |
   // +--------+--------+
-  ivec3 pos[TILE_SIZE * TILE_SIZE];
+  u16vec3 pos[TILE_SIZE * TILE_SIZE];
   for (int y = 0, i = 0; y < TILE_SIZE; ++y) {
     for (int x = 0; x < TILE_SIZE; ++x) {
-      pos[i] = ivec3(
+      pos[i] = u16vec3(
           gpos.x * TILE_SIZE + x, gpos.y * TILE_SIZE + y, gpos.z);
       i++;
     }
@@ -64,13 +66,13 @@ void main() {
   // 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 * TILE_SIZE];
+  u16vec2 ipos[TILE_SIZE * TILE_SIZE];
   for (int i = 0; i < TILE_SIZE * TILE_SIZE; ++i) {
-    ipos[i] = pos[i].xy * stride - padding;
+    ipos[i] = pos[i].xy * u16vec2(stride) - u16vec2(padding);
   }
 
   vec4 sum[TILE_SIZE * TILE_SIZE];
-  sum[0] = texelFetch(t_bias, ivec2(gpos.z, 0), 0);
+  sum[0] = texelFetch(t_bias, u16vec2(gpos.z, 0), 0);
   for (int i = 1; i < TILE_SIZE * TILE_SIZE; ++i) {
     sum[i] = sum[0];
   }
@@ -81,13 +83,13 @@ void main() {
     // channel (IC) dim is along the x-axis, and the batch (OC) dim is along
     // the z-axis.
     vec4 in_tex[TILE_SIZE * TILE_SIZE];
-    const vec4 ktex_0 = texelFetch(t_kernel, ivec2(z + 0, gpos.z), 0);
-    const vec4 ktex_1 = texelFetch(t_kernel, ivec2(z + 1, gpos.z), 0);
-    const vec4 ktex_2 = texelFetch(t_kernel, ivec2(z + 2, gpos.z), 0);
-    const vec4 ktex_3 = texelFetch(t_kernel, ivec2(z + 3, gpos.z), 0);
+    const vec4 ktex_0 = texelFetch(t_kernel, u16vec2(z + 0, gpos.z), 0);
+    const vec4 ktex_1 = texelFetch(t_kernel, u16vec2(z + 1, gpos.z), 0);
+    const vec4 ktex_2 = texelFetch(t_kernel, u16vec2(z + 2, gpos.z), 0);
+    const vec4 ktex_3 = texelFetch(t_kernel, u16vec2(z + 3, gpos.z), 0);
 
     for (int i = 0; i < TILE_SIZE * TILE_SIZE; ++i) {
-      in_tex[i] = texelFetch(t_in, ivec3(ipos[i], z4), 0);
+      in_tex[i] = texelFetch(t_in, u16vec3(ipos[i], z4), 0);
     }
 
     for (int i = 0; i < TILE_SIZE * TILE_SIZE; ++i) {