[ET-VK][Ops] dequantize_per_channel shaders and impl (pytorch#12435)

# Context

We need to enable the core logic for dequantize_per_channel in the vulkan shader. This implements the shader itself and its cpp header.

TODO: add more of a description regarding the operator

# Changes

This creates an extension of the existing files for dequantize_per_channel.

Differential Revision: [D77746141](https://our.internmc.facebook.com/intern/diff/D77746141/)

Author: pytorchbot

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

@@ -42,6 +42,16 @@ $if MODE == "per_token":
     int quant_min;
     int quant_max;
   };
+$if MODE == "per_channel":
+  ${layout_declare_tensor(B, "r", "t_scale", "float", "buffer")}
+  ${layout_declare_tensor(B, "r", "t_zero_point", "int", "buffer")}
+
+  layout(push_constant) uniform restrict Block {
+    int axis;
+    int num_channels;
+    int quant_min;
+    int quant_max;
+  };
 
 ${layout_declare_ubo(B, "int", "out_numel")}
 ${layout_declare_ubo(B, "ivec4", "t_in_sizes")}
@@ -141,7 +151,7 @@ void dequantize_per_tensor() {
   t_out[out_bufi] = value;
 }
 
-#else
+#elif defined(per_token)
 
 void dequantize_per_token() {
   const int out_bufi = int(gl_GlobalInvocationID.x);
@@ -176,6 +186,45 @@ void dequantize_per_token() {
   t_out[out_bufi] = value;
 }
 
+#else // per_channel
+
+void dequantize_per_channel() {
+  const int out_bufi = int(gl_GlobalInvocationID.x);
+
+  if (out_bufi >= out_numel) {
+    return;
+  }
+
+  const ivec4 out_tidx = bufi_to_tidx(out_bufi, t_out_strides, out_dim_order);
+  const int in_bufi = tidx_to_bufi(out_tidx, t_in_strides);
+
+  IN_T qvalue = t_in[in_bufi];
+
+  // Calculate channel index based on the dequantization axis (already converted to WHCN)
+  // The axis parameter is now in WHCN coordinate system:
+  // axis 0 -> W dimension (tidx.x)
+  // axis 1 -> H dimension (tidx.y)
+  // axis 2 -> C dimension (tidx.z)
+  // axis 3 -> N dimension (tidx.w)
+  int channel_idx = 0;
+
+  if (axis == 0) {
+    channel_idx = out_tidx.x;
+  } else if (axis == 1) {
+    channel_idx = out_tidx.y;
+  } else if (axis == 2) {
+    channel_idx = out_tidx.z;
+  } else if (axis == 3) {
+    channel_idx = out_tidx.w;
+  }
+
+  channel_idx = min(channel_idx, num_channels - 1);
+
+  OUT_T value = dequantize_val(qvalue, t_scale[channel_idx], t_zero_point[channel_idx]);
+
+  t_out[out_bufi] = value;
+}
+
 #endif
 
 void main() {

backends/vulkan/runtime/graph/ops/glsl/dequantize_buffer.yaml

@@ -17,3 +17,5 @@ dequantize_buffer:
       MODE: per_tensor
     - NAME: dequantize_per_token_buffer
       MODE: per_token
+    - NAME: dequantize_per_channel_buffer
+      MODE: per_channel

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

@@ -45,6 +45,16 @@ $if MODE == "per_token":
     int quant_min;
     int quant_max;
   };
+$if MODE == "per_channel":
+  ${layout_declare_tensor(B, "r", "t_scale", "float", "buffer")}
+  ${layout_declare_tensor(B, "r", "t_zero_point", "int", "buffer")}
+
+  layout(push_constant) uniform restrict Block {
+    int axis;
+    int num_channels;
+    int quant_min;
+    int quant_max;
+  };
 
 ${layout_declare_ubo(B, "ivec3", "t_in_limits")}
 ${layout_declare_ubo(B, "ivec3", "t_out_limits")}
@@ -147,7 +157,7 @@ void dequantize_per_tensor() {
   write_texel(t_out, pos, outtex);
 }
 
-#else
+#elif defined(per_token)
 
 void dequantize_per_token() {
   const ivec3 pos = ivec3(gl_GlobalInvocationID);
@@ -189,6 +199,97 @@ void dequantize_per_token() {
   write_texel(t_out, pos, outtex);
 }
 
+#else // per_channel
+
+void dequantize_per_channel() {
+  const ivec3 pos = ivec3(gl_GlobalInvocationID);
+
+  if (any(greaterThanEqual(pos, t_in_limits))) {
+    return;
+  }
+
+  IVEC4_T intex = load_texel(t_in, pos);
+  FVEC4_T outtex;
+
+  // Calculate channel index based on the dequantization axis (already converted to WHCN)
+  // The axis parameter is now in WHCN coordinate system:
+  // axis 0 -> W dimension (pos.x)
+  // axis 1 -> H dimension (pos.y)
+  // axis 2 -> C dimension (pos.z)
+  // axis 3 -> N dimension (batch folding in texture storage)
+
+  if (axis == 0) {
+    // Width dimension - each texel component has different channel index
+    [[unroll]] for (int i = 0; i < 4; ++i) {
+      IN_T qvalue = IN_T(intex[i]);
+      int channel_idx = pos.x * 4 + i;
+      channel_idx = min(channel_idx, num_channels - 1);
+
+      float scale_val = t_scale[channel_idx];
+      int zero_point_val = t_zero_point[channel_idx];
+      OUT_T value = dequantize_val(qvalue, scale_val, zero_point_val);
+      $if OUT_DTYPE == "double":
+        outtex[i] = float(value);
+      $else:
+        outtex[i] = value;
+    }
+  } else if (axis == 1) {
+    int channel_idx = pos.y;
+    channel_idx = min(channel_idx, num_channels - 1);
+    float scale_val = t_scale[channel_idx];
+    int zero_point_val = t_zero_point[channel_idx];
+
+    [[unroll]] for (int i = 0; i < 4; ++i) {
+      IN_T qvalue = IN_T(intex[i]);
+      OUT_T value = dequantize_val(qvalue, scale_val, zero_point_val);
+      $if OUT_DTYPE == "double":
+        outtex[i] = float(value);
+      $else:
+        outtex[i] = value;
+    }
+  } else if (axis == 2) {
+    // Channel dimension - for 4D tensors, need to account for batch-channel folding
+    // The Z coordinate contains folded batch*channel information
+    // We need to extract the actual channel index from the folded dimension
+    int folded_idx = pos.z;
+    int channel_idx = folded_idx % num_channels;
+
+    float scale_val = t_scale[channel_idx];
+    int zero_point_val = t_zero_point[channel_idx];
+
+    [[unroll]] for (int i = 0; i < 4; ++i) {
+      IN_T qvalue = IN_T(intex[i]);
+      OUT_T value = dequantize_val(qvalue, scale_val, zero_point_val);
+      $if OUT_DTYPE == "double":
+        outtex[i] = float(value);
+      $else:
+        outtex[i] = value;
+    }
+  } else if (axis == 3) {
+    // Batch dimension - for 4D tensors, need to account for batch-channel folding
+    // The Z coordinate contains folded batch*channel information
+    // We need to extract the actual channel index from the folded dimension
+    int folded_idx = pos.z;
+    // In this case num_channels actually corresponds to the number of channels
+    // the C dimension N(C)HW
+    int channel_idx = folded_idx / num_channels;
+
+    float scale_val = t_scale[channel_idx];
+    int zero_point_val = t_zero_point[channel_idx];
+
+    [[unroll]] for (int i = 0; i < 4; ++i) {
+      IN_T qvalue = IN_T(intex[i]);
+      OUT_T value = dequantize_val(qvalue, scale_val, zero_point_val);
+      $if OUT_DTYPE == "double":
+        outtex[i] = float(value);
+      $else:
+        outtex[i] = value;
+    }
+  }
+
+  write_texel(t_out, pos, outtex);
+}
+
 #endif
 
 void main() {

backends/vulkan/runtime/graph/ops/glsl/dequantize_texture.yaml

@@ -17,3 +17,5 @@ dequantize_texture:
       MODE: per_tensor
     - NAME: dequantize_per_token_texture3d
       MODE: per_token
+    - NAME: dequantize_per_channel_texture3d
+      MODE: per_channel