Adds mode constant to Pad

We drop the check on the number of inputs. We could re-introduce it but it would need to be different for the supported modes.

Co-authored-by: Oleksiy <[email protected]>

Author: dvdsk

candle-onnx/src/eval.rs

@@ -1146,13 +1146,6 @@ fn simple_eval_(
                 let mode = get_attr_opt(node, "mode")?.unwrap_or("constant");
                 let data = get(&node.input[0])?;
                 let pads = get(&node.input[1])?;
-                if node.input.len() > 2 {
-                    bail!(
-                        "unsupported number of inputs {} for Pad node {:?}, expected 2",
-                        node.input.len(),
-                        node.name
-                    );
-                }
                 if pads.rank() != 1 {
                     bail!("Pad expects 'pads' input to be 1D vector: {pads:?}");
                 }
@@ -1189,6 +1182,34 @@ fn simple_eval_(
 
                         values.insert(node.output[0].clone(), out);
                     }
+                    "constant" => {
+                        let value = if node.input.len() > 2 {
+                            get(&node.input[2])?.to_vec0::<f32>()?
+                        } else {
+                            0.0
+                        };
+
+                        let mut out = data.clone();
+                        for (axis, (pad_pre, pad_post)) in
+                            pads_pre.iter().zip(pads_post).enumerate()
+                        {
+                            if *pad_pre == 0 && *pad_post == 0 {
+                                continue;
+                            }
+
+                            let mut new_dims = out.dims().to_vec();
+                            new_dims[axis] += (*pad_pre + *pad_post) as usize;
+
+                            out = Tensor::full(value, new_dims, out.device())?.slice_scatter(
+                                &out,
+                                axis,
+                                *pad_pre as usize,
+                            )?;
+                        }
+
+                        values.insert(node.output[0].clone(), out);
+                    }
+
                     _ => bail!(
                         "unsupported 'mode' value {mode:?} for Pad node {:?}",
                         node.name