Update slice

Signed-off-by: Justin Chu <justinchuby@users.noreply.github.com>

Author: justinchuby

onnxscript/optimizer/_constant_folding.py

@@ -546,6 +546,20 @@ def squeeze(node: ir.Node, op, state: OptimizerState) -> ReturnValue:
     return _propagate_shape_value(node, op, state)
 
 
+@register("Slice")
+def slice_op(node: ir.Node, op, state: OptimizerState) -> ReturnValue:
+    """Replace Slice with Identity when output shape matches input shape."""
+    input = _get_input(node, 0)
+    if input is None or input.shape is None:
+        return None
+    output = _get_output(node, 0)
+    if output is None or output.shape is None:
+        return None
+    if _same_shape(input.shape, output.shape):
+        return op.Identity(input)
+    return None
+
+
 @register("Cast")
 def cast(node: ir.Node, op, state: OptimizerState) -> ReturnValue:
     input = _get_input(node, 0)