[torchlib] Mark add/sub as trace_only (#1840)

Simplify implementation

onnxscript/function_libs/torch_lib/ops/core.py

@@ -1,7 +1,5 @@
-# --------------------------------------------------------------------------
-# Copyright (c) Microsoft Corporation. All rights reserved.
+# Copyright (c) Microsoft Corporation.
 # Licensed under the MIT License.
-# --------------------------------------------------------------------------
 # mypy: disable-error-code="misc,arg-type,type-arg,valid-type,assignment,return-value"
 """torch.ops.aten operators under the `core` module.
 
@@ -167,12 +165,13 @@ def aten_acosh(self: TFloat) -> TFloat:
     return op.Acosh(self)
 
 
-@torch_op(("aten::add.Tensor", "aten::add.Scalar", "_operator::add"))
+@torch_op(("aten::add.Tensor", "aten::add.Scalar", "_operator::add"), trace_only=True)
 def aten_add(self: TReal, other: TReal, alpha: float = 1.0) -> TReal:
     """add.Tensor(Tensor self, Tensor other, *, Scalar alpha=1) -> Tensor"""
     # TODO(microsoft/onnxruntime#15977): Improve fp16 precision
-    alpha = op.CastLike(alpha, other)
-    other = op.Mul(other, alpha)
+    if alpha != 1.0:
+        alpha = op.CastLike(alpha, other)
+        other = op.Mul(other, alpha)
     return op.Add(self, other)
 
 
@@ -8112,13 +8111,14 @@ def aten_stft(
         "aten::subtract.Tensor",
         "aten::subtract.Scalar",
         "_operator::sub",
-    )
+    ),
+    trace_only=True,
 )
 def aten_sub(self: TReal, other: TReal, alpha: float = 1.0) -> TReal:
     """sub.Tensor(Tensor self, Tensor other, *, Scalar alpha=1) -> Tensor"""
-    alpha = op.CastLike(alpha, other)
-    other = op.Mul(other, alpha)
-
+    if alpha != 1.0:
+        alpha = op.CastLike(alpha, other)
+        other = op.Mul(other, alpha)
     return op.Sub(self, other)