PERF: add shortcut to Timedelta constructor

doc/source/whatsnew/v1.1.0.rst

@@ -39,7 +39,7 @@ Deprecations
 
 Performance improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
-
+- Performance improvement in :class:`Timedelta` constructor (:issue:`30543`)
 -
 -
 

pandas/_libs/tslibs/timedeltas.pyx

@@ -1208,7 +1208,12 @@ class Timedelta(_Timedelta):
                 "represent unambiguous timedelta values durations."
             )
 
-        if isinstance(value, Timedelta):
+        # GH 30543 if pd.Timedelta already passed, return it
+        # check that only value is passed
+        if (isinstance(value, Timedelta) and unit is None and
+                len(kwargs) == 0):
+            return value
+        elif isinstance(value, Timedelta):
             value = value.value
         elif isinstance(value, str):
             if len(value) > 0 and value[0] == 'P':

pandas/tests/indexes/datetimes/test_constructors.py

@@ -950,3 +950,10 @@ def test_datetimeindex_constructor_misc(self):
         )
         assert len(idx1) == len(idx2)
         assert idx1.freq == idx2.freq
+
+
+def test_timedelta_constructor_identity():
+    # Test for #30543
+    expected = pd.Timedelta(np.timedelta64(1, "s"))
+    result = pd.Timedelta(expected)
+    assert result is expected