Optimize case when input is already a tuple

Author: tomasr8

Lib/test/test_capi/test_opt.py

@@ -1832,6 +1832,29 @@ def testfunc(n):
         self.assertIn("_BINARY_OP_SUBSCR_TUPLE_INT", uops)
         self.assertNotIn("_GUARD_NOS_TUPLE", uops)
 
+    def test_call_tuple_1_result_propagates_for_tuple_input(self):
+        # Test a special case where the argument of tuple(arg)
+        # is known to be a tuple. The information about the
+        # argument being a tuple should be propagated to the
+        # result of tuple(arg).
+        def testfunc(n):
+            x = 0
+            for _ in range(n):
+                y = tuple((1, 2))  # tuple argument
+                a, _ = y           # _UNPACK_SEQUENCE_TWO_TUPLE
+                if a == 1:         # _COMPARE_OP_INT + _GUARD_IS_TRUE_POP are removed
+                    x += 1
+            return x
+
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+        self.assertIn("_CALL_TUPLE_1", uops)
+        self.assertIn("_UNPACK_SEQUENCE_TWO_TUPLE", uops)
+        self.assertNotIn("_COMPARE_OP_INT", uops)
+        self.assertNotIn("_GUARD_IS_TRUE_POP", uops)
+
 
 def global_identity(x):
     return x

Python/optimizer_bytecodes.c

@@ -958,7 +958,13 @@ dummy_func(void) {
     }
 
     op(_CALL_TUPLE_1, (callable, null, arg -- res)) {
-        res = sym_new_type(ctx, &PyTuple_Type);
+        if (sym_matches_type(arg, &PyTuple_Type)) {
+            // e.g. tuple((1, 2)) or tuple(foo) where foo is known to be a tuple
+            res = arg;
+        }
+        else {
+            res = sym_new_type(ctx, &PyTuple_Type);
+        }
     }
 
     op(_GUARD_TOS_LIST, (tos -- tos)) {