More optimizations

Author: tomasr8

Lib/test/test_capi/test_opt.py

@@ -1832,6 +1832,27 @@ def testfunc(n):
         self.assertIn("_BINARY_OP_ADD_UNICODE", uops)
         self.assertNotIn("_GUARD_NOS_UNICODE", uops)
 
+    def test_call_str_1_result_is_const_for_str_input(self):
+        # Test a special case where the argument of str(arg)
+        # is known to be a string. The information about the
+        # argument being a string should be propagated to the
+        # result of str(arg).
+        def testfunc(n):
+            x = 0
+            for _ in range(n):
+                y = str('foo')  # string argument
+                if y:           # _TO_BOOL_STR + _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_STR_1", uops)
+        self.assertNotIn("_TO_BOOL_STR", uops)
+        self.assertNotIn("_GUARD_IS_TRUE_POP", uops)
+
 
 def global_identity(x):
     return x

Python/optimizer_bytecodes.c

@@ -855,8 +855,15 @@ dummy_func(void) {
         }
     }
 
-    op(_CALL_STR_1, (unused, unused, unused -- res)) {
-        res = sym_new_type(ctx, &PyUnicode_Type);
+    op(_CALL_STR_1, (unused, unused, arg -- res)) {
+        if (sym_matches_type(arg, &PyUnicode_Type)) {
+            // e.g. str('foo') or str(foo) where foo is known to be a string
+            PyObject *value = sym_get_const(ctx, arg);
+            res = sym_new_const(ctx, value);
+        }
+        else {
+            res = sym_new_type(ctx, &PyUnicode_Type);
+        }
     }
 
     op(_GUARD_IS_TRUE_POP, (flag -- )) {