gh-130704: Strength reduce LOAD_FAST{_LOAD_FAST} (#130708)

Optimize `LOAD_FAST` opcodes into faster versions that load borrowed references onto the operand stack when we can prove that the lifetime of the local outlives the lifetime of the temporary that is loaded onto the stack.

Lib/test/test_frame.py

@@ -597,6 +597,22 @@ class TestFrameLocals(unittest.TestCase):
         with self.assertRaises(TypeError):
             FrameLocalsProxy(frame=sys._getframe())  # no keyword arguments
 
+    def test_overwrite_locals(self):
+        # Verify we do not crash if we overwrite a local passed as an argument
+        # from an ancestor in the call stack.
+        def f():
+            xs = [1, 2, 3]
+            ys = [4, 5, 6]
+            return g(xs)
+
+        def g(xs):
+            f = sys._getframe()
+            f.f_back.f_locals["xs"] = None
+            f.f_back.f_locals["ys"] = None
+            return xs[1]
+
+        self.assertEqual(f(), 2)
+
 
 class FrameLocalsProxyMappingTests(mapping_tests.TestHashMappingProtocol):
     """Test that FrameLocalsProxy behaves like a Mapping (with exceptions)"""