Fix panic and add test for it

Author: saulshanabrook

Lib/test/test_capi/test_opt.py

@@ -1430,6 +1430,27 @@ class Foo:
         Foo.attr = 0
         self.assertFalse(ex.is_valid())
 
+    def test_type_version_doesnt_segfault(self):
+        """
+        Tests that setting a type version doesn't cause a segfault when later looking at the stack.
+        """
+
+        # Minimized from mdp.py benchmark
+
+        class A:
+            def __init__(self):
+                self.attr = {}
+
+            def method(self, arg):
+                self.attr[arg] = None
+
+        def fn(a):
+            for _ in range(100):
+                (_ for _ in [])
+                (_ for _ in [a.method(None)])
+
+        fn(A())
+
 
 if __name__ == "__main__":
     unittest.main()

Python/optimizer_bytecodes.c

@@ -588,7 +588,7 @@ dummy_func(void) {
         // Can determine statically, so we interleave the new locals
         // and make the current stack the new locals.
         // This also sets up for true call inlining.
-        if (sym_is_null(self_or_null) || sym_is_not_null(self_or_null)) {
+        if (sym_is_null(self_or_null)) {
             localsplus_start = args;
             n_locals_already_filled = argcount;
         }