gh-115999: Specialize `LOAD_SUPER_ATTR` in free-threaded builds (gh-127128)

Use existing helpers to atomically modify the bytecode.  Add unit tests
to ensure specializing is happening as expected.  Add test_specialize.py
that can be used with ThreadSanitizer to detect data races.  
Fix thread safety issue with cell_set_contents().

1 files changed, 5 insertions, 14 deletions

diff --git a/Python/specialize.c b/Python/specialize.c
index ba13b02..0fe4e79 100644
--- a/Python/specialize.c
+++ b/Python/specialize.c
@@ -794,9 +794,8 @@ _Py_Specialize_LoadSuperAttr(_PyStackRef global_super_st, _PyStackRef cls_st, _P
     PyObject *global_super = PyStackRef_AsPyObjectBorrow(global_super_st);
     PyObject *cls = PyStackRef_AsPyObjectBorrow(cls_st);
 
-    assert(ENABLE_SPECIALIZATION);
+    assert(ENABLE_SPECIALIZATION_FT);
     assert(_PyOpcode_Caches[LOAD_SUPER_ATTR] == INLINE_CACHE_ENTRIES_LOAD_SUPER_ATTR);
-    _PySuperAttrCache *cache = (_PySuperAttrCache *)(instr + 1);
     if (global_super != (PyObject *)&PySuper_Type) {
         SPECIALIZATION_FAIL(LOAD_SUPER_ATTR, SPEC_FAIL_SUPER_SHADOWED);
         goto fail;
@@ -805,19 +804,11 @@ _Py_Specialize_LoadSuperAttr(_PyStackRef global_super_st, _PyStackRef cls_st, _P
         SPECIALIZATION_FAIL(LOAD_SUPER_ATTR, SPEC_FAIL_SUPER_BAD_CLASS);
         goto fail;
     }
-    instr->op.code = load_method ? LOAD_SUPER_ATTR_METHOD : LOAD_SUPER_ATTR_ATTR;
-    goto success;
-
-fail:
-    STAT_INC(LOAD_SUPER_ATTR, failure);
-    assert(!PyErr_Occurred());
-    instr->op.code = LOAD_SUPER_ATTR;
-    cache->counter = adaptive_counter_backoff(cache->counter);
+    uint8_t load_code = load_method ? LOAD_SUPER_ATTR_METHOD : LOAD_SUPER_ATTR_ATTR;
+    specialize(instr, load_code);
     return;
-success:
-    STAT_INC(LOAD_SUPER_ATTR, success);
-    assert(!PyErr_Occurred());
-    cache->counter = adaptive_counter_cooldown();
+fail:
+    unspecialize(instr);
 }
 
 typedef enum {