WIP Adding WB to object.c

- [ ] Line 1176: if(Py_CHECKWRITE(v)){
- [ ] Line 1193: if(Py_CHECKWRITE(v)){
- [x] Line 1639: if(!Py_CHECKWRITE(obj)){

The first two cases are in `PyObject_SetAttr`.

I believe that `PyObject_SetAttr` falls out for free with the default
`tp_setattro` implementation which simply calls `PyObjectGenericSetAttr`
which in turn always ends up in `dictobject.c` -- unless we hit line
1567 which uses `tp_descr_set`, overloading of `__set__`.

However, `__set__` descriptors' behaviour should fall out for free as
they will eventually hit a "normal" store which should be trapped by
the write barrier.

The normal `tp_setattro` implementation is changed by `__setattr__`
being overridden by user. We should expect things to fall out for free
in this case since that code will eventually hit a "normal" store.

Exceptions: unless the implementation of `__setattr__` or `__set__` is
written in C. **Question: how to handle this case?**

The third and last case is a call to `PyObject_GenericSetDict` which
is the setter for `o.__dict__ = v`. In this case, we need an add ref
on the v and a remove ref on the old value of `o.__dict__`.  This has
been implemented. However, I have so far been unable to trigger this
code. `o.__dict__ = v` runs `subtype_setdict` which I have extended
in a similar fashion.

I have potentially discovered a couple of places missing a CHECKWRITE
which I will report on in an issue.

Author: TobiasWrigstad

Include/internal/pycore_regions.h

@@ -39,6 +39,8 @@ PyObject* _Py_ResetInvariant(void);
 #define Py_ResetInvariant() _Py_ResetInvariant()
 
 // Invariant placeholder
+bool _Pyrona_RemoveReference(PyObject* target, PyObject* old_ref);
+#define Pyrona_REMOVEREFERENCE(a, b) _Pyrona_RemoveReference(a, b)
 bool _Pyrona_AddReference(PyObject* target, PyObject* new_ref);
 #define Pyrona_ADDREFERENCE(a, b) _Pyrona_AddReference(a, b)
 // Helper macros to count the number of arguments

Objects/object.c

@@ -1667,8 +1667,12 @@ PyObject_GenericSetDict(PyObject *obj, PyObject *value, void *context)
                      "not a '%.200s'", Py_TYPE(value)->tp_name);
         return -1;
     }
-    Py_XSETREF(*dictptr, Py_NewRef(value));
-    return 0;
+    if (_Pyrona_AddReference(obj, value)) {
+        Py_XSETREF(*dictptr, Py_NewRef(value));
+        return 0;
+    } else {
+        return -1;
+    }
 }
 
 

Objects/regions.c

@@ -1297,6 +1297,13 @@ static const char *get_region_name(PyObject* obj) {
 }
 
 // TODO replace with write barrier code
+bool _Pyrona_RemoveReference(PyObject *tgt, PyObject *old_ref) {
+#ifndef NDEBUG
+        _Py_VPYDBG("Removed %p --> %p (owner: '%s')\n", tgt, old_ref, get_region_name(tgt));
+#endif
+    return true; // TODO: implement
+}
+
 bool _Pyrona_AddReference(PyObject *tgt, PyObject *new_ref) {
     if (Py_REGION(tgt) == Py_REGION(new_ref)) {
         // Nothing to do -- intra-region references are always permitted

Objects/typeobject.c

@@ -3,6 +3,7 @@
 #include "Python.h"
 #include "pycore_call.h"
 #include "pycore_code.h"          // CO_FAST_FREE
+#include "pycore_regions.h"
 #include "pycore_symtable.h"      // _Py_Mangle()
 #include "pycore_dict.h"          // _PyDict_KeysSize()
 #include "pycore_initconfig.h"    // _PyStatus_OK()
@@ -2940,8 +2941,15 @@ subtype_setdict(PyObject *obj, PyObject *value, void *context)
                      "not a '%.200s'", Py_TYPE(value)->tp_name);
         return -1;
     }
-    Py_XSETREF(*dictptr, Py_XNewRef(value));
-    return 0;
+    if (_Pyrona_AddReference(obj, value)) {
+        if (*dictptr) {
+            _Pyrona_RemoveReference(obj, *dictptr);
+        }
+        Py_XSETREF(*dictptr, Py_XNewRef(value));
+        return 0;
+    } else {
+        return -1;
+    }
 }
 
 static PyObject *