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[DRAFT] gh-105059: C99 avoids PyObject.ob_refcnt union #105767

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[DRAFT] gh-105059: C99 avoids PyObject.ob_refcnt union #105767

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57 changes: 48 additions & 9 deletions Include/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,13 @@ whose size is determined when the object is allocated.
# error Py_LIMITED_API is incompatible with Py_TRACE_REFS
#endif

#if (defined __STDC_VERSION__ && __STDC_VERSION__ >= 201112L) || defined(__cplusplus)
// On C11 and C++, PyObject.ob_refcnt is implemented as an anonymous union
# define _PYOBJECT_REFCNT_ANON_UNION
//#elif defined(__GNUC__)
//# define _PYOBJECT_REFCNT_ANON_UNION
#endif

#ifdef Py_TRACE_REFS
/* Define pointers to support a doubly-linked list of all live heap objects. */
#define _PyObject_HEAD_EXTRA \
Expand Down Expand Up @@ -134,13 +141,21 @@ check by comparing the reference count field to the immortality reference count.
{ _Py_IMMORTAL_REFCNT }, \
(type) \
},
#else
#elif defined(_PYOBJECT_REFCNT_ANON_UNION)
#define PyObject_HEAD_INIT(type) \
{ \
_PyObject_EXTRA_INIT \
{ 1 }, \
(type) \
},
#else
// gh-105059: On C99 and older, PyObject.ob_refcnt type is Py_ssize_t
#define PyObject_HEAD_INIT(type) \
{ \
_PyObject_EXTRA_INIT \
1, \
(type) \
},
#endif /* Py_BUILD_CORE */

#define PyVarObject_HEAD_INIT(type, size) \
Expand All @@ -158,19 +173,31 @@ check by comparing the reference count field to the immortality reference count.
#define PyObject_VAR_HEAD PyVarObject ob_base;
#define Py_INVALID_SIZE (Py_ssize_t)-1


/* Nothing is actually declared to be a PyObject, but every pointer to
* a Python object can be cast to a PyObject*. This is inheritance built
* by hand. Similarly every pointer to a variable-size Python object can,
* in addition, be cast to PyVarObject*.
*/
struct _object {
_PyObject_HEAD_EXTRA
#ifdef _PYOBJECT_REFCNT_ANON_UNION

// #if defined(__GNUC__) && !(defined __STDC_VERSION__ && __STDC_VERSION__ >= 201112L)
// // On C99 and older, anonymous union is a GCC extension
// __extension__
// #endif
union {
Py_ssize_t ob_refcnt;
#if SIZEOF_VOID_P > 4
PY_UINT32_T ob_refcnt_split[2];
#endif
};
#else
// gh-105059: C99 and older cannot use anonymous union: implement
// Py_INCREF() and Py_DECREF() as opaque function calls.
Py_ssize_t ob_refcnt;
#endif
PyTypeObject *ob_type;
};

Expand Down Expand Up @@ -611,15 +638,19 @@ PyAPI_FUNC(void) _Py_DecRef(PyObject *);
static inline Py_ALWAYS_INLINE void Py_INCREF(PyObject *op)
{
#if defined(Py_LIMITED_API) && (Py_LIMITED_API+0 >= 0x030c0000 || defined(Py_REF_DEBUG))
// Stable ABI implements Py_INCREF() as a function call on limited C API
// version 3.12 and newer, and on Python built in debug mode. _Py_IncRef()
// was added to Python 3.10.0a7, use Py_IncRef() on older Python versions.
// Py_IncRef() accepts NULL whereas _Py_IncRef() doesn't.
// In limited C API version 3.12 and newer and on Python built in debug
// mode, Py_INCREF() is implemented as a function call. _Py_IncRef() was
// added to Python 3.10.0a7, use Py_IncRef() on older Python versions.
// Py_IncRef() accepts NULL, whereas _Py_IncRef() doesn't.
# if Py_LIMITED_API+0 >= 0x030a00A7
_Py_IncRef(op);
# else
Py_IncRef(op);
# endif
#elif !defined(_PYOBJECT_REFCNT_ANON_UNION)
// gh-105059: On C99 and older, Py_INCREF() is implemented as an opaque
// function call.
_Py_IncRef(op);
#else
// Non-limited C API and limited C API for Python 3.9 and older access
// directly PyObject.ob_refcnt.
Expand Down Expand Up @@ -649,10 +680,10 @@ static inline Py_ALWAYS_INLINE void Py_INCREF(PyObject *op)
#endif

#if defined(Py_LIMITED_API) && (Py_LIMITED_API+0 >= 0x030c0000 || defined(Py_REF_DEBUG))
// Stable ABI implements Py_DECREF() as a function call on limited C API
// version 3.12 and newer, and on Python built in debug mode. _Py_DecRef() was
// added to Python 3.10.0a7, use Py_DecRef() on older Python versions.
// Py_DecRef() accepts NULL whereas _Py_IncRef() doesn't.
// In limited C API version 3.12 and newer and on Python built in debug mode,
// Py_DECREF() is implemented as a function call. _Py_DecRef() was added to
// Python 3.10.0a7, use Py_DecRef() on older Python versions. Py_DecRef()
// accepts NULL, whereas _Py_DecRef() doesn't.
static inline void Py_DECREF(PyObject *op) {
# if Py_LIMITED_API+0 >= 0x030a00A7
_Py_DecRef(op);
Expand All @@ -662,6 +693,14 @@ static inline void Py_DECREF(PyObject *op) {
}
#define Py_DECREF(op) Py_DECREF(_PyObject_CAST(op))

#elif !defined(_PYOBJECT_REFCNT_ANON_UNION)
// gh-105059: On C99 and older, Py_INCREF() is implemented as an opaque
// function call.
static inline void Py_DECREF(PyObject *op) {
_Py_DecRef(op);
}
#define Py_DECREF(op) Py_DECREF(_PyObject_CAST(op))

#elif defined(Py_REF_DEBUG)
static inline void Py_DECREF(const char *filename, int lineno, PyObject *op)
{
Expand Down
38 changes: 34 additions & 4 deletions Objects/object.c
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Original file line number Diff line number Diff line change
Expand Up @@ -271,15 +271,45 @@ Py_DecRef(PyObject *o)
}

void
_Py_IncRef(PyObject *o)
_Py_IncRef(PyObject *op)
{
Py_INCREF(o);
#ifdef _PYOBJECT_REFCNT_ANON_UNION
Py_INCREF(op);
#else
// Explicitly check immortality against the immortal value
if (_Py_IsImmortal(op)) {
return;
}
op->ob_refcnt++;
#endif
_Py_INCREF_STAT_INC();
#ifdef Py_REF_DEBUG
_Py_IncRefTotal_DO_NOT_USE_THIS();
#endif
}

void
_Py_DecRef(PyObject *o)
_Py_DecRef(PyObject *op)
{
Py_DECREF(o);
#ifdef _PYOBJECT_REFCNT_ANON_UNION
Py_DECREF(op);
#else
if (_Py_IsImmortal(op)) {
return;
}
_Py_DECREF_STAT_INC();
#ifdef Py_REF_DEBUG
_Py_DecRefTotal_DO_NOT_USE_THIS();
#endif
if (--op->ob_refcnt != 0) {
if (op->ob_refcnt < 0) {
_Py_NegativeRefcount(__FILE__, __LINE__, op);
}
}
else {
_Py_Dealloc(op);
}
#endif
}


Expand Down