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gh-117139: Convert the evaluation stack to stack refs (#118450)

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This PR sets up tagged pointers for CPython.

The general idea is to create a separate struct _PyStackRef for everything on the evaluation stack to store the bits. This forces the C compiler to warn us if we try to cast things or pull things out of the struct directly.

Only for free threading: We tag the low bit if something is deferred - that means we skip incref and decref operations on it. This behavior may change in the future if Mark's plans to defer all objects in the interpreter loop pans out.

This implies a strict stack reference discipline is required. ALL incref and decref operations on stackrefs must use the stackref variants. It is unsafe to untag something then do normal incref/decref ops on it.

The new incref and decref variants are called dup and close. They mimic a "handle" API operating on these stackrefs.

Please read Include/internal/pycore_stackref.h for more information!

---------

Co-authored-by: Mark Shannon <9448417+markshannon@users.noreply.github.com>
This commit is contained in:
Ken Jin 2024-06-27 03:10:43 +08:00 • committed by GitHub
parent d611c4c8e9
commit 22b0de2755
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35 changed files with 5228 additions and 3758 deletions
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35
Python/ceval_macros.h
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@ -264,9 +264,9 @@ GETITEM(PyObject *v, Py_ssize_t i) {
This is because it is possible that during the DECREF the frame is
accessed by other code (e.g. a __del__ method or gc.collect()) and the
variable would be pointing to already-freed memory. */
#define SETLOCAL(i, value) do { PyObject *tmp = GETLOCAL(i); \
#define SETLOCAL(i, value) do { _PyStackRef tmp = GETLOCAL(i); \
GETLOCAL(i) = value; \
Py_XDECREF(tmp); } while (0)
PyStackRef_XCLOSE(tmp); } while (0)
#define GO_TO_INSTRUCTION(op) goto PREDICT_ID(op)
@ -449,3 +449,34 @@ do { \
#define EXIT_TO_TRACE() goto exit_to_trace
#define EXIT_TO_TIER1() goto exit_to_tier1
#define EXIT_TO_TIER1_DYNAMIC() goto exit_to_tier1_dynamic;
/* Stackref macros */
/* How much scratch space to give stackref to PyObject* conversion. */
#define MAX_STACKREF_SCRATCH 10
#ifdef Py_GIL_DISABLED
#define STACKREFS_TO_PYOBJECTS(ARGS, ARG_COUNT, NAME) \
/* +1 because vectorcall might use -1 to write self */ \
PyObject *NAME##_temp[MAX_STACKREF_SCRATCH+1]; \
PyObject **NAME = _PyObjectArray_FromStackRefArray(ARGS, ARG_COUNT, NAME##_temp + 1);
#else
#define STACKREFS_TO_PYOBJECTS(ARGS, ARG_COUNT, NAME) \
PyObject **NAME = (PyObject **)ARGS; \
assert(NAME != NULL);
#endif
#ifdef Py_GIL_DISABLED
#define STACKREFS_TO_PYOBJECTS_CLEANUP(NAME) \
/* +1 because we +1 previously */ \
_PyObjectArray_Free(NAME - 1, NAME##_temp);
#else
#define STACKREFS_TO_PYOBJECTS_CLEANUP(NAME) \
(void)(NAME);
#endif
#ifdef Py_GIL_DISABLED
#define CONVERSION_FAILED(NAME) ((NAME) == NULL)
#else
#define CONVERSION_FAILED(NAME) (0)
#endif