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bpo-43693: Add new internal code objects fields: co_fastlocalnames and co_fastlocalkinds. (gh-26388)

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A number of places in the code base (notably ceval.c and frameobject.c) rely on mapping variable names to indices in the frame "locals plus" array (AKA fast locals), and thus opargs.  Currently the compiler indirectly encodes that information on the code object as the tuples co_varnames, co_cellvars, and co_freevars.  At runtime the dependent code must calculate the proper mapping from those, which isn't ideal and impacts performance-sensitive sections.  This is something we can easily address in the compiler instead.

This change addresses the situation by replacing internal use of co_varnames, etc. with a single combined tuple of names in locals-plus order, along with a minimal array mapping each to its kind (local vs. cell vs. free).  These two new PyCodeObject fields, co_fastlocalnames and co_fastllocalkinds, are not exposed to Python code for now, but co_varnames, etc. are still available with the same values as before (though computed lazily).

Aside from the (mild) performance impact, there are a number of other benefits:

* there's now a clear, direct relationship between locals-plus and variables
* code that relies on the locals-plus-to-name mapping is simpler
* marshaled code objects are smaller and serialize/de-serialize faster

Also note that we can take this approach further by expanding the possible values in co_fastlocalkinds to include specific argument types (e.g. positional-only, kwargs).  Doing so would allow further speed-ups in _PyEval_MakeFrameVector(), which is where args get unpacked into the locals-plus array.  It would also allow us to shrink marshaled code objects even further.

https://bugs.python.org/issue43693
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Eric Snow 2021-06-03 10:28:27 -06:00 • committed by GitHub
parent ea0210fa8c
commit 2c1e2583fd
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21 changed files with 5971 additions and 5663 deletions
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225
Objects/frameobject.c
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@ -4,6 +4,7 @@
#include "pycore_ceval.h" // _PyEval_BuiltinsFromGlobals()
#include "pycore_moduleobject.h" // _PyModule_GetDict()
#include "pycore_object.h" // _PyObject_GC_UNTRACK()
#include "pycore_code.h" // CO_FAST_LOCAL, etc.
#include "frameobject.h" // PyFrameObject
#include "pycore_frame.h"
@ -659,9 +660,9 @@ frame_traverse(PyFrameObject *f, visitproc visit, void *arg)
Py_VISIT(f->f_trace);
/* locals */
PyObject **fastlocals = f->f_localsptr;
for (Py_ssize_t i = frame_nslots(f); --i >= 0; ++fastlocals) {
Py_VISIT(*fastlocals);
PyObject **localsplus = f->f_localsptr;
for (Py_ssize_t i = frame_nslots(f); --i >= 0; ++localsplus) {
Py_VISIT(*localsplus);
}
/* stack */
@ -684,9 +685,9 @@ frame_tp_clear(PyFrameObject *f)
Py_CLEAR(f->f_trace);
/* locals */
PyObject **fastlocals = f->f_localsptr;
for (Py_ssize_t i = frame_nslots(f); --i >= 0; ++fastlocals) {
Py_CLEAR(*fastlocals);
PyObject **localsplus = f->f_localsptr;
for (Py_ssize_t i = frame_nslots(f); --i >= 0; ++localsplus) {
Py_CLEAR(*localsplus);
}
/* stack */
@ -917,112 +918,13 @@ PyFrame_New(PyThreadState *tstate, PyCodeObject *code,
return f;
}
/* Convert between "fast" version of locals and dictionary version.
map and values are input arguments. map is a tuple of strings.
values is an array of PyObject*. At index i, map[i] is the name of
the variable with value values[i]. The function copies the first
nmap variable from map/values into dict. If values[i] is NULL,
the variable is deleted from dict.
If deref is true, then the values being copied are cell variables
and the value is extracted from the cell variable before being put
in dict.
*/
static int
map_to_dict(PyObject *map, Py_ssize_t nmap, PyObject *dict, PyObject **values,
int deref)
{
Py_ssize_t j;
assert(PyTuple_Check(map));
assert(PyDict_Check(dict));
assert(PyTuple_Size(map) >= nmap);
for (j=0; j < nmap; j++) {
PyObject *key = PyTuple_GET_ITEM(map, j);
PyObject *value = values[j];
assert(PyUnicode_Check(key));
if (deref && value != NULL) {
assert(PyCell_Check(value));
value = PyCell_GET(value);
}
if (value == NULL) {
if (PyObject_DelItem(dict, key) != 0) {
if (PyErr_ExceptionMatches(PyExc_KeyError))
PyErr_Clear();
else
return -1;
}
}
else {
if (PyObject_SetItem(dict, key, value) != 0)
return -1;
}
}
return 0;
}
/* Copy values from the "locals" dict into the fast locals.
dict is an input argument containing string keys representing
variables names and arbitrary PyObject* as values.
map and values are input arguments. map is a tuple of strings.
values is an array of PyObject*. At index i, map[i] is the name of
the variable with value values[i]. The function copies the first
nmap variable from map/values into dict. If values[i] is NULL,
the variable is deleted from dict.
If deref is true, then the values being copied are cell variables
and the value is extracted from the cell variable before being put
in dict. If clear is true, then variables in map but not in dict
are set to NULL in map; if clear is false, variables missing in
dict are ignored.
Exceptions raised while modifying the dict are silently ignored,
because there is no good way to report them.
*/
static void
dict_to_map(PyObject *map, Py_ssize_t nmap, PyObject *dict, PyObject **values,
int deref, int clear)
{
Py_ssize_t j;
assert(PyTuple_Check(map));
assert(PyDict_Check(dict));
assert(PyTuple_Size(map) >= nmap);
for (j=0; j < nmap; j++) {
PyObject *key = PyTuple_GET_ITEM(map, j);
PyObject *value = PyObject_GetItem(dict, key);
assert(PyUnicode_Check(key));
/* We only care about NULLs if clear is true. */
if (value == NULL) {
PyErr_Clear();
if (!clear)
continue;
}
if (deref) {
assert(PyCell_Check(values[j]));
if (PyCell_GET(values[j]) != value) {
if (PyCell_Set(values[j], value) < 0)
PyErr_Clear();
}
} else if (values[j] != value) {
Py_XINCREF(value);
Py_XSETREF(values[j], value);
}
Py_XDECREF(value);
}
}
int
PyFrame_FastToLocalsWithError(PyFrameObject *f)
{
/* Merge fast locals into f->f_locals */
PyObject *locals, *map;
PyObject *locals;
PyObject **fast;
PyCodeObject *co;
Py_ssize_t j;
if (f == NULL) {
PyErr_BadInternalCall();
@ -1035,25 +937,9 @@ PyFrame_FastToLocalsWithError(PyFrameObject *f)
return -1;
}
co = f->f_code;
map = co->co_varnames;
if (!PyTuple_Check(map)) {
PyErr_Format(PyExc_SystemError,
"co_varnames must be a tuple, not %s",
Py_TYPE(map)->tp_name);
return -1;
}
fast = f->f_localsptr;
j = PyTuple_GET_SIZE(map);
if (j > co->co_nlocals)
j = co->co_nlocals;
if (co->co_nlocals) {
if (map_to_dict(map, j, locals, fast, 0) < 0)
return -1;
}
if (co->co_ncellvars || co->co_nfreevars) {
if (map_to_dict(co->co_cellvars, co->co_ncellvars,
locals, fast + co->co_nlocals, 1))
return -1;
for (int i = 0; i < co->co_nlocalsplus; i++) {
_PyLocalsPlusKind kind = co->co_localspluskinds[i];
/* If the namespace is unoptimized, then one of the
following cases applies:
@ -1063,10 +949,42 @@ PyFrame_FastToLocalsWithError(PyFrameObject *f)
We don't want to accidentally copy free variables
into the locals dict used by the class.
*/
if (co->co_flags & CO_OPTIMIZED) {
if (map_to_dict(co->co_freevars, co->co_nfreevars, locals,
fast + co->co_nlocals + co->co_ncellvars, 1) < 0)
if (kind & CO_FAST_FREE && !(co->co_flags & CO_OPTIMIZED)) {
continue;
}
/* Some args are also cells. For now each of those variables
has two indices in the fast array, with both marked as cells
but only one marked as an arg. That one is always set
to NULL in _PyEval_MakeFrameVector() and the other index
gets the cell holding the arg value. So we ignore the
former here and will later use the cell for the variable.
*/
if (kind & CO_FAST_LOCAL && kind & CO_FAST_CELL) {
assert(fast[i] == NULL);
continue;
}
PyObject *name = PyTuple_GET_ITEM(co->co_localsplusnames, i);
PyObject *value = fast[i];
if (kind & (CO_FAST_CELL | CO_FAST_FREE) && value != NULL) {
assert(PyCell_Check(value));
value = PyCell_GET(value);
}
if (value == NULL) {
if (PyObject_DelItem(locals, name) != 0) {
if (PyErr_ExceptionMatches(PyExc_KeyError)) {
PyErr_Clear();
}
else {
return -1;
}
}
}
else {
if (PyObject_SetItem(locals, name, value) != 0) {
return -1;
}
}
}
return 0;
@ -1088,36 +1006,51 @@ void
PyFrame_LocalsToFast(PyFrameObject *f, int clear)
{
/* Merge locals into fast locals */
PyObject *locals, *map;
PyObject *locals;
PyObject **fast;
PyObject *error_type, *error_value, *error_traceback;
PyCodeObject *co;
Py_ssize_t j;
if (f == NULL)
return;
locals = _PyFrame_Specials(f)[FRAME_SPECIALS_LOCALS_OFFSET];
co = f->f_code;
map = co->co_varnames;
if (locals == NULL)
return;
if (!PyTuple_Check(map))
return;
PyErr_Fetch(&error_type, &error_value, &error_traceback);
fast = f->f_localsptr;
j = PyTuple_GET_SIZE(map);
if (j > co->co_nlocals)
j = co->co_nlocals;
if (co->co_nlocals)
dict_to_map(co->co_varnames, j, locals, fast, 0, clear);
if (co->co_ncellvars || co->co_nfreevars) {
dict_to_map(co->co_cellvars, co->co_ncellvars,
locals, fast + co->co_nlocals, 1, clear);
co = f->f_code;
PyErr_Fetch(&error_type, &error_value, &error_traceback);
for (int i = 0; i < co->co_nlocalsplus; i++) {
_PyLocalsPlusKind kind = co->co_localspluskinds[i];
/* Same test as in PyFrame_FastToLocals() above. */
if (co->co_flags & CO_OPTIMIZED) {
dict_to_map(co->co_freevars, co->co_nfreevars, locals,
fast + co->co_nlocals + co->co_ncellvars, 1,
clear);
if (kind & CO_FAST_FREE && !(co->co_flags & CO_OPTIMIZED)) {
continue;
}
/* Same test as in PyFrame_FastToLocals() above. */
if (kind & CO_FAST_LOCAL && kind & CO_FAST_CELL) {
continue;
}
PyObject *name = PyTuple_GET_ITEM(co->co_localsplusnames, i);
PyObject *value = PyObject_GetItem(locals, name);
/* We only care about NULLs if clear is true. */
if (value == NULL) {
PyErr_Clear();
if (!clear) {
continue;
}
}
if (kind & (CO_FAST_CELL | CO_FAST_FREE)) {
assert(PyCell_Check(fast[i]));
if (PyCell_GET(fast[i]) != value) {
if (PyCell_Set(fast[i], value) < 0) {
PyErr_Clear();
}
}
} else if (fast[i] != value) {
Py_XINCREF(value);
Py_XSETREF(fast[i], value);
}
Py_XDECREF(value);
}
PyErr_Restore(error_type, error_value, error_traceback);
}