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bpo-43693: Eliminate unused "fast locals". (gh-26587)

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Currently, if an arg value escapes (into the closure for an inner function) we end up allocating two indices in the fast locals even though only one gets used.  Additionally, using the lower index would be better in some cases, such as with no-arg `super()`.  To address this, we update the compiler to fix the offsets so each variable only gets one "fast local".  As a consequence, now some cell offsets are interspersed with the locals (only when an arg escapes to an inner function).

https://bugs.python.org/issue43693
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Eric Snow 2021-06-15 16:35:25 -06:00 • committed by GitHub
parent 1d10bf0bb9
commit ac38a9f2df
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GPG key ID: 4AEE18F83AFDEB23
12 changed files with 4189 additions and 4214 deletions
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32
Objects/typeobject.c
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@ -11,7 +11,6 @@
#include "pycore_pystate.h" // _PyThreadState_GET()
#include "pycore_unionobject.h" // _Py_Union(), _Py_union_type_or
#include "frameobject.h"
#include "pycore_frame.h" // _PyFrame_OpAlreadyRan
#include "opcode.h" // MAKE_CELL
#include "structmember.h" // PyMemberDef
@ -8878,23 +8877,18 @@ super_init_without_args(PyFrameObject *f, PyCodeObject *co,
return -1;
}
PyObject *obj = f->f_localsptr[0];
int i;
if (obj == NULL && co->co_cell2arg) {
/* The first argument might be a cell. */
for (i = 0; i < co->co_ncellvars; i++) {
if (co->co_cell2arg[i] == 0) {
int celloffset = co->co_nlocals + i;
PyObject *cell = f->f_localsptr[celloffset];
if (PyCell_Check(cell) &&
_PyFrame_OpAlreadyRan(f, MAKE_CELL, celloffset)) {
obj = PyCell_GET(cell);
}
break;
}
PyObject *firstarg = f->f_localsptr[0];
// The first argument might be a cell.
if (firstarg != NULL && (co->co_localspluskinds[0] & CO_FAST_CELL)) {
// "firstarg" is a cell here unless (very unlikely) super()
// was called from the C-API before the first MAKE_CELL op.
if (f->f_lasti >= 0) {
assert(_Py_OPCODE(*co->co_firstinstr) == MAKE_CELL);
assert(PyCell_Check(firstarg));
firstarg = PyCell_GET(firstarg);
}
}
if (obj == NULL) {
if (firstarg == NULL) {
PyErr_SetString(PyExc_RuntimeError,
"super(): arg[0] deleted");
return -1;
@ -8902,9 +8896,9 @@ super_init_without_args(PyFrameObject *f, PyCodeObject *co,
// Look for __class__ in the free vars.
PyTypeObject *type = NULL;
i = co->co_nlocals + co->co_ncellvars;
int i = co->co_nlocals + co->co_nplaincellvars;
for (; i < co->co_nlocalsplus; i++) {
assert(co->co_localspluskinds[i] & CO_FAST_FREE);
assert((co->co_localspluskinds[i] & CO_FAST_FREE) != 0);
PyObject *name = PyTuple_GET_ITEM(co->co_localsplusnames, i);
assert(PyUnicode_Check(name));
if (_PyUnicode_EqualToASCIIId(name, &PyId___class__)) {
@ -8936,7 +8930,7 @@ super_init_without_args(PyFrameObject *f, PyCodeObject *co,
}
*type_p = type;
*obj_p = obj;
*obj_p = firstarg;
return 0;
}