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GH-93143: Don't turn LOAD_FAST into LOAD_FAST_CHECK #99075

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Merged
brandtbucher merged 6 commits into from
Nov 8, 2022
Merged

GH-93143: Don't turn LOAD_FAST into LOAD_FAST_CHECK #99075

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e0f2459
Just assign None instead of changing co_code
brandtbucher Oct 20, 2022
6f68d32
blurb add
brandtbucher Oct 20, 2022
dd52da5
Feedback from code review
brandtbucher Oct 20, 2022
da07230
fixup
brandtbucher Oct 20, 2022
555d23e
Perform assignments *before* adjusting the stack
brandtbucher Oct 20, 2022
4e597b3
Address code review
brandtbucher Oct 21, 2022
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Feedback from code review
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@brandtbucher
brandtbucher committed Oct 20, 2022
commit dd52da542cc149a005a37ddde1030e08f1541227
78 changes: 72 additions & 6 deletions Lib/test/test_peepholer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -815,10 +815,42 @@ def f():
self.assertInBytecode(f, 'LOAD_FAST_CHECK', "a73")
self.assertInBytecode(f, 'LOAD_FAST', "a73")

def test_setting_lineno_adds_check(self):
code = textwrap.dedent("""\
def test_setting_lineno_warns_and_assigns_none_0(self):
code = textwrap.dedent(f"""\
def f():
x = 2
x = y = 2
if not x:
return 4
for i in range(55):
x + 6
L = 7
L = 8
L = 9
L = 10
""")
ns = {}
exec(code, ns)
f = ns['f']
self.assertInBytecode(f, "LOAD_FAST")
self.assertNotInBytecode(f, "LOAD_FAST_CHECK")
co_code = f.__code__.co_code
def trace(frame, event, arg):
if event == 'line' and frame.f_lineno == 9:
frame.f_lineno = 3
sys.settrace(None)
return None
return trace
sys.settrace(trace)
result = f()
self.assertIsNone(result)
self.assertInBytecode(f, "LOAD_FAST")
self.assertNotInBytecode(f, "LOAD_FAST_CHECK")
self.assertEqual(f.__code__.co_code, co_code)

def test_setting_lineno_warns_and_assigns_none_1(self):
code = textwrap.dedent(f"""\
def f():
x = y = 2
if not x:
return 4
for i in range(55):
Expand All @@ -840,7 +872,41 @@ def trace(frame, event, arg):
sys.settrace(None)
return None
return trace
e = r"cannot leave local name 'x' unbound \(assigning None\)"
e = r"assigning None to 1 unbound local"
with self.assertWarnsRegex(RuntimeWarning, e):
sys.settrace(trace)
result = f()
self.assertEqual(result, 4)
self.assertInBytecode(f, "LOAD_FAST")
self.assertNotInBytecode(f, "LOAD_FAST_CHECK")
self.assertEqual(f.__code__.co_code, co_code)

def test_setting_lineno_warns_and_assigns_none_2(self):
code = textwrap.dedent(f"""\
def f():
x = y = 2
if not x:
return 4
for i in range(55):
x + 6
del x, y
L = 8
L = 9
L = 10
""")
ns = {}
exec(code, ns)
f = ns['f']
self.assertInBytecode(f, "LOAD_FAST")
self.assertNotInBytecode(f, "LOAD_FAST_CHECK")
co_code = f.__code__.co_code
def trace(frame, event, arg):
if event == 'line' and frame.f_lineno == 9:
frame.f_lineno = 3
sys.settrace(None)
return None
return trace
e = r"assigning None to 2 unbound locals"
with self.assertWarnsRegex(RuntimeWarning, e):
sys.settrace(trace)
result = f()
Expand All @@ -867,7 +933,7 @@ def f():
self.assertNotInBytecode(f, "LOAD_FAST_CHECK")
return f

def test_deleting_local_adds_check(self):
def test_deleting_local_warns_and_assigns_none(self):
f = self.make_function_with_no_checks()
co_code = f.__code__.co_code
def trace(frame, event, arg):
Expand All @@ -876,7 +942,7 @@ def trace(frame, event, arg):
sys.settrace(None)
return None
return trace
e = r"cannot leave local name 'x' unbound \(assigning None\)"
e = r"assigning None to unbound local 'x'"
with self.assertWarnsRegex(RuntimeWarning, e):
sys.settrace(trace)
f()
Expand Down
113 changes: 61 additions & 52 deletions Objects/frameobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -620,49 +620,6 @@ _PyFrame_GetState(PyFrameObject *frame)
Py_UNREACHABLE();
}

static bool
op_exists(PyCodeObject *co, int opcode, int oparg, int start, int stop)
{
// This only works when opcode is a non-quickened form:
assert(_PyOpcode_Deopt[opcode] == opcode);
int check_oparg = 0;
_Py_CODEUNIT *instructions = _PyCode_CODE(co);
while (start < stop) {
int check_opcode = _PyOpcode_Deopt[_Py_OPCODE(instructions[start])];
check_oparg |= _Py_OPARG(instructions[start]);
if (check_opcode == opcode && check_oparg == oparg) {
return true;
}
if (check_opcode == EXTENDED_ARG) {
check_oparg <<= 8;
}
else {
check_oparg = 0;
}
start += 1 + _PyOpcode_Caches[check_opcode];
}
return false;
}

static void
maybe_bind_fast_local(_PyInterpreterFrame *f, int i)
{
PyCodeObject *co = f->f_code;
if (f->localsplus[i] == NULL && op_exists(co, LOAD_FAST, i, 0, Py_SIZE(co)))
{
// We're being overly-cautious here (it's too expensive to run a full
// flow analysis), but at least one instruction expects i to be bound.
// Rather than crashing (or changing co_code), just bind None instead:
const char *e = "cannot leave local name %R unbound (assigning None)";
PyObject *name = PyTuple_GET_ITEM(co->co_localsplusnames, i);
if (PyErr_WarnFormat(PyExc_RuntimeWarning, 0, e, name)) {
// It's okay if frame_obj is NULL, just try anyways:
PyErr_WriteUnraisable((PyObject *)f->frame_obj);
}
f->localsplus[i] = Py_NewRef(Py_None);
}
}

Comment thread
brandtbucher marked this conversation as resolved.
/* Setter for f_lineno - you can set f_lineno from within a trace function in
* order to jump to a given line of code, subject to some restrictions. Most
* lines are OK to jump to because they don't make any assumptions about the
Expand Down Expand Up @@ -831,9 +788,30 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno, void *Py_UNUSED(ignore
}
start_stack = pop_value(start_stack);
}
// Populate any NULL locals that might be needed:
// Populate any NULL locals that the compiler might have "proven" to exist
// in the new location. Rather than crashing or changing co_code, just bind
// None instead:
int empty = 0;
for (int i = 0; i < f->f_frame->f_code->co_nlocalsplus; i++) {
maybe_bind_fast_local(f->f_frame, i);
// Counting every unbound local is overly-cautious, but a full flow
// analysis (like we do in the compiler) is probably too expensive:
empty += f->f_frame->localsplus[i] == NULL;
}
if (empty) {
const char *e = "assigning None to %d unbound local%s";
const char *s = (empty == 1) ? "" : "s";
if (PyErr_WarnFormat(PyExc_RuntimeWarning, 0, e, empty, s)) {
return -1;
}
// Do this in a second pass to avoid writing a bunch of Nones when
// warnings are being treated as errors and the previous bit raises:
for (int i = 0; i < f->f_frame->f_code->co_nlocalsplus; i++) {
if (f->f_frame->localsplus[i] == NULL) {
f->f_frame->localsplus[i] = Py_NewRef(Py_None);
empty--;
}
}
assert(empty == 0);
}
/* Finally set the new lasti and return OK. */
f->f_lineno = 0;
Expand Down Expand Up @@ -1117,6 +1095,31 @@ PyFrame_New(PyThreadState *tstate, PyCodeObject *code,
return f;
}

static int
_PyFrame_OpAlreadyRan(_PyInterpreterFrame *frame, int opcode, int oparg)
{
// This only works when opcode is a non-quickened form:
assert(_PyOpcode_Deopt[opcode] == opcode);
int check_oparg = 0;
for (_Py_CODEUNIT *instruction = _PyCode_CODE(frame->f_code);
instruction < frame->prev_instr; instruction++)
{
int check_opcode = _PyOpcode_Deopt[_Py_OPCODE(*instruction)];
check_oparg |= _Py_OPARG(*instruction);
if (check_opcode == opcode && check_oparg == oparg) {
return 1;
}
if (check_opcode == EXTENDED_ARG) {
check_oparg <<= 8;
}
else {
check_oparg = 0;
}
instruction += _PyOpcode_Caches[check_opcode];
}
return 0;
}

int
_PyFrame_FastToLocalsWithError(_PyInterpreterFrame *frame) {
/* Merge fast locals into f->f_locals */
Expand Down Expand Up @@ -1179,8 +1182,7 @@ _PyFrame_FastToLocalsWithError(_PyInterpreterFrame *frame) {
// run yet.
if (value != NULL) {
if (PyCell_Check(value) &&
op_exists(co, MAKE_CELL, i, 0, lasti))
{
_PyFrame_OpAlreadyRan(frame, MAKE_CELL, i)) {
// (likely) MAKE_CELL must have executed already.
value = PyCell_GET(value);
}
Expand Down Expand Up @@ -1254,7 +1256,6 @@ _PyFrame_LocalsToFast(_PyInterpreterFrame *frame, int clear)
}
fast = _PyFrame_GetLocalsArray(frame);
co = frame->f_code;
int lasti = _PyInterpreterFrame_LASTI(frame);

PyErr_Fetch(&error_type, &error_value, &error_traceback);
for (int i = 0; i < co->co_nlocalsplus; i++) {
Expand Down Expand Up @@ -1283,8 +1284,8 @@ _PyFrame_LocalsToFast(_PyInterpreterFrame *frame, int clear)
}
else if (kind & CO_FAST_CELL && oldvalue != NULL) {
/* Same test as in PyFrame_FastToLocals() above. */
if (PyCell_Check(oldvalue) && op_exists(co, MAKE_CELL, i, 0, lasti))
{
if (PyCell_Check(oldvalue) &&
_PyFrame_OpAlreadyRan(frame, MAKE_CELL, i)) {
// (likely) MAKE_CELL must have executed already.
cell = oldvalue;
}
Expand All @@ -1300,10 +1301,18 @@ _PyFrame_LocalsToFast(_PyInterpreterFrame *frame, int clear)
}
}
else if (value != oldvalue) {
if (value == NULL) {
// Probably can't delete this, since the compiler's flow
// analysis may have already "proved" that it exists here:
const char *e = "assigning None to unbound local %R";
if (PyErr_WarnFormat(PyExc_RuntimeWarning, 0, e, name)) {
// It's okay if frame_obj is NULL, just try anyways:
PyErr_WriteUnraisable((PyObject *)frame->frame_obj);
}
value = Py_NewRef(Py_None);
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}
Py_XINCREF(value);

@markshannon markshannon Nov 7, 2022

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Suggested change
Py_XINCREF(value);
Py_INCREF(value);

Py_XSETREF(fast[i], value);
// Populate any NULL locals that might be needed:
maybe_bind_fast_local(frame, i);
}
Py_XDECREF(value);
}
Expand Down