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gh-98831: Modernize the FOR_ITER family of instructions #101626

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Merged
merged 7 commits into from
Feb 7, 2023
Merged

gh-98831: Modernize the FOR_ITER family of instructions #101626

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5869fba
Modernize FOR_ITER
gvanrossum Feb 6, 2023
bd65e1c
Modernize FOR_ITER_LIST
gvanrossum Feb 6, 2023
872e156
Modernize FOR_ITER_TUPLE
gvanrossum Feb 6, 2023
a52a79d
Modernize FOR_ITER_RANGE (even weirder)
gvanrossum Feb 7, 2023
53cfd22
Modernize FOR_ITER_GEN
gvanrossum Feb 7, 2023
76a4a7b
Accept comment suggestion
gvanrossum Feb 7, 2023
b39cf90
Update generated file
gvanrossum Feb 7, 2023
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83 changes: 47 additions & 36 deletions Python/bytecodes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2066,27 +2066,35 @@ dummy_func(
PREDICT(LOAD_CONST);
}

// stack effect: ( -- __0)
inst(FOR_ITER) {
// Most members of this family are "secretly" super-instructions.
// When the loop is exhausted, they jump, and the jump target is
// always END_FOR, which pops two values off the stack.
// This is optimized by skipping that instruction and combining
// its effect (popping 'iter' instead of pushing 'next'.)

family(for_iter, INLINE_CACHE_ENTRIES_FOR_ITER) = {
FOR_ITER,
FOR_ITER_LIST,
FOR_ITER_TUPLE,
FOR_ITER_RANGE,
FOR_ITER_GEN,
};

inst(FOR_ITER, (unused/1, iter -- iter, next)) {
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Should this be counter/1 instead of unused/1, and then the counter used in the body?

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In all cases where the counter is manipulated using ADAPTIVE_COUNTER_IS_ZERO / DECREMENT_ADAPTIVE_COUNTER I'm leaving this idiom unchanged -- the generator won't let you write back to cache entries, so it would become asymmetrical, and the common case is DECREMENT_ADAPTIVE_COUNTER anyway.

#if ENABLE_SPECIALIZATION
_PyForIterCache *cache = (_PyForIterCache *)next_instr;
if (ADAPTIVE_COUNTER_IS_ZERO(cache->counter)) {
assert(cframe.use_tracing == 0);
next_instr--;
_Py_Specialize_ForIter(TOP(), next_instr, oparg);
_Py_Specialize_ForIter(iter, next_instr, oparg);
DISPATCH_SAME_OPARG();
}
STAT_INC(FOR_ITER, deferred);
DECREMENT_ADAPTIVE_COUNTER(cache->counter);
#endif /* ENABLE_SPECIALIZATION */
/* before: [iter]; after: [iter, iter()] *or* [] */
PyObject *iter = TOP();
PyObject *next = (*Py_TYPE(iter)->tp_iternext)(iter);
if (next != NULL) {
PUSH(next);
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER);
}
else {
/* before: [iter]; after: [iter, iter()] *or* [] (and jump over END_FOR.) */
next = (*Py_TYPE(iter)->tp_iternext)(iter);
if (next == NULL) {
if (_PyErr_Occurred(tstate)) {
if (!_PyErr_ExceptionMatches(tstate, PyExc_StopIteration)) {
goto error;
Expand All @@ -2098,70 +2106,74 @@ dummy_func(
}
/* iterator ended normally */
assert(_Py_OPCODE(next_instr[INLINE_CACHE_ENTRIES_FOR_ITER + oparg]) == END_FOR);
STACK_SHRINK(1);
Py_DECREF(iter);
/* Skip END_FOR */
STACK_SHRINK(1);
/* Jump forward oparg, then skip following END_FOR instruction */
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + oparg + 1);
DISPATCH();
}
// Common case: no jump, leave it to the code generator
}

// stack effect: ( -- __0)
inst(FOR_ITER_LIST) {
inst(FOR_ITER_LIST, (unused/1, iter -- iter, next)) {
assert(cframe.use_tracing == 0);
_PyListIterObject *it = (_PyListIterObject *)TOP();
DEOPT_IF(Py_TYPE(it) != &PyListIter_Type, FOR_ITER);
DEOPT_IF(Py_TYPE(iter) != &PyListIter_Type, FOR_ITER);
_PyListIterObject *it = (_PyListIterObject *)iter;
STAT_INC(FOR_ITER, hit);
PyListObject *seq = it->it_seq;
if (seq) {
if (it->it_index < PyList_GET_SIZE(seq)) {
PyObject *next = PyList_GET_ITEM(seq, it->it_index++);
PUSH(Py_NewRef(next));
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER);
next = Py_NewRef(PyList_GET_ITEM(seq, it->it_index++));
goto end_for_iter_list; // End of this instruction
}
it->it_seq = NULL;
Py_DECREF(seq);
}
Py_DECREF(iter);
STACK_SHRINK(1);
Py_DECREF(it);
/* Jump forward oparg, then skip following END_FOR instruction */
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + oparg + 1);
DISPATCH();
end_for_iter_list:
// Common case: no jump, leave it to the code generator
}

// stack effect: ( -- __0)
inst(FOR_ITER_TUPLE) {
inst(FOR_ITER_TUPLE, (unused/1, iter -- iter, next)) {
assert(cframe.use_tracing == 0);
_PyTupleIterObject *it = (_PyTupleIterObject *)TOP();
_PyTupleIterObject *it = (_PyTupleIterObject *)iter;
DEOPT_IF(Py_TYPE(it) != &PyTupleIter_Type, FOR_ITER);
STAT_INC(FOR_ITER, hit);
PyTupleObject *seq = it->it_seq;
if (seq) {
if (it->it_index < PyTuple_GET_SIZE(seq)) {
PyObject *next = PyTuple_GET_ITEM(seq, it->it_index++);
PUSH(Py_NewRef(next));
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER);
next = Py_NewRef(PyTuple_GET_ITEM(seq, it->it_index++));
goto end_for_iter_tuple; // End of this instruction
}
it->it_seq = NULL;
Py_DECREF(seq);
}
Py_DECREF(iter);
STACK_SHRINK(1);
Py_DECREF(it);
/* Jump forward oparg, then skip following END_FOR instruction */
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + oparg + 1);
DISPATCH();
end_for_iter_tuple:
// Common case: no jump, leave it to the code generator
}

// stack effect: ( -- __0)
inst(FOR_ITER_RANGE) {
// This is slightly different, when the loop isn't terminated we
// jump over the immediately following STORE_FAST instruction.
inst(FOR_ITER_RANGE, (unused/1, iter -- iter, unused)) {
assert(cframe.use_tracing == 0);
_PyRangeIterObject *r = (_PyRangeIterObject *)TOP();
_PyRangeIterObject *r = (_PyRangeIterObject *)iter;
DEOPT_IF(Py_TYPE(r) != &PyRangeIter_Type, FOR_ITER);
STAT_INC(FOR_ITER, hit);
_Py_CODEUNIT next = next_instr[INLINE_CACHE_ENTRIES_FOR_ITER];
assert(_PyOpcode_Deopt[_Py_OPCODE(next)] == STORE_FAST);
if (r->len <= 0) {
STACK_SHRINK(1);
Py_DECREF(r);
// Jump over END_FOR instruction.
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + oparg + 1);
}
else {
Expand All @@ -2174,11 +2186,13 @@ dummy_func(
// The STORE_FAST is already done.
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + 1);
}
DISPATCH();
}

inst(FOR_ITER_GEN) {
// This is *not* a super-instruction, unique in the family.
inst(FOR_ITER_GEN, (unused/1, iter -- iter, unused)) {
assert(cframe.use_tracing == 0);
PyGenObject *gen = (PyGenObject *)TOP();
PyGenObject *gen = (PyGenObject *)iter;
DEOPT_IF(Py_TYPE(gen) != &PyGen_Type, FOR_ITER);
DEOPT_IF(gen->gi_frame_state >= FRAME_EXECUTING, FOR_ITER);
STAT_INC(FOR_ITER, hit);
Expand Down Expand Up @@ -3173,9 +3187,6 @@ family(call, INLINE_CACHE_ENTRIES_CALL) = {
CALL_NO_KW_LIST_APPEND, CALL_NO_KW_METHOD_DESCRIPTOR_FAST, CALL_NO_KW_METHOD_DESCRIPTOR_NOARGS,
CALL_NO_KW_METHOD_DESCRIPTOR_O, CALL_NO_KW_STR_1, CALL_NO_KW_TUPLE_1,
CALL_NO_KW_TYPE_1 };
family(for_iter, INLINE_CACHE_ENTRIES_FOR_ITER) = {
FOR_ITER, FOR_ITER_LIST,
FOR_ITER_RANGE };
family(store_fast) = { STORE_FAST, STORE_FAST__LOAD_FAST, STORE_FAST__STORE_FAST };
family(unpack_sequence, INLINE_CACHE_ENTRIES_UNPACK_SEQUENCE) = {
UNPACK_SEQUENCE, UNPACK_SEQUENCE_LIST,
Expand Down
66 changes: 42 additions & 24 deletions Python/generated_cases.c.h
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30 changes: 15 additions & 15 deletions Python/opcode_metadata.h
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Original file line number Diff line number Diff line change
Expand Up @@ -261,15 +261,15 @@ _PyOpcode_num_popped(int opcode, int oparg, bool jump) {
case GET_YIELD_FROM_ITER:
return 1;
case FOR_ITER:
return -1;
return 1;
case FOR_ITER_LIST:
return -1;
return 1;
case FOR_ITER_TUPLE:
return -1;
return 1;
case FOR_ITER_RANGE:
return -1;
return 1;
case FOR_ITER_GEN:
return -1;
return 1;
case BEFORE_ASYNC_WITH:
return 1;
case BEFORE_WITH:
Expand Down Expand Up @@ -607,15 +607,15 @@ _PyOpcode_num_pushed(int opcode, int oparg, bool jump) {
case GET_YIELD_FROM_ITER:
return 1;
case FOR_ITER:
return -1;
return 2;
case FOR_ITER_LIST:
return -1;
return 2;
case FOR_ITER_TUPLE:
return -1;
return 2;
case FOR_ITER_RANGE:
return -1;
return 2;
case FOR_ITER_GEN:
return -1;
return 2;
case BEFORE_ASYNC_WITH:
return 2;
case BEFORE_WITH:
Expand Down Expand Up @@ -829,11 +829,11 @@ struct opcode_metadata {
[MATCH_KEYS] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
[GET_ITER] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
[GET_YIELD_FROM_ITER] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
[FOR_ITER] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
[FOR_ITER_LIST] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
[FOR_ITER_TUPLE] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
[FOR_ITER_RANGE] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
[FOR_ITER_GEN] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
[FOR_ITER] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IBC },
[FOR_ITER_LIST] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IBC },
[FOR_ITER_TUPLE] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IBC },
[FOR_ITER_RANGE] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IBC },
[FOR_ITER_GEN] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IBC },
[BEFORE_ASYNC_WITH] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
[BEFORE_WITH] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
[WITH_EXCEPT_START] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
Expand Down