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pythongh-106529: Make FOR_ITER a viable uop (python#112134)
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This uses the new mechanism whereby certain uops
are replaced by others during translation,
using the `_PyUop_Replacements` table.
We further special-case the `_FOR_ITER_TIER_TWO` uop
to update the deoptimization target to point
just past the corresponding `END_FOR` opcode.

Two tiny code cleanups are also part of this PR.
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gvanrossum authored and aisk committed Feb 11, 2024
1 parent cd41ab6 commit 1a18d22
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Showing 8 changed files with 138 additions and 43 deletions.
86 changes: 47 additions & 39 deletions Include/internal/pycore_opcode_metadata.h

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30 changes: 30 additions & 0 deletions Lib/test/test_capi/test_misc.py
Original file line number Diff line number Diff line change
Expand Up @@ -2808,6 +2808,36 @@ def testfunc(n):
uops = {opname for opname, _, _ in ex}
self.assertIn("_GUARD_IS_FALSE_POP", uops)

def test_for_iter_tier_two(self):
class MyIter:
def __init__(self, n):
self.n = n
def __iter__(self):
return self
def __next__(self):
self.n -= 1
if self.n < 0:
raise StopIteration
return self.n

def testfunc(n, m):
x = 0
for i in range(m):
for j in MyIter(n):
x += 1000*i + j
return x

opt = _testinternalcapi.get_uop_optimizer()
with temporary_optimizer(opt):
x = testfunc(10, 10)

self.assertEqual(x, sum(range(10)) * 10010)

ex = get_first_executor(testfunc)
self.assertIsNotNone(ex)
uops = {opname for opname, _, _ in ex}
self.assertIn("_FOR_ITER_TIER_TWO", uops)


if __name__ == "__main__":
unittest.main()
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Enable translating unspecialized ``FOR_ITER`` to Tier 2.
6 changes: 6 additions & 0 deletions Python/abstract_interp_cases.c.h

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23 changes: 21 additions & 2 deletions Python/bytecodes.c
Original file line number Diff line number Diff line change
Expand Up @@ -2369,7 +2369,7 @@ dummy_func(
goto enter_tier_one;
}

replaced op(_POP_JUMP_IF_FALSE, (unused/1, cond -- )) {
replaced op(_POP_JUMP_IF_FALSE, (unused/1, cond -- )) {
assert(PyBool_Check(cond));
int flag = Py_IsFalse(cond);
#if ENABLE_SPECIALIZATION
Expand Down Expand Up @@ -2513,7 +2513,7 @@ dummy_func(
#endif /* ENABLE_SPECIALIZATION */
}

op(_FOR_ITER, (iter -- iter, next)) {
replaced op(_FOR_ITER, (iter -- iter, next)) {
/* before: [iter]; after: [iter, iter()] *or* [] (and jump over END_FOR.) */
next = (*Py_TYPE(iter)->tp_iternext)(iter);
if (next == NULL) {
Expand All @@ -2536,6 +2536,25 @@ dummy_func(
// Common case: no jump, leave it to the code generator
}

op(_FOR_ITER_TIER_TWO, (iter -- iter, next)) {
/* 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(error);
}
_PyErr_Clear(tstate);
}
/* iterator ended normally */
Py_DECREF(iter);
STACK_SHRINK(1);
/* The translator sets the deopt target just past END_FOR */
DEOPT_IF(true);
}
// Common case: no jump, leave it to the code generator
}

macro(FOR_ITER) = _SPECIALIZE_FOR_ITER + _FOR_ITER;

inst(INSTRUMENTED_FOR_ITER, (unused/1 -- )) {
Expand Down
4 changes: 2 additions & 2 deletions Python/ceval.c
Original file line number Diff line number Diff line change
Expand Up @@ -1074,7 +1074,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
UOP_STAT_INC(opcode, miss);
frame->return_offset = 0; // Dispatch to frame->instr_ptr
_PyFrame_SetStackPointer(frame, stack_pointer);
frame->instr_ptr = next_uop[-1].target + _PyCode_CODE((PyCodeObject *)frame->f_executable);
frame->instr_ptr = next_uop[-1].target + _PyCode_CODE(_PyFrame_GetCode(frame));
Py_DECREF(current_executor);
// Fall through
// Jump here from ENTER_EXECUTOR
Expand All @@ -1085,7 +1085,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
// Jump here from _EXIT_TRACE
exit_trace:
_PyFrame_SetStackPointer(frame, stack_pointer);
frame->instr_ptr = next_uop[-1].target + _PyCode_CODE((PyCodeObject *)frame->f_executable);
frame->instr_ptr = next_uop[-1].target + _PyCode_CODE(_PyFrame_GetCode(frame));
Py_DECREF(current_executor);
OPT_HIST(trace_uop_execution_counter, trace_run_length_hist);
goto enter_tier_one;
Expand Down
25 changes: 25 additions & 0 deletions Python/executor_cases.c.h

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6 changes: 6 additions & 0 deletions Python/optimizer.c
Original file line number Diff line number Diff line change
Expand Up @@ -392,6 +392,7 @@ _PyUop_Replacements[OPCODE_METADATA_SIZE] = {
[_ITER_JUMP_RANGE] = _GUARD_NOT_EXHAUSTED_RANGE,
[_ITER_JUMP_LIST] = _GUARD_NOT_EXHAUSTED_LIST,
[_ITER_JUMP_TUPLE] = _GUARD_NOT_EXHAUSTED_TUPLE,
[_FOR_ITER] = _FOR_ITER_TIER_TWO,
};

static const uint16_t
Expand Down Expand Up @@ -620,6 +621,11 @@ translate_bytecode_to_trace(
}
if (_PyUop_Replacements[uop]) {
uop = _PyUop_Replacements[uop];
if (uop == _FOR_ITER_TIER_TWO) {
target += 1 + INLINE_CACHE_ENTRIES_FOR_ITER + oparg + 1;
assert(_PyCode_CODE(code)[target-1].op.code == END_FOR ||
_PyCode_CODE(code)[target-1].op.code == INSTRUMENTED_END_FOR);
}
}
break;
case OPARG_CACHE_1:
Expand Down

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