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GH-100982: Restrict FOR_ITER_RANGE to a single instruction to allow instrumentation. #101985

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Merged
merged 2 commits into from
Feb 22, 2023
Merged

GH-100982: Restrict FOR_ITER_RANGE to a single instruction to allow instrumentation. #101985

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Restrict FOR_ITER_RANGE to a single instruction to allow instrumentat…
markshannon Feb 17, 2023
46593a5
Merge branch 'main' into restrict-for-iter-specializations-to-one-ins…
markshannon Feb 20, 2023
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2023-02-17-10-12-13.gh-issue-100982.mJGJQw.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Restrict the scope of the :opcode:`FOR_ITER_RANGE` instruction to the scope of the
original :opcode:`FOR_ITER` instruction, to allow instrumentation.
24 changes: 8 additions & 16 deletions Python/bytecodes.c
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Expand Up @@ -2178,35 +2178,27 @@ dummy_func(
// Common case: no jump, leave it to the code generator
}

// 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)) {
inst(FOR_ITER_RANGE, (unused/1, iter -- iter, next)) {
assert(cframe.use_tracing == 0);
_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[next.op.code] == 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);
DISPATCH();
}
else {
long value = r->start;
r->start = value + r->step;
r->len--;
if (_PyLong_AssignValue(&GETLOCAL(next.op.arg), value) < 0) {
goto error;
}
// The STORE_FAST is already done.
JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + 1);
long value = r->start;
r->start = value + r->step;
r->len--;
next = PyLong_FromLong(value);
if (next == NULL) {
goto error;
}
DISPATCH();
}

// 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 *)iter;
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22 changes: 11 additions & 11 deletions Python/generated_cases.c.h
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4 changes: 1 addition & 3 deletions Python/specialize.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2155,8 +2155,6 @@ _Py_Specialize_ForIter(PyObject *iter, _Py_CODEUNIT *instr, int oparg)
assert(_PyOpcode_Caches[FOR_ITER] == INLINE_CACHE_ENTRIES_FOR_ITER);
_PyForIterCache *cache = (_PyForIterCache *)(instr + 1);
PyTypeObject *tp = Py_TYPE(iter);
_Py_CODEUNIT next = instr[1+INLINE_CACHE_ENTRIES_FOR_ITER];
int next_op = _PyOpcode_Deopt[next.op.code];
if (tp == &PyListIter_Type) {
instr->op.code = FOR_ITER_LIST;
goto success;
Expand All @@ -2165,7 +2163,7 @@ _Py_Specialize_ForIter(PyObject *iter, _Py_CODEUNIT *instr, int oparg)
instr->op.code = FOR_ITER_TUPLE;
goto success;
}
else if (tp == &PyRangeIter_Type && next_op == STORE_FAST) {
else if (tp == &PyRangeIter_Type) {
instr->op.code = FOR_ITER_RANGE;
goto success;
}
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