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GH-98831: Add DECREF_INPUTS(), expanding to DECREF() each stack input #100205

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Merged
gvanrossum merged 1 commit into from
Dec 17, 2022
Merged

GH-98831: Add DECREF_INPUTS(), expanding to DECREF() each stack input #100205

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Add DECREF_INPUTS(), expanding to DECREF() each stack input 
The presence of this macro indicates that a particular instruction
may be considered for conversion to a register-based format
(see faster-cpython/ideas#485).

An invariant (currently unchecked) is that `DEOPT_IF()` may only
occur *before* `DECREF_INPUTS()`, and `ERROR_IF()` may only occur
*after* it. One reason not to check this is that there are a few
places where we insert *two* `DECREF_INPUTS()` calls, in different
branches of the code. The invariant checking would have to be able
to do some flow control analysis to understand this.

Note that many instructions, especially specialized ones,
can't be converted to use this macro straightforwardly.
This is because the generator currently only generates plain
`Py_DECREF(variable)` statements, and cannot generate
things like `_Py_DECREF_SPECIALIZED()` let alone deal with
`_PyList_AppendTakeRef()`.
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@gvanrossum
gvanrossum committed Dec 13, 2022
commit beaea6105cdb4e3c96ba313dc5d211b644ef0e1c
31 changes: 13 additions & 18 deletions Python/bytecodes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -161,7 +161,7 @@ dummy_func(
super(LOAD_CONST__LOAD_FAST) = LOAD_CONST + LOAD_FAST;

inst(POP_TOP, (value --)) {
Py_DECREF(value);
DECREF_INPUTS();
}

inst(PUSH_NULL, (-- res)) {
Expand All @@ -172,19 +172,19 @@ dummy_func(

inst(UNARY_POSITIVE, (value -- res)) {
res = PyNumber_Positive(value);
Py_DECREF(value);
DECREF_INPUTS();
ERROR_IF(res == NULL, error);
}

inst(UNARY_NEGATIVE, (value -- res)) {
res = PyNumber_Negative(value);
Py_DECREF(value);
DECREF_INPUTS();
ERROR_IF(res == NULL, error);
}

inst(UNARY_NOT, (value -- res)) {
int err = PyObject_IsTrue(value);
Py_DECREF(value);
DECREF_INPUTS();
ERROR_IF(err < 0, error);
if (err == 0) {
res = Py_True;
Expand All @@ -197,7 +197,7 @@ dummy_func(

inst(UNARY_INVERT, (value -- res)) {
res = PyNumber_Invert(value);
Py_DECREF(value);
DECREF_INPUTS();
ERROR_IF(res == NULL, error);
}

Expand Down Expand Up @@ -351,8 +351,7 @@ dummy_func(
STAT_INC(BINARY_SUBSCR, deferred);
DECREMENT_ADAPTIVE_COUNTER(cache->counter);
res = PyObject_GetItem(container, sub);
Py_DECREF(container);
Py_DECREF(sub);
DECREF_INPUTS();
ERROR_IF(res == NULL, error);
}

Expand Down Expand Up @@ -438,8 +437,7 @@ dummy_func(
ERROR_IF(true, error);
}
Py_INCREF(res); // Do this before DECREF'ing dict, sub
Py_DECREF(dict);
Py_DECREF(sub);
DECREF_INPUTS();
}

inst(BINARY_SUBSCR_GETITEM, (unused/1, type_version/2, func_version/1, container, sub -- unused)) {
Expand Down Expand Up @@ -500,9 +498,7 @@ dummy_func(
DECREMENT_ADAPTIVE_COUNTER(cache->counter);
/* container[sub] = v */
int err = PyObject_SetItem(container, sub, v);
Py_DECREF(v);
Py_DECREF(container);
Py_DECREF(sub);
DECREF_INPUTS();
ERROR_IF(err, error);
}

Expand Down Expand Up @@ -538,8 +534,7 @@ dummy_func(
inst(DELETE_SUBSCR, (container, sub --)) {
/* del container[sub] */
int err = PyObject_DelItem(container, sub);
Py_DECREF(container);
Py_DECREF(sub);
DECREF_INPUTS();
ERROR_IF(err, error);
}

Expand All @@ -550,11 +545,11 @@ dummy_func(
if (hook == NULL) {
_PyErr_SetString(tstate, PyExc_RuntimeError,
"lost sys.displayhook");
Py_DECREF(value);
DECREF_INPUTS();
ERROR_IF(true, error);
}
res = PyObject_CallOneArg(hook, value);
Py_DECREF(value);
DECREF_INPUTS();
ERROR_IF(res == NULL, error);
Py_DECREF(res);
}
Expand Down Expand Up @@ -625,12 +620,12 @@ dummy_func(
"'async for' requires an object with "
"__aiter__ method, got %.100s",
type->tp_name);
Py_DECREF(obj);
DECREF_INPUTS();
ERROR_IF(true, error);
}

iter = (*getter)(obj);
Py_DECREF(obj);
DECREF_INPUTS();
ERROR_IF(iter == NULL, error);

if (Py_TYPE(iter)->tp_as_async == NULL ||
Expand Down
6 changes: 5 additions & 1 deletion Tools/cases_generator/generate_cases.py
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Original file line number Diff line number Diff line change
Expand Up @@ -209,7 +209,7 @@ def write_body(self, out: Formatter, dedent: int, cache_adjust: int = 0) -> None
cache_offset += ceffect.size
assert cache_offset == self.cache_offset + cache_adjust

# Write the body, substituting a goto for ERROR_IF()
# Write the body, substituting a goto for ERROR_IF() and other stuff
assert dedent <= 0
extra = " " * -dedent
for line in self.block_text:
Expand All @@ -232,6 +232,10 @@ def write_body(self, out: Formatter, dedent: int, cache_adjust: int = 0) -> None
)
else:
out.write_raw(f"{extra}{space}if ({cond}) goto {label};\n")
elif m := re.match(r"(\s*)DECREF_INPUTS\(\);\s*$", line):
space = m.group(1)
for ieff in self.input_effects:
out.write_raw(f"{extra}{space}Py_DECREF({ieff.name});\n")
else:
out.write_raw(extra + line)

Expand Down