gh-125442: Use _PyLong_GetOne() and _PyLong_GetZero() in Objects

[hikariyo]

Simply reduces a null check as _PyLong_GetOne() cannot fail.

• Issue: Use _PyLong_GetOne() and _PyLong_GetZero() in Objects #125442

[ghost]

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[skirpichev]

There are other places, that might be changed, especially in longobject.c:

$ git grep 'PyLong_From[IL].*([10]' Objects/|wc -l
22

I suggest you first create an issue.

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

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[serhiy-storchaka]

Do not merge until there are solid evidences of the speed up.

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[skirpichev]

@serhiy-storchaka, why do you suspect speed regressions at all? PyLong_FromLong() will run more complex versions of _PyLong_GetZero/One anyway.

cpython/Objects/longobject.c

Lines 309 to 317 in 5dac0dc

	PyLong_FromLong(long ival)
	{
	PyLongObject *v;
	unsigned long abs_ival, t;
	int ndigits;
	/* Handle small and medium cases. */
	if (IS_SMALL_INT(ival)) {
	return get_small_int((sdigit)ival);

cpython/Objects/longobject.c

Lines 56 to 61 in 5dac0dc

	static PyObject *
	get_small_int(sdigit ival)
	{
	assert(IS_SMALL_INT(ival));
	return (PyObject *)&_PyLong_SMALL_INTS[_PY_NSMALLNEGINTS + ival];
	}

cpython/Include/internal/pycore_long.h

Lines 66 to 74 in 5dac0dc

	// Return a reference to the immortal zero singleton.
	// The function cannot return NULL.
	static inline PyObject* _PyLong_GetZero(void)
	{ return (PyObject *)&_PyLong_SMALL_INTS[_PY_NSMALLNEGINTS]; }
	// Return a reference to the immortal one singleton.
	// The function cannot return NULL.
	static inline PyObject* _PyLong_GetOne(void)
	{ return (PyObject *)&_PyLong_SMALL_INTS[_PY_NSMALLNEGINTS+1]; }

[hikariyo]

@serhiy-storchaka I'm inspired by #125044 and I found that there are other places using PyLong_FromLong for 0 or 1.

At least the 2 null checks below should be removed. They're unreachable.

cpython/Objects/floatobject.c

Lines 1564 to 1566 in 5dac0dc

	denominator = PyLong_FromLong(1);
	if (denominator == NULL)
	goto error;

cpython/Objects/longobject.c

Lines 5006 to 5008 in 5dac0dc

	z = (PyLongObject *)PyLong_FromLong(1L);
	if (z == NULL)
	goto Error;

[skirpichev]

@hikariyo, all similar checks are unreachable now. But that's might be viewed as internal detail of the PyLong_FromLong() implementation.

[serhiy-storchaka]

I suspect no difference at all. This is a pure cosmetic change. On other hand, it replaces public functions calls with private functions calls. So, this is a cosmetic change that makes the code more ugly.

[hikariyo]

@hikariyo, all similar checks are unreachable now. But that's might be viewed as internal detail of te PyLong_FromLong() implementation.

However _PyLong_GetZero/One must return non-null values, so using them can avoid this problem.

[hikariyo]

I suspect no difference at all. This is a pure cosmetic change. On other hand, it replaces public functions calls with private functions calls. So, this is a cosmetic change that makes the code more ugly.

But _PyLong_GetZero/One do widely used in current code. Shouldn't we unify the usages?

[serhiy-storchaka]

They were introduced (first as simple global variables) for the cases when you need a borrowed reference to integers 0 or 1. PyLong_FromLong() continued to be used in cases when you need a new reference.

Closing this PR as pure cosmetic change.