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bpo-40521: Optimize PyUnicode_New(0, maxchar) #21099

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Jun 23, 2020
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bpo-40521: Optimize PyUnicode_New(0, maxchar) #21099

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80 changes: 25 additions & 55 deletions Objects/unicodeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -231,28 +231,19 @@ get_unicode_state(void)


// Return a borrowed reference to the empty string singleton.
// Return NULL if the singleton was not created yet.
static inline PyObject* unicode_get_empty(void)
{
struct _Py_unicode_state *state = get_unicode_state();
// unicode_get_empty() must not be called before _PyUnicode_Init()
// or after _PyUnicode_Fini()
assert(state->empty != NULL);
return state->empty;
}

static inline PyObject* unicode_new_empty(void)
{
struct _Py_unicode_state *state = get_unicode_state();
PyObject *empty = state->empty;
if (empty != NULL) {
Py_INCREF(empty);
}
else {
empty = PyUnicode_New(0, 0);
if (empty != NULL) {
Py_INCREF(empty);
assert(_PyUnicode_CheckConsistency(empty, 1));
state->empty = empty;
}
}
PyObject *empty = unicode_get_empty();
Py_INCREF(empty);
return empty;
}

Expand Down Expand Up @@ -696,12 +687,9 @@ unicode_result_ready(PyObject *unicode)
PyObject *empty = unicode_get_empty();
if (unicode != empty) {
Py_DECREF(unicode);

Py_INCREF(empty);
return empty;
}
// unicode is the empty string singleton
return unicode;
return empty;
}

#ifdef LATIN1_SINGLETONS
Expand Down Expand Up @@ -959,7 +947,7 @@ ensure_unicode(PyObject *obj)

/* Compilation of templated routines */

#define STRINGLIB_GET_EMPTY() unicode_get_empty()
#define STRINGLIB_GET_EMPTY() unicode_get_empty()

#include "stringlib/asciilib.h"
#include "stringlib/fastsearch.h"
Expand Down Expand Up @@ -1260,11 +1248,7 @@ _PyUnicode_New(Py_ssize_t length)

/* Optimization for empty strings */
if (length == 0) {
PyObject *empty = unicode_get_empty();
if (empty != NULL) {
Py_INCREF(empty);
return (PyUnicodeObject *)empty;
}
return (PyUnicodeObject *)unicode_new_empty();
}

/* Ensure we won't overflow the size. */
Expand Down Expand Up @@ -1416,11 +1400,7 @@ PyUnicode_New(Py_ssize_t size, Py_UCS4 maxchar)
{
/* Optimization for empty strings */
if (size == 0) {
PyObject *empty = unicode_get_empty();
if (empty != NULL) {
Py_INCREF(empty);
return empty;
}
return unicode_new_empty();
}

PyObject *obj;
Expand Down Expand Up @@ -2001,8 +1981,7 @@ unicode_dealloc(PyObject *unicode)
static int
unicode_is_singleton(PyObject *unicode)
{
struct _Py_unicode_state *state = get_unicode_state();
if (unicode == state->empty) {
if (unicode == unicode_get_empty()) {
return 1;
}
#ifdef LATIN1_SINGLETONS
Expand Down Expand Up @@ -2059,8 +2038,6 @@ unicode_resize(PyObject **p_unicode, Py_ssize_t length)

if (length == 0) {
PyObject *empty = unicode_new_empty();
if (!empty)
return -1;
Py_SETREF(*p_unicode, empty);
return 0;
}
Expand Down Expand Up @@ -10868,10 +10845,7 @@ replace(PyObject *self, PyObject *str1,
}
new_size = slen + n * (len2 - len1);
if (new_size == 0) {
PyObject *empty = unicode_new_empty();
if (!empty)
goto error;
u = empty;
u = unicode_new_empty();
goto done;
}
if (new_size > (PY_SSIZE_T_MAX / rkind)) {
Expand Down Expand Up @@ -13293,13 +13267,7 @@ PyUnicode_Partition(PyObject *str_obj, PyObject *sep_obj)
len2 = PyUnicode_GET_LENGTH(sep_obj);
if (kind1 < kind2 || len1 < len2) {
PyObject *empty = unicode_get_empty(); // Borrowed reference
if (!empty) {
out = NULL;
}
else {
out = PyTuple_Pack(3, str_obj, empty, empty);
}
return out;
return PyTuple_Pack(3, str_obj, empty, empty);
}
buf1 = PyUnicode_DATA(str_obj);
buf2 = PyUnicode_DATA(sep_obj);
Expand Down Expand Up @@ -13351,13 +13319,7 @@ PyUnicode_RPartition(PyObject *str_obj, PyObject *sep_obj)
len2 = PyUnicode_GET_LENGTH(sep_obj);
if (kind1 < kind2 || len1 < len2) {
PyObject *empty = unicode_get_empty(); // Borrowed reference
if (!empty) {
out = NULL;
}
else {
out = PyTuple_Pack(3, empty, empty, str_obj);
}
return out;
return PyTuple_Pack(3, empty, empty, str_obj);
}
buf1 = PyUnicode_DATA(str_obj);
buf2 = PyUnicode_DATA(sep_obj);
Expand Down Expand Up @@ -15589,12 +15551,20 @@ _PyUnicode_Init(PyThreadState *tstate)
0x2029, /* PARAGRAPH SEPARATOR */
};

/* Init the implementation */
PyObject *empty = unicode_new_empty();
if (!empty) {
// Use size=1 rather than size=0, so PyUnicode_New(0, maxchar) can be
// optimized to always use state->empty without having to check if it is
// NULL or not.
PyObject *empty = PyUnicode_New(1, 0);
if (empty == NULL) {
return _PyStatus_NO_MEMORY();
}
Py_DECREF(empty);
PyUnicode_1BYTE_DATA(empty)[0] = 0;
_PyUnicode_LENGTH(empty) = 0;
assert(_PyUnicode_CheckConsistency(empty, 1));

struct _Py_unicode_state *state = &tstate->interp->unicode;
assert(state->empty == NULL);
state->empty = empty;

if (_Py_IsMainInterpreter(tstate)) {
/* initialize the linebreak bloom filter */
Expand Down