Avoid temporary varargs tuple creation in argument passing

colorfulappl · Dec 31, 2021 · Dec 31, 2021 · Jan 4, 2022 · Jan 4, 2022 · Jan 4, 2022
commit b68176d081e19a3cedbaf2cdb31ecd7690421ec8
diff --git a/Include/modsupport.h b/Include/modsupport.h
@@ -134,7 +134,8 @@ PyAPI_FUNC(PyObject * const *) _PyArg_UnpackKeywordsWithVararg(
         PyObject *kwargs, PyObject *kwnames,
         struct _PyArg_Parser *parser,
         int minpos, int maxpos, int minkw,
-        int vararg, PyObject **buf);
+        int vararg, Py_ssize_t varargssize,
+        PyObject **buf);
 
 #define _PyArg_UnpackKeywords(args, nargs, kwargs, kwnames, parser, minpos, maxpos, minkw, buf) \
     (((minkw) == 0 && (kwargs) == NULL && (kwnames) == NULL && \

diff --git a/Lib/test/clinic.test b/Lib/test/clinic.test
@@ -3324,14 +3324,15 @@ PyDoc_STRVAR(test_vararg_and_posonly__doc__,
     {"test_vararg_and_posonly", (PyCFunction)(void(*)(void))test_vararg_and_posonly, METH_FASTCALL, test_vararg_and_posonly__doc__},
 
 static PyObject *
-test_vararg_and_posonly_impl(PyObject *module, PyObject *a, PyObject *args);
+test_vararg_and_posonly_impl(PyObject *module, PyObject *a,
+                             Py_ssize_t varargssize, PyObject *const *args);
 
 static PyObject *
 test_vararg_and_posonly(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     PyObject *a;
-    PyObject *__clinic_args = NULL;
+    PyObject *const *__clinic_args = NULL;
 
     if (!_PyArg_CheckPositional("test_vararg_and_posonly", nargs, 1, PY_SSIZE_T_MAX)) {
         goto exit;
@@ -3341,16 +3342,16 @@ test_vararg_and_posonly(PyObject *module, PyObject *const *args, Py_ssize_t narg
     for (Py_ssize_t i = 0; i < nargs - 1; ++i) {
         PyTuple_SET_ITEM(__clinic_args, i, args[1 + i]);
     }
-    return_value = test_vararg_and_posonly_impl(module, a, __clinic_args);
+    return_value = test_vararg_and_posonly_impl(module, a, varargssize, __clinic_args);
 
 exit:
-    Py_XDECREF(__clinic_args);
     return return_value;
 }
 
 static PyObject *
-test_vararg_and_posonly_impl(PyObject *module, PyObject *a, PyObject *args)
-/*[clinic end generated code: output=ada613d2d87c9341 input=08dc2bf7afbf1613]*/
+test_vararg_and_posonly_impl(PyObject *module, PyObject *a,
+                             Py_ssize_t varargssize, PyObject *const *args)
+/*[clinic end generated code: output=6a6c69c6ff7deb9b input=08dc2bf7afbf1613]*/
 
 /*[clinic input]
 test_vararg
@@ -3370,7 +3371,8 @@ PyDoc_STRVAR(test_vararg__doc__,
     {"test_vararg", (PyCFunction)(void(*)(void))test_vararg, METH_FASTCALL|METH_KEYWORDS, test_vararg__doc__},
 
 static PyObject *
-test_vararg_impl(PyObject *module, PyObject *a, PyObject *args);
+test_vararg_impl(PyObject *module, PyObject *a, Py_ssize_t varargssize,
+                 PyObject *const *args);
 
 static PyObject *
 test_vararg(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
@@ -3379,26 +3381,27 @@ test_vararg(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject
     static const char * const _keywords[] = {"a", NULL};
     static _PyArg_Parser _parser = {NULL, _keywords, "test_vararg", 0};
     PyObject *argsbuf[2];
+    Py_ssize_t varargssize = Py_MAX(nargs - 1, 0);
     Py_ssize_t noptargs = 0 + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *a;
-    PyObject *__clinic_args = NULL;
+    PyObject *const *__clinic_args = NULL;
 
-    args = _PyArg_UnpackKeywordsWithVararg(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, 1, argsbuf);
+    args = _PyArg_UnpackKeywordsWithVararg(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, 1, varargssize, argsbuf);
     if (!args) {
         goto exit;
     }
     a = args[0];
-    __clinic_args = args[1];
-    return_value = test_vararg_impl(module, a, __clinic_args);
+    __clinic_args = (PyObject *const *)args[1];
+    return_value = test_vararg_impl(module, a, varargssize, __clinic_args);
 
 exit:
-    Py_XDECREF(__clinic_args);
     return return_value;
 }
 
 static PyObject *
-test_vararg_impl(PyObject *module, PyObject *a, PyObject *args)
-/*[clinic end generated code: output=f721025731c3bfe8 input=81d33815ad1bae6e]*/
+test_vararg_impl(PyObject *module, PyObject *a, Py_ssize_t varargssize,
+                 PyObject *const *args)
+/*[clinic end generated code: output=9f3d65086405e9b6 input=81d33815ad1bae6e]*/
 
 /*[clinic input]
 test_vararg_with_default
@@ -3419,7 +3422,8 @@ PyDoc_STRVAR(test_vararg_with_default__doc__,
     {"test_vararg_with_default", (PyCFunction)(void(*)(void))test_vararg_with_default, METH_FASTCALL|METH_KEYWORDS, test_vararg_with_default__doc__},
 
 static PyObject *
-test_vararg_with_default_impl(PyObject *module, PyObject *a, PyObject *args,
+test_vararg_with_default_impl(PyObject *module, PyObject *a,
+                              Py_ssize_t varargssize, PyObject *const *args,
                               int b);
 
 static PyObject *
@@ -3429,17 +3433,18 @@ test_vararg_with_default(PyObject *module, PyObject *const *args, Py_ssize_t nar
     static const char * const _keywords[] = {"a", "b", NULL};
     static _PyArg_Parser _parser = {NULL, _keywords, "test_vararg_with_default", 0};
     PyObject *argsbuf[3];
+    Py_ssize_t varargssize = Py_MAX(nargs - 1, 0);
     Py_ssize_t noptargs = 0 + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *a;
-    PyObject *__clinic_args = NULL;
+    PyObject *const *__clinic_args = NULL;
     int b = 0;
 
-    args = _PyArg_UnpackKeywordsWithVararg(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, 1, argsbuf);
+    args = _PyArg_UnpackKeywordsWithVararg(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, 1, varargssize, argsbuf);
     if (!args) {
         goto exit;
     }
     a = args[0];
-    __clinic_args = args[1];
+    __clinic_args = (PyObject *const *)args[1];
     if (!noptargs) {
         goto skip_optional_kwonly;
     }
@@ -3448,17 +3453,17 @@ test_vararg_with_default(PyObject *module, PyObject *const *args, Py_ssize_t nar
         goto exit;
     }
 skip_optional_kwonly:
-    return_value = test_vararg_with_default_impl(module, a, __clinic_args, b);
+    return_value = test_vararg_with_default_impl(module, a, varargssize, __clinic_args, b);
 
 exit:
-    Py_XDECREF(__clinic_args);
     return return_value;
 }
 
 static PyObject *
-test_vararg_with_default_impl(PyObject *module, PyObject *a, PyObject *args,
+test_vararg_with_default_impl(PyObject *module, PyObject *a,
+                              Py_ssize_t varargssize, PyObject *const *args,
                               int b)
-/*[clinic end generated code: output=63b34d3241c52fda input=6e110b54acd9b22d]*/
+/*[clinic end generated code: output=711a606d86d09fec input=6e110b54acd9b22d]*/
 
 /*[clinic input]
 test_vararg_with_only_defaults
@@ -3479,7 +3484,8 @@ PyDoc_STRVAR(test_vararg_with_only_defaults__doc__,
     {"test_vararg_with_only_defaults", (PyCFunction)(void(*)(void))test_vararg_with_only_defaults, METH_FASTCALL|METH_KEYWORDS, test_vararg_with_only_defaults__doc__},
 
 static PyObject *
-test_vararg_with_only_defaults_impl(PyObject *module, PyObject *args, int b,
+test_vararg_with_only_defaults_impl(PyObject *module, Py_ssize_t varargssize,
+                                    PyObject *const *args, int b,
                                     PyObject *c);
 
 static PyObject *
@@ -3489,16 +3495,17 @@ test_vararg_with_only_defaults(PyObject *module, PyObject *const *args, Py_ssize
     static const char * const _keywords[] = {"b", "c", NULL};
     static _PyArg_Parser _parser = {NULL, _keywords, "test_vararg_with_only_defaults", 0};
     PyObject *argsbuf[3];
+    Py_ssize_t varargssize = Py_MAX(nargs - 0, 0);
     Py_ssize_t noptargs = 0 + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 0;
-    PyObject *__clinic_args = NULL;
+    PyObject *const *__clinic_args = NULL;
     int b = 0;
     PyObject *c = " ";
 
-    args = _PyArg_UnpackKeywordsWithVararg(args, nargs, NULL, kwnames, &_parser, 0, 0, 0, 0, argsbuf);
+    args = _PyArg_UnpackKeywordsWithVararg(args, nargs, NULL, kwnames, &_parser, 0, 0, 0, 0, varargssize, argsbuf);
     if (!args) {
         goto exit;
     }
-    __clinic_args = args[0];
+    __clinic_args = (PyObject *const *)args[0];
     if (!noptargs) {
         goto skip_optional_kwonly;
     }
@@ -3513,14 +3520,14 @@ test_vararg_with_only_defaults(PyObject *module, PyObject *const *args, Py_ssize
     }
     c = args[2];
 skip_optional_kwonly:
-    return_value = test_vararg_with_only_defaults_impl(module, __clinic_args, b, c);
+    return_value = test_vararg_with_only_defaults_impl(module, varargssize, __clinic_args, b, c);
 
 exit:
-    Py_XDECREF(__clinic_args);
     return return_value;
 }
 
 static PyObject *
-test_vararg_with_only_defaults_impl(PyObject *module, PyObject *args, int b,
+test_vararg_with_only_defaults_impl(PyObject *module, Py_ssize_t varargssize,
+                                    PyObject *const *args, int b,
                                     PyObject *c)
-/*[clinic end generated code: output=dc29ce6ebc2ec10c input=fa56a709a035666e]*/
+/*[clinic end generated code: output=f1415a05ea48fc50 input=fa56a709a035666e]*/
diff --git a/Python/getargs.c b/Python/getargs.c
@@ -2470,11 +2470,11 @@ _PyArg_UnpackKeywordsWithVararg(PyObject *const *args, Py_ssize_t nargs,
                                 PyObject *kwargs, PyObject *kwnames,
                                 struct _PyArg_Parser *parser,
                                 int minpos, int maxpos, int minkw,
-                                int vararg, PyObject **buf)
+                                int vararg, Py_ssize_t varargssize,
+                                PyObject **buf)
 {
     PyObject *kwtuple;
     PyObject *keyword;
-    Py_ssize_t varargssize = 0;
     int i, posonly, minposonly, maxargs;
     int reqlimit = minkw ? maxpos + minkw : minpos;
     Py_ssize_t nkwargs;
@@ -2529,26 +2529,12 @@ _PyArg_UnpackKeywordsWithVararg(PyObject *const *args, Py_ssize_t nargs,
         return NULL;
     }
 
-    /* create varargs tuple */
-    varargssize = nargs - maxpos;
-    if (varargssize < 0) {
-        varargssize = 0;
-    }
-    buf[vararg] = PyTuple_New(varargssize);
-    if (!buf[vararg]) {
-        return NULL;
-    }
+    /* pass varargs by pointer */
+    buf[vararg] = (PyObject *)&args[vararg];
 
-    /* copy tuple args */
-    for (i = 0; i < nargs; i++) {
-        if (i >= vararg) {
-            Py_INCREF(args[i]);
-            PyTuple_SET_ITEM(buf[vararg], i - vararg, args[i]);
-            continue;
-        }
-        else {
+    /* copy required positional args */
+    for (i = 0; i < vararg; i++) {
             buf[i] = args[i];
-        }
     }
 
     /* copy keyword args using kwtuple to drive process */

@@ -942,7 +942,7 @@ def parser_body(prototype, *fields, declarations=''):
                     min_kw_only
                 )
             else:
-                args_declaration = "_PyArg_UnpackKeywordsWithVararg", "%s, %s, %s, %s" % (
+                args_declaration = "_PyArg_UnpackKeywordsWithVararg", "%s, %s, %s, %s, varargssize" % (
                     min_pos,
                     max_pos,
                     min_kw_only,
@@ -957,6 +957,8 @@ def parser_body(prototype, *fields, declarations=''):
                     static _PyArg_Parser _parser = {{NULL, _keywords, "{name}", 0}};
                     PyObject *argsbuf[%s];
                     """ % len(converters))
+                if vararg != NO_VARARG:
+                    declarations += "\nPy_ssize_t varargssize = Py_MAX(nargs - %d, 0);" % (max_pos)
                 if has_optional_kw:
                     pre_buffer = "0" if vararg != NO_VARARG else "nargs"
                     declarations += "\nPy_ssize_t noptargs = %s + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - %d;" % (pre_buffer, min_pos + min_kw_only)
@@ -994,6 +996,8 @@ def parser_body(prototype, *fields, declarations=''):
             add_label = None
             for i, p in enumerate(parameters):
                 displayname = p.get_displayname(i+1)
+                if p.is_vararg():
+                    p.converter.type = 'PyObject *const *'
                 parsearg = p.converter.parse_arg(argname_fmt % i, displayname)
                 if parsearg is None:
                     #print('Cannot convert %s %r for %s' % (p.converter.__class__.__name__, p.converter.format_unit, p.converter.name), file=sys.stderr)
@@ -1305,9 +1309,6 @@ def render_function(self, clinic, f):
             if (i != -1) and (p.default is not unspecified):
                 first_optional = min(first_optional, i)
 
-            if p.is_vararg():
-                data.cleanup.append("Py_XDECREF({});".format(c.parser_name))
-
             # insert group variable
             group = p.group
             if last_group != group:
@@ -1319,6 +1320,11 @@ def render_function(self, clinic, f):
                     data.impl_parameters.append("int " + group_name)
                     has_option_groups = True
 
+            if p.is_vararg():
+                p.converter.type = 'PyObject *const *'
+                data.impl_arguments.append('varargssize')
+                data.impl_parameters.append('Py_ssize_t varargssize')
+
             c.render(p, data)
 
         if has_option_groups and (not positional):