New submission from STINNER Victor:
Argument Clinic calls one the following functions depending on parameters:
* PyArg_UnpackTuple(), _PyArg_UnpackStack()
* PyArg_ParseTuple(), _PyArg_ParseStack()
* PyArg_ParseTupleAndKeywords(), _PyArg_ParseStackAndKeywords()
* etc.
Would it make sense to emit C code instead of calling complex and slow
PyArg_ParseXXX() functions? It would emit the most efficient C code to parse
arguments.
I don't recall where this idea comes from. Maybe Larry Hastings told me once
that he wants to implement this idea :-) I'm sure that Larry has a big plan but
lacks time to implement all of his cool ideas.
Using profiled guided optimization (PGO), the compiler should be able to easily
detect that error cases are unlikely and mark these code paths as unlikely.
We should probably experiment an implementation to be able to measure the
speedup, to be able to say if the idea is worth it or not, in term of
performance, since the motivation here is clearly performance.
We can begin with format strings only made of "O" format. Most simple example
with divmod(), replace:
if (!_PyArg_UnpackStack(args, nargs, "divmod", 2, 2, &x, &y)) { return
NULL; }
with something like:
if (nargs != 2) { _PyArg_ErrNumArgs(nargs, 2, 2, "divmod"); return NULL; }
x = args[0];
y = args[1];
The next question is if we should go further with more complex formats. Example
with the format() function, replace:
if (!_PyArg_ParseStack(args, nargs, "O|U:format", &value, &format_spec)) {
... }
with:
if (nargs < 1 || nargs > 2) { _PyArg_ErrNumArgs(nargs, 1, 2, "format");
return NULL; }
value = args[0];
if (nargs == 2) {
format_spec = args[1];
if (!PyUnicode_Check(format_spec)) { .. raise an exception ...; return
NULL; }
/* getargs.c calls PyUnicode_READY(), we should also do it here */
if (PyUnicode_READY(format_spec) == -1) { return NULL; }
}
else {
format_spec = NULL;
}
----------
components: Argument Clinic
messages: 286778
nosy: haypo, inada.naoki, larry, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Argument Clinic: inline PyArg_UnpackTuple and
PyArg_ParseStack(AndKeyword)?
type: performance
versions: Python 3.7
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Python tracker <[email protected]>
<http://bugs.python.org/issue29419>
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