[issue29358] Add tp_fastnew and tp_fastinit to PyTypeObject, 15-20% faster object instanciation

[STINNER Victor]

STINNER Victor added the comment:

While they are obvious speedup on microbenchmarks, it doesn't speedup "macro" benchmarks from performance as much as I expected.

The changes required in typeobject.c to support "tp_new or tp_fastnew" and "tp_init or tp_fastinit" are large and very complex. I'm not sure that my code is correct. update_one_slot(), add_operators() and PyType_Ready() functions are complex beast, sadly almost not documented, except such comment...

            /* The __new__ wrapper is not a wrapper descriptor,
               so must be special-cased differently.
               If we don't do this, creating an instance will
               always use slot_tp_new which will look up
               __new__ in the MRO which will call tp_new_wrapper
               which will look through the base classes looking
               for a static base and call its tp_new (usually
               PyType_GenericNew), after performing various
               sanity checks and constructing a new argument
               list.  Cut all that nonsense short -- this speeds
               up instance creation tremendously. */
            specific = (void *)type->tp_new;
            /* XXX I'm not 100% sure that there isn't a hole
               in this reasoning that requires additional
               sanity checks.  I'll buy the first person to
               point out a bug in this reasoning a beer. */

How am I supposed to be confident in front of such coment :-D

I expect that calling a functions (tp_call) is a more common operation than instanciating a new object (tp_new + tp_init). So I don't think that the overall change is worth it.

For all these reaons, I close the issue as REJECTED.

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resolution:  -> rejected
status: open -> closed

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29358>
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