Document how to add a bytecode specialization

How to add a new bytecode specialization is knowledge only a few of us remember right now. We should document this somewhere (devguide or CPython, I don't mind). Hopefully a new contributor can pick this up!

There reference is this PR: https://github.com/python/cpython/pull/116385/files

Assuming you found an instruction that serves as a good specialization candidate. Let's use the example of CONTAINS_OP:

1. Set the original CONTAINS_OP to a uop by changing it from CONTAINS_OP to _CONTAINS_OP in Python/bytecodes.c. The instruction definition should also change from inst to op.
2. Add the uop that calls a specializing function. In this case _SPECIALIZE_CONTAINS_OP.
3. The original CONTAINS_OP is now a new macro consisting of _SPECIALIZE_CONTAINS_OP + _CONTAINS_OP.
4. Define the cache structure in Include/internal/pycore_code.h. At the very least, a 16-bit counter is needed.
5. Write the specializing function itself in Python/specialize.c. Refer to any other function in that file for the format.
6. Remember to update operation stats by calling add_stat_dict in Python/specialize.c.
7. Add the cache layout in Lib/opcode.py so that Python's dis module will know how to represent it properly.
8. Bump magic number in Include/internal/pycore_magic_number.h.
9. Run make regen-all on *nix or build.bat --regen on PC.

Utilisez PR 116385 et le plan en neuf étapes comme sources de référence. Commencez par examiner les modifications référencées et les fichiers indiqués—Python/bytecodes.c, Include/internal/pycore_code.h, Python/specialize.c, Lib/opcode.py et Include/internal/pycore_magic_number.h—puis choisissez l’emplacement approprié dans la devguide ou la documentation de CPython. Le travail est terminé lorsqu’une personne débutante peut suivre le workflow de spécialisation et le vérifier avec make regen-all ou build.bat --regen.