Shaw: Python 3.13 gets a JIT

Anthony Shaw describesthe new copy-and-patch JIT that has been proposed for Python 3.13.

Copy-and-patch was selected because the compilation from bytecodesto machine code is done as a set of templates" that are thenstitched together and patched at runtime with the correctvalues. This means that your average Python user isn't running thiscomplex JIT compiler architecture inside their Pythonruntime. Python writing it's own IL and JIT would also beunreasonable since so many are available off-the-shelf like LLVMsand ryuJIT. But a full-JIT would require those being bundled withPython and all the added overheads. A copy-and-patch JIT onlyrequires the LLVM JIT tools be installed on the machine whereCPython is compiled from source, and for most people that means themachines of the CI that builds and packages CPython for python.org.