LOAD_FAST_BORROWED optimization can be missed after an empty block

[DinoV]

Bug report

Bug description:

def x(tz_str):
    try:
        start, end = 1, 2
    except ValueError as e:
        raise Exception()

    return f(start, end)

This should produce a LOAD_FAST_BORROWED_LOAD_FAST_BORROWED opcode for loading start and end, but instead it produces LOAD_FAST_LOAD_FAST

CPython versions tested on:

3.14, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-138250: load fast optimization should fall through to empty blocks #138249

[itamaro]

should this get backported to 3.14? (maybe 3.14.1 if it's not critical?)

[DinoV]

should this get backported to 3.14? (maybe 3.14.1 if it's not critical?)

I asked @mpage what he thought when I found it and he didn't think it'd be worth it. There should be no behavioral changes and the performance cost is probably not too frequent.