aio-libs / multidict / 37602143081

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Fold the self-extend and same-class update scans into their callers (#1731)

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## What do these changes do?

Folds `_md_extend_self_scan()` into `md_extend_self()` and
`_md_update_from_ht_scan()` into `md_update_from_ht()`. The self-extend
loop now reads the table kind at run time, so `d.extend(d)` gets one
copy instead of two. The same-class update loop also takes the kind at
run time, but GCC unswitches it on that invariant, so both
kind-specialised loops survive in `md_update_from_ht` (756 to 760
instructions) and `_multidict_bulk_locked` shrinks by 228 instructions.

The `_md_update_from_ht_scan` rule in `tools/check_inlining.py` is
removed with the helper. It guarded the constant kind that #1676
measured; the callgrind numbers below show `extend()`, `merge()` and
`update()` from another multidict unchanged without it.

## Are there changes in behavior for the user?

No.

## Is it a substantial burden for the maintainers to support this?

No, it removes two helpers.

## Related issue number

N/A

## Checklist

- [x] I think the code is well written
- [ ] Unit tests for the changes exist: N/A, refactor covered by the
existing suite
- [ ] Documentation reflects the changes: N/A
- [ ] If you provide code modification, please add yourself to
`CONTRIBUTORS.txt`: N/A
- [x] Add a new news fragment into the `CHANGES/` folder
- [x] `make doc-spelling` passes and any new technical words are added
to `docs/spelling_wordlist.txt`

Drafted with Claude Code (Claude Opus 5.5); reviewed by @asvetlov.

<details>
<summary>Agent run details (optional, for reviewers)</summary>

Tests, C extension, 3.10.17: 4093 passed, 177 skipped
Tests, C extension, 3.14.7t: 4074 passed, 196 skipped
Tests, pure Python (`MULTIDICT_NO_EXTENSIONS=1 ... --no-c-extensions`),
3.10.17: 1612 passed, 22 skipped
`tools/check_inlining.py` on 3.14.7 and 3.14.7t: ok, 19 and 21 rules
`make doc-spelling`: passed

Perf: callgrind, `PYTHONHASHSEED=0`, Ir per ... (continued)

793 of 1586 branches covered (50.0%)

Branch coverage included in aggregate %.

9353 of 10217 relevant lines covered (91.54%)

1.83 hits per line