aio-libs / multidict / 37770274933

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Mark the error-raising helpers COLD (#1749)

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## What do these changes do?

Marks the nine error-raising helpers from #1667 `COLD`:
`_err_version_changed`, `_err_key_type_cs`, `_err_key_type_ci`, the
three `parse2` `_raise_*` helpers, and `_err_not_sequence`,
`_err_bad_length` and `_err_cannot_fetch`. Once #1739 dropped
`NOINLINE`, they became plain `static`, and GCC's early inliner put them
back into every caller. `_err_version_changed` was being inlined into
eight sites through `md_check_version()`, including the iterator step.
`COLD` is `cold, noinline`, so the helpers move out of line again
without bringing back `NOINLINE`.

Callgrind, rows that moved by 0.5% or more (all other rows flat):

| Build | Row | Before | After | Change |
|---|---|---|---|---|
| GIL | MultiDict `getitem_istr` | 767.0 | 736.0 | -4.04% |
| GIL | MultiDict `setitem_istr` | 896.0 | 891.1 | -0.55% |
| GIL | MultiDict `getitem_hit` | 164.0 | 165.0 | +0.61% |
| GIL | CIMultiDict `getall` | 916.8 | 921.5 | +0.51% |
| GIL | MultiDict / CIMultiDict `iter_keys` | 47.1 / 50.1 | 48.1 / 51.1
| +1 Ir per item |
| FT | CIMultiDict `delitem` | 483.8 | 477.8 | -1.24% |
| FT | CIMultiDict `ctor_items`, `reinit_items`, `ctor_small`,
`reinit_items_small` | | | -0.69% to -0.75% |
| FT | CIMultiDict `update`, `setitem_replace`, `getall` | | | -0.53% to
-0.57% |
| FT | MultiDict `delitem` | 405.8 | 402.8 | -0.74% |
| FT | MultiDict / CIMultiDict `iter_keys` | 83.9 / 86.9 | 84.8 / 87.8 |
+1 Ir per item |

Text size changes by +15 B on GIL and +552 B on FT, where GCC re-spends
the freed budget on `md_walk_with_hash()` and `_md_contains_locked()`.
The pure Python backend has no counterpart to these helpers.

## Are there changes in behavior for the user?

No.

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

No, it adds one attribute to each of nine existing helpers.

## Related issue number

Follow-up to #1667 and #1739.

## Checklist

... (continued)

793 of 1586 branches covered (50.0%)

Branch coverage included in aggregate %.

9326 of 10194 relevant lines covered (91.49%)

1.83 hits per line