andygrove opened a new pull request, #23588:
URL: https://github.com/apache/datafusion/pull/23588
> This PR was created by an LLM as a draft PR. I will mark it as ready for
review after human review.
## Which issue does this PR close?
N/A — autonomous exploratory PR.
## Rationale for this change
Stream uppercase char mapping directly into the string builder in the
non-ASCII case-conversion path, eliminating the per-row String heap allocation
and copy that str::to_uppercase incurred (lowercase left unchanged for
final-sigma correctness; Utf8View left unchanged to preserve byte-identical
layout).
## What changes are included in this PR?
Stream uppercase char mapping directly into the string builder in the
non-ASCII case-conversion path, eliminating the per-row String heap allocation
and copy that str::to_uppercase incurred (lowercase left unchanged for
final-sigma correctness; Utf8View left unchanged to preserve byte-identical
layout).
## Are these changes tested?
Correctness: unit tests + seeded differential fuzz (bit-identical Arrow
output vs `main`).
Benchmark (criterion):
- upper_unicode_utf8: 7.073% faster (base 325499ns -> cand 302477ns)
- upper_unicode_large_utf8: 6.065% faster (base 325116ns -> cand 305397ns)
Full criterion output:
```text
upper_unicode_utf8 time: [302.60 µs 303.42 µs 304.22 µs]
change: [−7.2166% −7.0726% −6.9250%] (p = 0.00 <
0.05)
Performance has improved.
Found 14 outliers among 100 measurements (14.00%)
14 (14.00%) high severe
upper_unicode_large_utf8
time: [305.90 µs 306.55 µs 307.12 µs]
change: [−6.2853% −6.0652% −5.8544%] (p = 0.00 <
0.05)
Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
1 (1.00%) high mild
```
## Are there any user-facing changes?
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