RFR: 8302872: Speed up StringLatin1.regionMatchesCI_UTF16

[Eirik Bjorsnos]

On Sat, 18 Feb 2023 18:22:49 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

> This PR continues the efforts from #12632 to speed up case-insensitive string matching.
> 
> We now tackle case-insensitive comparison of mixed-coder strings, implemented in `StringLatin1.regionMatchesCI_UTF16`
> 
> Key insights:
> 
> - If the UTF16 code point is also in latin1 range, we can leverage improvements from 12632 directly by calling `CharacterDataLatin1.equalsIgnoreCase`
> - There are exactly 7 non-latin1 Unicode code points which case fold into the latin1 range. We can special-case our comparison of these code points by adding the method `CharacterDataLatin1.latin1CaseFold`.
> - To avoid checking of `a == b` twice, this check is lifted out of `CharacterDataLatin1.equalsIgnoreCase` and the two callers are updated to check that `a != b` before calling the method. 
>  
> For completeness, the RegionMatches test is updated to also compare Turkic dotted/dotless 'i's against the uppercase ASCII 'I', not just the lowercase one.  Not stricktly related to the purpose of this PR, but it did help catch a regression introduced in an earlier iteration of the PR.   
> 
> To guard against regressions caused by future changes to the set of Unicode code points folding into latin1, a new test is added to `EqualsIgnoreCase` which identifies all such code points and verifies they are compared correcty.
> 
> Performance is tested for matching and mismatching cases of selected code point pairs picked from the ASCII letter, ASCII number, latin1 letter and non-latin Unicode letter ranges. Results in the first comment below.

Benchmark results:

Baseline:


Benchmark                                 (codePoints)  (size)  Mode  Cnt      Score     Error  Units
RegionMatchesIC.Mixed.regionMatchesIC      ascii-match    1024  avgt   15   1497.391 ±  22.350  ns/op
RegionMatchesIC.Mixed.regionMatchesIC   ascii-mismatch    1024  avgt   15      5.346 ±   0.165  ns/op
RegionMatchesIC.Mixed.regionMatchesIC     number-match    1024  avgt   15    364.034 ±   5.561  ns/op
RegionMatchesIC.Mixed.regionMatchesIC  number-mismatch    1024  avgt   15      4.036 ±   0.171  ns/op
RegionMatchesIC.Mixed.regionMatchesIC       lat1-match    1024  avgt   15   2674.043 ± 174.669  ns/op
RegionMatchesIC.Mixed.regionMatchesIC    lat1-mismatch    1024  avgt   15      6.493 ±   0.230  ns/op
RegionMatchesIC.Mixed.regionMatchesIC      utf16-match    1024  avgt   15  12630.314 ± 212.472  ns/op
RegionMatchesIC.Mixed.regionMatchesIC   utf16-mismatch    1024  avgt   15     14.796 ±   0.359  ns/op



PR:


Benchmark                                 (codePoints)  (size)  Mode  Cnt     Score    Error  Units
RegionMatchesIC.Mixed.regionMatchesIC      ascii-match    1024  avgt   15  1449.499 ± 14.350  ns/op
RegionMatchesIC.Mixed.regionMatchesIC   ascii-mismatch    1024  avgt   15     3.450 ±  0.082  ns/op
RegionMatchesIC.Mixed.regionMatchesIC     number-match    1024  avgt   15   362.582 ±  2.963  ns/op
RegionMatchesIC.Mixed.regionMatchesIC  number-mismatch    1024  avgt   15     3.259 ±  0.021  ns/op
RegionMatchesIC.Mixed.regionMatchesIC       lat1-match    1024  avgt   15  1625.513 ± 14.305  ns/op
RegionMatchesIC.Mixed.regionMatchesIC    lat1-mismatch    1024  avgt   15     3.858 ±  0.027  ns/op
RegionMatchesIC.Mixed.regionMatchesIC      utf16-match    1024  avgt   15  1422.722 ± 85.581  ns/op
RegionMatchesIC.Mixed.regionMatchesIC   utf16-mismatch    1024  avgt   15     3.756 ±  0.089  ns/op

-------------

PR: https://git.openjdk.org/jdk/pull/12637