RFR: 8330802: Desugar switch in Locale::createLocale

[Chen Liang]

On Mon, 22 Apr 2024 10:34:29 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> This switch expression in `Locale::createLocale` is causing a somewhat large startup regression on my local system. Desugaring to if statements seem like the right thing to do while we investigate ways to further reduce overheads in `SwitchBootstraps`.
> 
> These numbers are against a baseline which include #18865 and #18845, which already improved the situation:
> 
> 
> Name             Cnt          Base         Error           Test         Error         Unit  Change
> Perfstartup-Noop  20        40,500 ±       1,942         31,000 ±       2,673        ms/op   1,31x (p = 0,000*)
>   :.cycles           143254849,000 ± 3398321,355  102205427,650 ± 2192784,853       cycles   0,71x (p = 0,000*)
>   :.instructions     307138448,850 ± 2095834,550  219415574,800 ±  376992,067 instructions   0,71x (p = 0,000*)
>   :.taskclock               39,500 ±       1,942         22,500 ±       3,858           ms   0,57x (p = 0,000*)
>   * = significant
> 
> 
> Comparing to a baseline without those recent improvements the overhead was almost the double: 
> 
> Name             Cnt          Base         Error           Test         Error         Unit  Change
> Perfstartup-Noop  20        50,000 ±       0,000         31,000 ±       2,673        ms/op   1,61x (p = 0,000*)
>   :.cycles           187047932,000 ± 3330400,381  102205427,650 ± 2192784,853       cycles   0,55x (p = 0,000*)
>   :.instructions     408219060,350 ± 4031173,140  219415574,800 ±  376992,067 instructions   0,54x (p = 0,000*)
>   :.taskclock               53,500 ±       4,249         22,500 ±       3,858           ms   0,42x (p = 0,000*)
>   * = significant

src/java.base/share/classes/java/util/Locale.java line 1003:

> 1001:             return new Locale(lk.base, lk.exts);
> 1002:         } else {
> 1003:             throw new InternalError("should not happen");

The default branch was required in the switch. Can we simply drop this branch and have a ClassCastException to LocalKey instead?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18882#discussion_r1574727393