RFR: JDK-8262994: Refactor String.split to help method inlining [v2]

[Naoto Sato]

On Mon, 9 Jan 2023 20:04:34 GMT, Christian Wimmer <cwimmer at openjdk.org> wrote:

>> The method `String.split` contains a fast-path when the regular expression parameter is not really a regular expression, but just a single split character.
>> This fast path vs. slow path check can be constant folded when the regular expression parameter is a literal constant - a quite frequent pattern (for example, all JDK usages of `String.split` have a constant expression parameter). But method inlining in JIT and AOT compilers can usually not inline `String.split` because the method body is too large. Factoring out the actual fast-path splitting logic into a separate method solves this problem: the JIT or AOT compiler can inline `String.split`, constant-fold the fast/slow path check, and then only the invoke of either the fast path or the slow path remains.
>
> Christian Wimmer has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add comment about method inlining

Looks good.

src/java.base/share/classes/java/lang/String.java line 3130:

> 3128:               ((ch-'A')|('Z'-ch)) < 0)) &&
> 3129:             (ch < Character.MIN_HIGH_SURROGATE ||
> 3130:              ch > Character.MAX_LOW_SURROGATE))

Not your change, but I'd replace them with `MIN_SURROGATE` and `MAX_SURROGATE` respectively, for readability, taking the opportunity.

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PR: https://git.openjdk.org/jdk/pull/11791