RFR: 8361842: Validate input in both Java and C++ for java.lang.StringCoding intrinsics

[Volkan Yazici]

On Fri, 27 Jun 2025 13:24:52 GMT, Chen Liang <liach at openjdk.org> wrote:

>> But the original code already checks for `len >= 0`, right? See `LibraryCallKit::inline_countPositives` -> `generate_string_range_check` -> `// Offset and count must not be negative`
>> 
>> This PR is about moving the range checks from the intrinsics into the Java wrappers. Removing range checks is out of the scope and should be carefully evaluated on a case-by-case basis separately.
>
> My point is this is a performance-sensitive API. We are using a known-slow check method `checkFromIndexSize` which may introduce a performance regression.

@liach, thanks for sharing your feedback on this draft, much appreciated. 🙇 In order to address your (rightful) concerns (which I also share) regarding the performance impact, in 196fc5d, I've added `StringCodingCountPositives` JMH benchmark and produced the following results:

*OS:* Ubuntu 24.04.2
*CPU:* Intel Core Ultra 9 185H x 22


Mode  Cnt  Score   Error  Units
avgt   10  8.617 ± 0.646  ns/op          # 149882416a9 (strIntrinCheck)
avgt   10  8.787 ± 0.313  ns/op          # 5a1301df195 (master)


AFAICT, (even though the patched version appears to be performing better 😛) the scores do match. Note that I will run the entire `test/micro/org/openjdk/bench/java/lang/String*.java` suite on various platforms and make sure there are no (visible?) performance regressions, before promoting this draft to a PR.

Let me know if this addresses your concerns and if there is anything else I can do to better assess the performance impact.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25998#discussion_r2185582087