RFR: 8271459: C2: Missing NegativeArraySizeException when creating StringBuilder with negative capacity [v2]

[Tobias Hartmann]

On Mon, 27 Sep 2021 07:37:34 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> Stringopts does not take into account that a negative `int` argument for `StringBuilder(int)` results in a `NegativeArraySizeException` when optimizing away `StringBuilder` usages into single strings.
>> 
>> The suggested fix does the following:
>> - Bailout of Stringopts if C2 knows that an `int` argument is always negative.
>> - Apply stringopts but insert an additional runtime check with an UCT if C2 cannot tell if an `int` argument is positive or negative.
>> 
>> I added some IR tests to verify the fix and also ran some standard benchmarks.
>> 
>> I also updated `TestIRMatching` to test the new and updated default regexes.
>> 
>> Thanks,
>> Christian
>
> Christian Hagedorn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update UCT to Action_maybe_recompile

That looks good to me given that we check for `too_many_traps` in `StringConcat::validate_control_flow()`.

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Marked as reviewed by thartmann (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5652