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

[Nils Eliasson]

On Thu, 23 Sep 2021 13:25:51 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

If we hit the uncommontrap - should we recompile without applying strconcat? Or is this code so uncommon that we don't want to add complexity for that case?

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