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

[Christian Hagedorn]

> 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

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5652/files
  - new: https://git.openjdk.java.net/jdk/pull/5652/files/ab8b6f8a..4e4f5222

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5652&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5652&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5652.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5652/head:pull/5652

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