Currently, the hotspot compiler (as in ciField) trusts final fields in hidden classes, record classes, and selected jdk packages. Some classes in the JDK wish to be trusted, but they cannot apply package-wide opt-in due to other legacy classes in the package, such as java.util.
They currently can use `@Stable` as a workaround, but this is fragile because a stable final field may hold a trusted null, zero, or false value, which is currently treated as non-constant by ciField. We should add an annotation to opt-in for a whole class, mainly for legacy packages. This would benefit greatly some of our classes already using a lot of Stable, such as java.util.Optional, whose empty instance is now constant-foldable, as demonstrated in a new IR test. Paging @minborg who requested Optional folding for review. I think we can remove redundant Stable in a few other java.util classes after this patch is integrated. I plan to do that in subsequent patches. ------------- Commit messages: - Spurious change - Merge branch 'master' of https://github.com/openjdk/jdk into feature/class-final-trusting - Issue number and test update - Fixed optional and unit test - Merge branch 'master' of https://github.com/openjdk/jdk into feature/class-final-trusting - Stage Changes: https://git.openjdk.org/jdk/pull/28540/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28540&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8372696 Stats: 183 lines in 13 files changed: 169 ins; 13 del; 1 mod Patch: https://git.openjdk.org/jdk/pull/28540.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/28540/head:pull/28540 PR: https://git.openjdk.org/jdk/pull/28540
