On Fri, 23 Jan 2026 10:20:37 GMT, Tobias Hartmann <[email protected]> wrote:
> Since [JDK-8247299](https://bugs.openjdk.org/browse/JDK-8247299), value > objects no longer use `markWord::always_locked_pattern` (see description of > [JDK-8247298](https://bugs.openjdk.org/browse/JDK-8247298) for more details). > Therefore, the limitations around storing the hash code in the mark word that > are mentioned in [JDK-8244975](https://bugs.openjdk.org/browse/JDK-8244975) > no longer exist. Let's enable this optimization. > > Running `System.identityHashCode(obj)` in a loop and passing various > primitive boxes leads to a **17-18x speedup** on my machine. I'm also seeing > a **7% improvement** in the score of the SPECjvm2008 serial benchmark but we > are still a bit behind baseline without `--enable-preview`. More improvements > to come. > > It's worth noting that value objects will lose their buffer object when > stored in a flat container or sometimes when being scalarized > ([JDK-8372268](https://bugs.openjdk.org/browse/JDK-8372268) will improve > this). The hash then needs to be re-computed, which is expensive. > > I'm working on ways to further improve this, see > [JDK-8252185](https://bugs.openjdk.org/browse/JDK-8252185). > > Thanks, > Tobias Yes, it's expected and intended. That said, I agree that someone from runtime/GC should review this. ------------- PR Comment: https://git.openjdk.org/valhalla/pull/1954#issuecomment-3790122096
