[lworld] RFR: 8367785: [lworld] Compiler adherence to new memory model rules for strict instance fields

[Christian Hagedorn]

On Fri, 3 Oct 2025 14:12:34 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> The new memory model rules for strict instance fields (see [JDK-8366372](https://bugs.openjdk.org/browse/JDK-8366372)) require a memory barrier at the beginning of `java.lang.Object::<init>`. The JITs will try to omit it if the receiver type is statically known (potentially via CHA + a dependency) and the class does not contain any strict fields.
> 
> Potentially, there's some more tricks that we can play. Most importantly, I think we can omit barriers for final fields at the end of the constructors if the field is also strict. I filed [JDK-8369166](https://bugs.openjdk.org/browse/JDK-8369166) for this.
> 
> I added a test that already caught [JDK-8369044](https://bugs.openjdk.org/browse/JDK-8369044) and will fail immediately without the JIT changes (on AArch64).
> 
> Thanks,
> Tobias

Looks good to me and nice test!

test/hotspot/jtreg/compiler/valhalla/inlinetypes/TestStrictFieldBarriers.java line 204:

> 202:                 if (res != 1) {
> 203:                     System.err.println("Incorrect field value observed!");
> 204:                     System.exit(1);

Is there any particular reason why you don't throw a `RuntimeException` here instead?

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

Marked as reviewed by chagedorn (Committer).

PR Review: https://git.openjdk.org/valhalla/pull/1656#pullrequestreview-3303271947
PR Review Comment: https://git.openjdk.org/valhalla/pull/1656#discussion_r2405254858