On Mon, 25 May 2026 21:58:09 GMT, Vladimir Ivanov <[email protected]> wrote:
>> On bytecode level booleans are represented as ints and HotSpot JVM >> normalizes boolean values on memory accesses. It unconditionally applies >> normalization on boolean stores, but trusts on-heap boolean locations to >> hold normalized values. Normalization is applied on loads for off-heap and >> mismatched unsafe accesses . >> >> There are 2 normalization procedures used: (1) cast int to byte and test it >> against zero; and (2) truncation to least-significant bit. Truncation is >> preferred (due to performance considerations), but JNI mandates testing >> against zero and, historically, `#1` was used for off-heap unsafe accesses >> as well. It complicated the implementation (leading to subtle bugs) and >> introduced divergence in behavior at runtime (depending on execution mode >> and JIT-compilation peculiarities). >> >> The fix uses truncation uniformly across all execution modes. It simplifies >> implementation and eliminates possible divergence in behavior between >> execution modes. Also, it drastically simplifies future Unsafe API >> refactorings. >> >> There's one scenario left when it's possible to observe non-normalized >> values: when mismatched access pollutes the Java heap with a bogus boolean >> value, but then the value is read with a well-typed boolean access. >> >> Testing: hs-tier1 - hs-tier6 >> >> - [x] I confirm that I make this contribution in accordance with the >> [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). > > Vladimir Ivanov has updated the pull request incrementally with three > additional commits since the last revision: > > - Merge remote-tracking branch 'origin/boolean_normalize' into > boolean_normalize > - update > - Truncate boolean values Thanks for the feedback, John. > Request: Could you post FTR the output from the jtreg test, both before the > other changes are applied, and after? I attached test output logs to the bug (`test_before.ctz.log`, `test_before.mixed.log`, and `test_after.lsb.log`). > The MODE=MIXED has tricky expectations; maybe document in the switch on mode > (expected computation). `Mode.MIXED` has the following comment: MIXED("(x & 1) + (byte != 0)"); // Truncate to LSB on stores, compare to zero on loads Is it what you are asking for? ------------- PR Comment: https://git.openjdk.org/jdk/pull/31249#issuecomment-4548280131
