RFR: 8345287: C2: live in computation is broken

Fri Dec 6 08:01:40 UTC 2024

On Thu, 5 Dec 2024 17:05:36 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> All benefits described in [JDK-8234003](https://bugs.openjdk.org/browse/JDK-8234003) could be due to not iterating at all in `add_liveout()`. Fixing it will place us at least at the same state as before those changes.
> 
> -5% regression in monte-carlo is seen only on old macos-x64 machine which does not have AVX512 (only AVX2). It would be interesting to investigate but I think it is fine if we do that after push. So I agree to integrate this fix into JDK 24. Fixing regression could be done in 24u update release.
> 
> `OptoRegScheduling` should be investigated separately (in JDK 25) regardless this fix.

OK.

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PR Comment: https://git.openjdk.org/jdk/pull/22473#issuecomment-2522428369