RFR: 8367967: C2: "fatal error: Not monotonic" with Mod nodes

Mon Sep 22 07:09:14 UTC 2025

On Mon, 22 Sep 2025 06:49:49 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> Btw. why do we get always zero size replay files when running into the issue ?
> 
> ```
> # Internal Error (/priv/jenkins/client-home/workspace/openjdk-jdk-dev-linux_aarch64-dbg/jdk/src/hotspot/share/opto/phaseX.cpp:2763), pid=1089937, tid=1089972
> # fatal error: Not monotonic
> ```
> 
> Is it another bug of the replay file generation or a known limitation ?

We've encountered empty replay files before which could be traced back to a timeout in error reporting due to threads being stuck. We filed [JDK-8297588](https://bugs.openjdk.org/browse/JDK-8297588) for it but it's not fixed, yet. I did a closer investigation back there (see [summary](https://bugs.openjdk.org/browse/JDK-8297588?focusedId=14543145&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14543145)). You might be hitting the same issue.

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PR Comment: https://git.openjdk.org/jdk/pull/27408#issuecomment-3317270620