On Mon, 6 Oct 2025 12:13:06 GMT, Christian Hagedorn <[email protected]> wrote:
> `test9()` in `TestLWorld.java` is crashing intermittently when running with > `StressLoopPeeling`. > > The problem can be traced back to a node that is not re-added to the IGVN > worklist in `PhiNode::Ideal()`: > <img width="282" height="198" alt="graph" > src="https://github.com/user-attachments/assets/e8597cf1-d49f-4c8d-b248-184b25f30fba"; > /> > > We are processing `3786 Phi` and update its input `3748 Phi` to another node. > As a result, `3748 Phi` loses it's last output and is now dead. It should be > re-added to the IGVN worklist to be cleaned up. But that does not happen > because we use `set_req()` on `3786 Phi` instead of `set_req_X()` when > replacing the input `3748 Phi`. As a result, the dead node stays in the graph > and eventually triggers the "no dead use" assert. > > The fix is straight forward to use `set_req_X()` which ensures that a now > dead input node is pushed to the IGVN worklist again and cleaned up later. > > The affected code is also wrong in mainline but has never triggered there. > Therefore, I suggest to wait and not eagerly upstream it to mainline for now. > > Thanks, > Christian This pull request has now been integrated. Changeset: 619825cd Author: Christian Hagedorn <[email protected]> URL: https://git.openjdk.org/valhalla/commit/619825cd7640af99253455dda68e8b9d9018d478 Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod 8368782: [lworld] C2: fatal error: no reachable node should have no use Reviewed-by: thartmann ------------- PR: https://git.openjdk.org/valhalla/pull/1662
