RFR: 8353345: C2 asserts because maskShiftAmount modifies node without deleting the hash

[Marc Chevalier]

On Tue, 1 Apr 2025 11:51:13 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

> First delete the hash, then `set_req`. This way, we avoid changing the node (a non-`this` node) without deleting the hash. This wrong ordering is not new from [JDK-8347459](https://bugs.openjdk.org/browse/JDK-8347459), but before that, only `this` was going through this function, so it was ok. But since, it is used with other nodes, hence the need to remove the hash.
> 
> Also, not do any of that outside IGVN, but requires to register nested shifts for IGVN in parsing not to miss them later.
> 
> Thanks,
> Marc

That makes sense. I've done as described. Tests seem happy.

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PR Comment: https://git.openjdk.org/jdk/pull/24355#issuecomment-2773229850