RFR: 8371558: C2: Missing optimization opportunity in AbsNode::Ideal [v2]

[Benoît Maillard]

On Wed, 12 Nov 2025 06:36:44 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> Benoît Maillard has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update test/hotspot/jtreg/compiler/c2/TestMissingOptAbsZeroMinusX.java
>>   
>>   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
>
> Looks good, thanks!

Thank you for the reviews! @chhagedorn @TobiHartmann @robcasloz
>  At some point, we will have to think about some kind of system to enforce notification of indirect users "by construction", or at least make it possible to somehow detect when such notification may be needed.

I agree, this seems quite difficult to sustain over time. But finding a good solution is probably quite hard, as there are different locations in the code where these notifications can happen (`add_users_of_use_to_worklist` is only one of them).

In the meantime at least we get the opportunity to add more tests (most work in these PRs goes into reproducing these missing optimizations reliably and reducing the tests to the maximum), and this will still be super useful if we ever change the notification mechanism.

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PR Comment: https://git.openjdk.org/jdk/pull/28237#issuecomment-3526698145