RFR: 8375038: C2: Enforce that Ideal() returns the root of the subgraph if any change was made by checking the node hash [v3]

[Benoît Maillard]

On Fri, 6 Feb 2026 10:42:35 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

>> Benoît Maillard has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add new flag bit to TestVerifyIterativeGVN
>
> src/hotspot/share/opto/phaseX.cpp line 2130:
> 
>> 2128:   C->remove_modified_node(k);
>> 2129: #ifndef PRODUCT
>> 2130:   uint hash_before = is_verify_Ideal_return() ? k->hash() : 0;
> 
> Is this ternary really needed? Same under.

The point was just to avoid useless computations. My assumption is that `hash` can be slightly expensive in some cases, but I must admit I have not checked every implementation (there are many).

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PR Review Comment: https://git.openjdk.org/jdk/pull/29421#discussion_r2773553096