RFR: 8375038: C2: Enforce that Ideal() returns the root of the subgraph if any change was made by checking the node hash [v5]

[Benoît Maillard]

On Tue, 10 Feb 2026 08:26:07 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

>> Benoît Maillard has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Changed copyright on wrong file - hpp instead of cpp
>>  - Update copyright year
>
> src/hotspot/share/opto/intrinsicnode.cpp line 50:
> 
>> 48:   if (can_reshape) {
>> 49:     Node* mem = in(MemNode::Memory);
>> 50:     // If mem input is a MergeMem, get the desired slice
> 
> It might be obvious, but... I don't understand why it was wrong.

If `transform` makes changes to the memory input, but the resulting node is not a `MergeMem`, then we will return `nullptr` here. The hash will still be different (as the input has changed), thus triggering the assert.

And in any case `transform` should not be called here, we will be notified anyway if an input changes.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29421#discussion_r2786623486