RFR: 8342662: C2: Add new phase for backend-specific lowering [v6]

[Xiaohong Gong]

On Tue, 14 Jan 2025 11:03:42 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> src/hotspot/share/opto/phaseX.cpp line 2310:
>> 
>>> 2308: Node* PhaseLowering::lower_node(Node* n) {
>>> 2309:   // Apply shared lowering transforms
>>> 2310: 
>> 
>> Per my understanding, this is a backend specific lowering phase, is there any scenario that a platform in-dependent lowering is needed here? As we already have the common GVN phase for common node idealize, is there any difference for such shared transformations? Thanks!
>
> Lowering is not idealisation so I think having backend independent lowering is fine in case we need it.

Yeah, I understand it. But I think it could make this specific phase more complex.  This gives one more choice to do the arch independent IR transformation, but it's really a question what the best place should be.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21599#discussion_r1915850627