RFR: 8294540: Remove Opaque2Node: it is broken and triggers assert [v2]

[Emanuel Peter]

On Sat, 3 Dec 2022 01:05:22 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> I agree with removal of `Opaque2`.
>> 
>> On side note, please file RFE to rename all `Opaque` nodes to something meaningful.
>> With removal of `Opaque2` numbering is broken. Originally it was only 2 such nodes but now we have 4 and it become hassle to find what they do and why we have so many.
>
>> On side note, please file RFE to rename all `Opaque` nodes to something meaningful. With removal of `Opaque2` numbering is broken. Originally it was only 2 such nodes but now we have 4 and it become hassle to find what they do and why we have so many.
> 
> That is a good idea. I've planned to rename `Opaque4` nodes and get rid of some of their usages in the redesign of the skeleton predicates ([JDK-8288981](https://bugs.openjdk.org/browse/JDK-8288981)). But it could already be done earlier together with renaming the other opaque nodes now that we get rid of `Opaque2` nodes.

Thanks @chhagedorn for the previous investigation into Opaque2, and the review! Thanks @vnkozlov for the review!
I created two RFE, one for re-investigation/re-implementation of Opaque2, and one for renaming of Opaque nodes in general.

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PR: https://git.openjdk.org/jdk/pull/11477