RFR: 8347901: C2 should remove unused leaf / pure runtime calls [v2]

[Marc Chevalier]

On Mon, 23 Jun 2025 09:20:13 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> In an earlier issue ([JDK-8349523](https://bugs.openjdk.org/browse/JDK-8349523)), I tried to remove these nodes during parsing. It didn't work well. The problem is that it's transformed by GVN before setting any output projection, so of course, the node is removing itself before having the opportunity of being used. We wait until usages have been set before we try to remove the node (or replace it with a tuple).
>
> That sounds like a bug at the use-site... don't you think?

As discussed offline, it's relatively normal. Adding a comment to explain.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25760#discussion_r2161524761