RFR: 8328528: C2 should optimize long-typed parallel iv in an int counted loop

[Roland Westrelin]

On Tue, 26 Mar 2024 14:43:42 GMT, Kangcheng Xu <kxu at openjdk.org> wrote:

> Currently, parallel iv optimization only happens in an int counted loop with int-typed parallel iv's. This PR adds support for long-typed iv to be optimized. 
> 
> Additionally, this ticket contributes to the resolution of [JDK-8275913](https://bugs.openjdk.org/browse/JDK-8275913). Meanwhile, I'm working on adding support for parallel IV replacement for long counted loops which will depend on this PR.

That looks good to me. A comment that shows what the transformation does with pseudo code before and pseudo code after (before/after subgraphs) would be helpful I think.

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PR Review: https://git.openjdk.org/jdk/pull/18489#pullrequestreview-1983245569