RFR: 8259609: C2: optimize long range checks in long counted loops [v6]

[Roland Westrelin]

On Mon, 20 Sep 2021 21:20:57 GMT, Radoslaw Smogura <github.com+7535718+rsmogura at openjdk.org> wrote:

> I wonder if this would be a good direction, and if I can help somehow?

Do I understand right that you're suggesting modifying c2 so it handles long range checks with the existing range check optimizations (rc_predicate etc.)? The approach this PR has taken is to convert long range checks into int range checks so existing range check optimizations work as is. Ignoring the merit of either approach, what you're suggesting, if I understand right, is different so it can't help this particular PR.
If you get what you're suggesting working then I expect you'll hit the same roadblock that this PR hits: someone will have to validate the logic before it integrates. FWIW, John and I both spent quite a bit on time on this. John has validated most of the logic and I updated the PR according to his latest comments. It's unfortunate it's taking that much time, but I doubt going a different road makes a lot of sense at this point.

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PR: https://git.openjdk.java.net/jdk/pull/2045