RFR: 8267928: Loop predicate gets inexact loop limit before PhaseIdealLoop::rc_predicate

[Yi Yang]

On Tue, 1 Jun 2021 07:00:11 GMT, Nils Eliasson <neliasso at openjdk.org> wrote:

>> Loop predicate gets inexact loop limit(LoopLimitNode) from exact_limit(even if the limit is statically known) and does unnecessary overflow checking when generating lower bound test(rc_predicate). The reason is rather straightforward: exact_limit fails to see a HasExactTripCount flag since it would be set after performing loop predicate(iteration_split).
>
> Testing looks good.
> 
> Do you have any concrete example for when this happens?

@neliasso I've raised a concrete example about this, can you plz take a look once you have time. Thank you!

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PR: https://git.openjdk.java.net/jdk/pull/4247