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

[Yi Yang]

On Fri, 28 May 2021 13:29:36 GMT, Yi Yang <yyang 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).

Unfortunately, I can not reproduce this with the aforementioned simple case when merged with master. I think some other patches affect generated IR. But the problem is still left behind, i.e. HasExactTripCount flag since it would be set after performing loop predicate. Should we move this PR forward?

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