RFR: 8281429: PhiNode::Value() is too conservative for tripcount of CountedLoop [v6]

[Xin Liu]

On Thu, 14 Apr 2022 15:45:51 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> src/hotspot/share/opto/loopnode.cpp line 854:
>> 
>>> 852:     swap(lo, hi);
>>> 853:   }
>>> 854:   if (hi->hi_as_long() <= lo->lo_as_long()) {
>> 
>> why this is <= instead of < ?
>
> If hi->hi_as_long() == lo->lo_as_long() the body is entered at most once and there's no loop, right?
> FWIW, this test is in case the LongCountedLoop was created in the current pass of loop opts and igvn hasn't had a chance to run yet (and optimize the backedge out).

yes. 
I see. we don't need to generated nested loop for it.

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PR: https://git.openjdk.java.net/jdk/pull/7823