RFR: 8254887: C2: assert(cl->trip_count() > 0) failed: peeling a fully unrolled loop [v2]

[Tobias Hartmann]

On Thu, 12 Nov 2020 15:22:15 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> A loop's trip count is computed to have exact trip count 6. Then:
>> 
>> 1- pre/main/post loops are created which brings the trip count from 6
>>   to 5
>> 2- main loop is unrolled which brings the trip count to 2
>> 3- main loop is peeled: Trip count is 1
>> 4- pre/main/post loops are created again. Trip count of main loop is 0.
>> 5- peeling is attempted again and the assert fires
>> 
>> IdealLoopTree::policy_peeling() doesn't attempt peeling if the trip
>> count is 1. I propose that IdealLoopTree::policy_range_check() (that
>> causes the pre/main/post loops insertion the second time) performs the
>> same check so step 4 doesn't happen.
>
> Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - only for normal loops
>  - test
>  - fix

Marked as reviewed by thartmann (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/1096