RFR: 8257498: Remove useless skeleton predicates [v3]

[Roland Westrelin]

On Wed, 20 Jan 2021 12:30:12 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> This enhancement removes useless skeleton predicates in the same way as we already remove normal useless predicates in `PhaseIdealLoop::eliminate_useless_predicates()`.
>> 
>> Thanks,
>> Christian
>
> Christian Hagedorn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix removal from global list and update get_skeleton_predicates

Other than that, looks good to me.

src/hotspot/share/opto/loopnode.cpp line 3585:

> 3583:   }
> 3584: }
> 3585: 

I didn't realize you would have to go through an extra list. So I guess what you had before with the get_opaque parameter was better.

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Marked as reviewed by roland (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2075