RFR: 8263577: C2: reachable nodes shouldn't have dead uses at the end of optimizations [v2]

[Vladimir Ivanov]

On Mon, 15 Mar 2021 14:01:27 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> It's not uncommon for c2 to leave dead uses hanging from reachable
>> nodes. It's usually harmless but can cause confusion (such as in
>> valhalla JDK-8262289, not reproducible with non valhalla code AFAICT).
>> 
>> Most of the time, these are caused by calls to set_req() during igvn
>> that should be set_req_X() calls. I added a verification pass at the
>> end of optimization and fixed all the ones I found.
>
> Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   vladimir's review

Marked as reviewed by vlivanov (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/3012