RFR: 8252583: Clean up unused phi-to-copy degradation mechanism [v4]

[Vladimir Kozlov]

On Tue, 22 Sep 2020 13:31:05 GMT, Roberto Castañeda Lozano <github.com+8792647+robcasloz at openjdk.org> wrote:

>> Remove unused notion of "PhiNode-to-copy degradation", where PhiNodes can be degraded to copies by setting their
>> RegionNode to NULL. Remove corresponding `PhiNode::is_copy()` test, which always returned NULL (false). Assert that
>> PhiNodes have an associated RegionNode in `PhiNode::Ideal()`.
>
> Roberto Castañeda Lozano has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Clean up unused PhiNode-to-copy degradation
>   
>   Remove unused notion of 'PhiNode-to-copy degradation', where PhiNodes can be
>   degraded to copies by setting their RegionNode to NULL. Remove corresponding
>   PhiNode::is_copy() test, which always returned NULL (false). Assert that
>   PhiNodes have an associated RegionNode in PhiNode::Ideal().

Good.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/275