RFR: 8252583: Clean up unused phi-to-copy degradation mechanism [v2]

Tue Sep 22 13:41:22 UTC 2020

On Tue, 22 Sep 2020 13:24:35 GMT, Roberto Castañeda Lozano <github.com+8792647+robcasloz at openjdk.org> wrote:

>> Thanks Tobias and Xin for the reviews! I updated the PR for the record, even if we might end up moving the assertions
>> somewhere else as per Vladimir's suggestion.
>
> 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().

Tested successfully on hs-tier1, hs-tier2, and hs-tier3.

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