RFR: 8281553: Ensure we only require liveness from mach-nodes with barriers [v2]

[Christian Hagedorn]

On Thu, 10 Feb 2022 09:01:43 GMT, Emanuel Peter <duke at openjdk.java.net> wrote:

>> Adding NULL check. This also ensures we are not returning a NULL reference.
>> 
>> Ran tests to ensure assert is never triggered.
>
> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fixing whitespaces

Looks good!

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Marked as reviewed by chagedorn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/7407