RFR: 8281732: add assert for non-NULL assumption for return of unique_ctrl_out [v4]

[Christian Hagedorn]

On Wed, 16 Feb 2022 08:01:49 GMT, Emanuel Peter <duke at openjdk.java.net> wrote:

>> unique_ctrl_out was used in contexts where NULL may be a valid return, and is also used in contexts where NULL is not expected.
>> 
>> I improved the code by having two functions instead:
>> unique_ctrl_out_or_null: return the unique control out, or NULL if there is no or more than one control out.
>> unique_ctrl_out: return the unique control out, assert if there is no or more than one control out.
>> 
>> This makes implicit assumptions explicit and also validates them in the future.
>> 
>> I changed the usage to unique_ctrl_out_or_null where NULL is among the expected return values.
>> 
>> Ran tests to verify that the assert never triggers.
>
> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix indentation in src/hotspot/share/opto/node.cpp
>   
>   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>

Marked as reviewed by chagedorn (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/7462