RFR: 8254269: simplify Node::disconnect_inputs [v2]

[Claes Redestad]

On Sat, 10 Oct 2020 15:15:05 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Xin Liu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8254269: simplify Node::disconnect_inputs
>>   
>>   Optimize it for the precedence loop. because there's no null between
>>   2 non-null precedences, disconnect_inputs can break at a null value.
>
> Nice cleanup! A few suggestions inline, but looks good as-is, too.

I think the changes in b8a7275 might be fine, but they are more subtle than the cleanup in the preceding version and
I'm not comfortable reviewing them. I think it needs a more thorough examination of if those optimizations always hold.
Could probably use some more asserts, a few tests and lift the documented assumption of the structure of the input to a
more visible place. My suggestion is to push this ahead with the straightforward cleanup you had in 4a9d803 and file a
follow-up RFE for the other optimization.

-------------

PR: https://git.openjdk.java.net/jdk/pull/589