RFR: 8276162: Optimise unsigned comparison pattern [v3]

[Vladimir Kozlov]

On Thu, 11 Nov 2021 05:12:09 GMT, Mai Đặng Quân Anh <duke at openjdk.java.net> wrote:

>> This patch changes operations in the form `x +- Integer.MIN_VALUE <=> y +- Integer.MIN_VALUE`, which is a pattern used to do unsigned comparisons, into `x u<=> y`.
>> 
>> In addition to being basic operations, they may be utilised to implement range checks such as the methods in `jdk.internal.util.Preconditions`, or in places where the compiler cannot deduce the non-negativeness of the bound as in `java.util.ArrayList`.
>> 
>> Thank you very much.
>
> Mai Đặng Quân Anh has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - replace cmpx->Opcode() with cmpx_op
>  - address reviews, remove checks for subtraction operatios

Thank you for addressing my comments.

I am tentatively approve these changes leaving final approval and testing to @TobiHartmann

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6101