RFR: 8283094: Add Ideal transformation: x + (con - y) -> (x - y) + con [v5]

[Zhiqiang Zang]

On Tue, 29 Mar 2022 21:57:01 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> But in this case it seems OK to me to make the transformation, for example:
>> 
>> for (int i = 0; i < 10000; i++) {
>>     a[x + (MAX - i)] = b[x + (MAX - i)]; // a[(x - i) + MAX] = b[(x - i) + MAX]
>> }
>> 
>> Is there something I overlooked?
>
> In loopopts (and superword) we are loking for `(+-phi  +- const)` pattern for loop variable.
> With your transformation we get `((+-phi +- x) + const)` which may prevent some optimizations.

Makes sense. Thanks for the explanation. I included the check in a new commit.

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PR: https://git.openjdk.java.net/jdk/pull/7795