RFR: 8334342: Add MergeStore JMH benchmarks [v4]

[Emanuel Peter]

On Mon, 17 Jun 2024 08:07:40 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> test/micro/org/openjdk/bench/java/lang/MergeStoreBench.java line 656:
>> 
>>> 654:         array[offset + 2] = (byte) (value >>  8);
>>> 655:         array[offset + 3] = (byte) (value      );
>>> 656:     }
>> 
>> You say that here `MergeStore` does not work. That is because the indices are increasing, but the shifts decreasing. So that does not work on little-endian machines (most architectures), but I would expect it to work on big-endian machines with https://github.com/openjdk/jdk/pull/19218.
>
> Big endian is often used in network data transmission scenarios, and it is common to process big endian data on a little endian machine. In this case, can it be optimized to Integer.reverseBytes & putIntLittleEndian on a LittleEndian machine? `setIntB -> setIntRL`

I had already suggested that here:
https://github.com/openjdk/jdk/pull/19218#pullrequestreview-2076196539
Feel free to file an RFE. Maybe someone wants to work on it. I think it would not be that hard to make it work given all the code that is already there now. And it would be helpful in for both big/little endian to be able to do both orders.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19734#discussion_r1643088147