RFR: 8372641: [s390x] Test failure TestMergeStores.java [v2]

[Amit Kumar]

On Thu, 27 Nov 2025 08:43:16 GMT, Harshit470250 <duke at openjdk.org> wrote:

>> [JDK-8347405](https://bugs.openjdk.org/browse/JDK-8347405) introduced a mergeStores optimisation which requires ReverseBytesS opcode and as it was not implemented for s390 the test case is failing.
>> I also implemented ReverseBytesUS.
>
> Harshit470250 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Apply suggestions from code review
>   
>   Review
>   
>   Co-authored-by: Manuel Hässig <manuel at haessig.org>
>   Co-authored-by: Amit Kumar <amitlocham09 at icloud.com>

Changes requested by amitkumar (Committer).

src/hotspot/cpu/s390/s390.ad line 11623:

> 11621: 
> 11622:   format %{ "LRVR   $dst, $src\n\t # byte reverse int"
> 11623:             "SRA    $dst, 0x0010\t # right shift by 16" %}

Suggestion:

            "SRA    $dst, 0x0010\t # right shift by 16, sign extended" %}

src/hotspot/cpu/s390/s390.ad line 11639:

> 11637: 
> 11638:   format %{ "LRVR   $dst, $src\n\t # byte reverse int"
> 11639:             "SRL    $dst, 0x0010\t # right shift by 16" %}

Suggestion:

            "SRL    $dst, 0x0010\t # right shift by 16, zero extended" %}

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

PR Review: https://git.openjdk.org/jdk/pull/28523#pullrequestreview-3514039618
PR Review Comment: https://git.openjdk.org/jdk/pull/28523#discussion_r2567602172
PR Review Comment: https://git.openjdk.org/jdk/pull/28523#discussion_r2567603002