8372641: [s390x] Test failure TestMergeStores.java

[Harshit470250]

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.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8372641: [s390x] Test failure TestMergeStores.java (Bug - P4)

Reviewers

• Manuel Hässig (@mhaessig - Committer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/28523/head:pull/28523
$ git checkout pull/28523

Update a local copy of the PR:
$ git checkout pull/28523
$ git pull https://git.openjdk.org/jdk.git pull/28523/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 28523

View PR using the GUI difftool:
$ git pr show -t 28523

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/28523.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back Harshit470250! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@Harshit470250 The following label will be automatically applied to this pull request:

• hotspot-compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[mlbridge]

Webrevs

• 02: Full - Incremental (d5ad5e4a)
• 01: Full - Incremental (61352bdc)
• 00: Full (36c6de13)

[mhaessig]

Thank you for fixing this, @Harshit470250. The new instructions look good to me. I am only unsure about the cost (see comments below).

[mhaessig]

Thanks for addressing my comments. This looks good to me.