8385939: [11u] Remove arm64 port

[gnu-andrew]

JDK-8168503 introduced an additional AArch64 port as part of the arm port opened up by Oracle in OpenJDK 9. This was later removed in JDK-8209093 as part of OpenJDK 12.

This leaves this unmaintained port in one LTS release, 11. The code does not build and, as far as I can see, has never been able to build as it contains references to FloatRegisterSet which has been defined in assembler_arm_32.hpp since import.

The prospect of removing it from 11u was raised when backporting the security issue, JDK-8364465. The presence of the arm64 port made it harder to apply the backported changes to the arm32 port and it was not possible to ascertain the need for changes in the arm64 port due to a lack of expertise with the port and the code not even building.

Leaving the unused code in the repository would be less of an issue if it was separated from the arm32 code. However, the presence of the port makes the arm32 port a mess of ifdefs and so in turn makes that harder to maintain, and prone to problems such as backporting patches actually being applied to similar aarch64 code without realisation.

Of course, this also makes it tricker to remove, but we do already have the patch from 12, and can perform additional verification with the C preprocessor. The fact that the removal patch applies cleanly to the arm64 only files shows how little has been touched since inclusion.

I'm creating this as a new bug as the removal, for some reason, is a JEP. I presume this was because of the work involved in testing the removal, but it is hardly an enhancement. I also believe the risk of removal is low, and will pay off over time.

Keeping this in draft while I verify changes further and we should also add JDK-8213204

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Issue

• JDK-8385939: [11u] Remove arm64 port (Bug - P4)

Reviewing

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$ git checkout pull/3189

Update a local copy of the PR:
$ git checkout pull/3189
$ git pull https://git.openjdk.org/jdk11u-dev.git pull/3189/head

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$ git pr checkout 3189

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https://git.openjdk.org/jdk11u-dev/pull/3189.diff

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[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @gnu-andrew This backport pull request is too large to be automatically evaluated as clean.