[jdk11u-dev] RFR: Allow building with Clang 13 [v9]

[Christoph Langer]

On Fri, 19 Aug 2022 20:16:25 GMT, Salander <duke at openjdk.org> wrote:

>> This patch backports changes from JDK14 commit ae5615c6142a4dc0d9033462f4880d7b3c127e26. It does not rename the class to markWord as the original patch does, but instead converts markOop to a markWord equivalent in-place. This patch allows the JDK to be built with Clang 13, as it avoids undefined behavior.
>> 
>> See the following for more information:
>> 
>>     https://bugs.openjdk.java.net/browse/JDK-8229258
>>     https://bugs.gentoo.org/817995
>>     https://mail.openjdk.java.net/pipermail/hotspot-dev/2019-July/038704.html
>>     https://mail.openjdk.java.net/pipermail/hotspot-dev/2019-July/038712.html
>>     https://reviews.llvm.org/D99790#2678384
>> 
>> This is a re-do of @Serebit's PR that erroneously targeted the jdk11u repository ([link](https://github.com/openjdk/jdk11u/pull/23)), the only difference is that some errors in the backport were corrected in the `shenandoahForwarding.inline.hpp` file to fix some compilation errors when compiling with `shenandoahgc` enabled.
>
> Salander has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Fix github action
>  - Temporarily build linux with clang as well for testing

The more I look at this, I think we should strive for a clean & full backport of https://bugs.openjdk.java.net/browse/JDK-8229258 if this is required to enable clang13 compilation.

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PR: https://git.openjdk.org/jdk11u-dev/pull/1284