RFR: 8270083: -Wnonnull errors happen with GCC 11.1.1

[Dean Long]

On Fri, 9 Jul 2021 00:28:38 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> I attempted to build OpenJDK on Fedora 34 with gcc-11.1.1-3.fc34.x86_64, but I saw following errors:
>> 
>> 
>> In file included from /home/ysuenaga/github-forked/jdk/src/hotspot/share/runtime/frame.inline.hpp:42,
>>                  from /home/ysuenaga/github-forked/jdk/src/hotspot/cpu/x86/abstractInterpreter_x86.cpp:29:
>
> It is better if we can treat registers as a class **normally**. Similar change happens for markWord in [JDK-8229258](https://bugs.openjdk.java.net/browse/JDK-8229258). Should we change like now?

@YaSuenag I'm in favor of a permanent solution, assuming there's no regression in footprint or code quality.  See https://bugs.openjdk.java.net/browse/JDK-8269122 for a related improvement.

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PR: https://git.openjdk.java.net/jdk/pull/4719