RFR: 8258961: devirtualize SafePointNode::jvms() and hide out set_jvms()

[Vladimir Kozlov]

On Mon, 28 Dec 2020 09:48:29 GMT, Xin Liu <xliu at openjdk.org> wrote:

> SafePointNode::jvms() declares virtual but has never been overridden. It seems unnecessary.
> The member variable _jvms declares 'JVMState* const', but set_jvms() updates its value anyway.
> Geting rid of the const qualifier and hides if out using protected.

Also update last copyright year in changed files.

src/hotspot/share/runtime/vmStructs.cpp line 945:

> 943:                                                                                                                                      \
> 944:   c2_nonstatic_field(SafePointNode,            _jvms,                                         JVMState* const)                       \
> 945:                                                                                                                                      \

Don't remove it. It is referenced from HotSpot Servicability agent:
https://github.com/openjdk/jdk/blob/master/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/opto/SafePointNode.java#L45

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Changes requested by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1899