RFR: 8350567: NMT: update VMATree::register_mapping to copy the existing tag of the region [v2]

[Johan Sjölen]

On Thu, 27 Feb 2025 09:38:12 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> When committing a sub-region (SR) in the middle of a reserved region (RR), we need to decide on the MemTag. To find the correct tag, we had to find the RR base and take the tag and use it for SR.
>> With this PR, there will be no need to find the RR base and the tag of the previous region of SR can be copied to the SR.
>> 
>> Tests:
>> linux-x64-debug, gtest:NMT*, runtime/NMT
>
> Afshin Zafari has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - removed extra whitespace.
>  - unit test added.

test/hotspot/gtest/nmt/test_vmatree.cpp line 728:

> 726: }
> 727: 
> 728: TEST_VM_F(NMTVMATreeTest, CommitUseFlagInplace) {

Change this test to use `expect_equivalent_form`, see other usages to see what should look like. You can add multiple checks even, so that we get how the range changes over time.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23771#discussion_r1973498475