8337593: Using actual RegisterMap instead of copy

[neethu-prasad]

[Not ready. Work in progress. Draft pull request to verify tests]
Notes:
On a sample application's profiler using VM_ThreadDump, 24.52% (of VM thread) CPU cycle was spent on copying RegisterMap. Pass by value seems to perform better.

jdk/src/hotspot/share/runtime/vframe.cpp

Line 97 in 5dc9723

RegisterMap temp_map = *register_map();

Testing

1. tier 1 / tier 2 tests passed.

Appreciate feedback incase there is impact to other VM operations.

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Progress

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Integration blocker

 ⚠️ Title mismatch between PR and JBS for issue JDK-8337593

Issue

• JDK-8337593: Investigate VM_ThreadDump performance (Enhancement - P4) ⚠️ Title mismatch between PR and JBS.

Reviewing

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Update a local copy of the PR:
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$ git pr checkout 23918

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https://git.openjdk.org/jdk/pull/23918.diff

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