RFR: 8292082: Deprecate UseRTM* for removal

[Roman Kennke]

On Tue, 9 Aug 2022 15:59:21 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> HotSpot supports RTM (restricted transactional memory) to be used for locking and deoptimization. RTM has since been disabled in Intel processors due to security vulnerabilities [0] and IBM removed support for it since its Power 10 line. RTM adds unnecessarily to complexity and maintenance burden.
> 
> I would like to propose to deprecate the relevant flags for removal, and actually remove the flags and all related code in a later release, unless somebody comes up with a good reason and performance comparison to show that it's worth keeping.
> 
> [0] https://en.wikipedia.org/wiki/Transactional_Synchronization_Extensions#History_and_bugs
> 
> Testing:
>  - [x] runtime/CommandLine/VMDeprecatedOptions.java
>  - [x] tier1

Is there interest in getting rid of RTM locking, or should I close this PR as won't-fix at this point?

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PR: https://git.openjdk.org/jdk/pull/9810