RFR: 8291302: ARM32: nmethod entry barriers support [v2]

[Martin Doerr]

On Mon, 5 Dec 2022 14:19:55 GMT, Aleksei Voitylov <avoitylov at openjdk.org> wrote:

>> This PR implements nmethod entry barriers for ARM32. It has already been implemented for other ports and is related with JDK-8290025 "Remove the Sweeper".
>
> Aleksei Voitylov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   save float registers

Please note that the memory barrier has caused a performance regression on PPC64 (as on AArch64): https://bugs.openjdk.org/browse/JDK-8295069
I'd probably assert `nmethod_patching_type() == NMethodPatchingType::stw_instruction_and_data_patch` instead of emitting a memory barrier because `LoadLoad` may or may not be strong enough depending on usage (e.g. generational ZGC uses instruction patching as well).

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PR: https://git.openjdk.org/jdk/pull/11442