RFR: 8371643: Remove ThreadLocalAllocBuffer::_reserve_for_allocation_prefetch [v3]

[Albert Mingkun Yang]

On Fri, 14 Nov 2025 19:22:39 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Trivial removing obsoleted code for unsupported arch.
>> 
>> Test: tier1
>
> Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Merge branch 'master' into remove-tlab-reserve
>  - review
>  - remove-tlab-reserve

`AllocatePrefetchStyle == 3` means "generate one prefetch instruction per cache line".

This patch removes the reserved alignment that was required for `AllocatePrefetchStyle == 3` on SPARC, but that does not imply that `AllocatePrefetchStyle == 3` itself should be removed. (Maybe a separate ticket if it's indeed deemed useless.)

> PhaseMacroExpand::prefetch_allocation still mentions "BIS instruction is used on SPARC as prefetch".

Will remove it in the next revision.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/28240#issuecomment-3538970541