RFR: 8329331: Intrinsify Unsafe::setMemory [v24]

[Vladimir Kozlov]

On Fri, 19 Apr 2024 22:08:52 GMT, Scott Gibbons <sgibbons at openjdk.org> wrote:

>> This code makes an intrinsic stub for `Unsafe::setMemory` for x86_64.  See [this PR](https://github.com/openjdk/jdk/pull/16760) for discussion around this change.
>> 
>> Overall, making this an intrinsic improves overall performance of `Unsafe::setMemory` by up to 4x for all buffer sizes.
>> 
>> Tested with tier-1 (and full CI).  I've added a table of the before and after numbers for the JMH I ran (`MemorySegmentZeroUnsafe`).
>> 
>> [setMemoryBM.txt](https://github.com/openjdk/jdk/files/14808974/setMemoryBM.txt)
>
> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Long to short jmp; other cleanup

`runtime/Unsafe/InternalErrorTest.java` test SIGBUS when run with `-Xcomp` (and other flags in test's @run command):

#  SIGBUS (0xa) at pc=0x0000000119514760, pid=63021, tid=28163
#
# JRE version: Java(TM) SE Runtime Environment (23.0) (fastdebug build 23-internal-2024-04-19-2326152.vladimir.kozlov.jdkgit2)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 23-internal-2024-04-19-2326152.vladimir.kozlov.jdkgit2, compiled mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, bsd-amd64)
# Problematic frame:
# v  ~StubRoutines::jbyte_fill 0x0000000119514760

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PR Comment: https://git.openjdk.org/jdk/pull/18555#issuecomment-2067547078