[jdk8u-dev] RFR: 8186787: clang-4.0 SIGSEGV in Unsafe_PutByte [v2]

[Zdenek Zambersky]

> This backport fixes [failures](https://github.com/zzambers/jdk8u-dev/actions/runs/9858657012/job/27221579883) (segfaults) in following tests which appeared after [macos update](https://github.com/openjdk/jdk8u-dev/pull/544):
> 
> sun/misc/CopyMemory.java 
> compiler/unsafe/OpaqueAccesses.java
> 
> Backport differs from original changeset, because there were significant changes/refactoring in unsafe.
> 
> **Notes:**
> - [original changeset](https://github.com/openjdk/jdk11u-dev/commit/6dc1d8c06d98e127b022886172e16b90bf357c97) changes pointer returned by `addr` (`MemoryAccess` class), to volatile. Otherwise it is basically just refactoring.
> - `MemoryAccess` is used by `Unsafe_{Set,Put}*` and `Unsafe_{Set,Put}*Volatile` functions, defined using `DEFINE_GETSETOOP` and `DEFINE_GETSETOOP_VOLATILE` macros
> - jdk8 does not have `MemoryAccess` class, so equivalent pointers, in functions mentioned higher, are cast to volatile, to achieve same effect
> 
> Testing:
> Tier1: OK (fixes `sun/misc/CopyMemory.java` and `compiler/unsafe/OpaqueAccesses.java` tests on macos, 1 failure on Linux x86 is timeout - seems unrelated, macos failures explained here: https://github.com/openjdk/jdk8u-dev/pull/544#issuecomment-2250636257)

Zdenek Zambersky has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Add comment
 - Unsafe fix

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

Changes: https://git.openjdk.org/jdk8u-dev/pull/553/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=553&range=01
  Stats: 9 lines in 1 file changed: 7 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/553.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/553/head:pull/553

PR: https://git.openjdk.org/jdk8u-dev/pull/553