RFR: 8261837: SIGSEGV in ciVirtualCallTypeData::translate_from [v2]

[Dean Long]

> Type profiling code based on the x86 implementation uses XOR to check if the MDO value matches the klass, then later stores that XORed value into the MDO if the MDO value was 0.  However, there is a race here if we reload the MDO value to check for 0, resulting in storing OBJ_KLASS XOR MDO_KLASS back to the MDO.
> 
> I took a stab at riscv, but I don't have a way to test it.

Dean Long has updated the pull request incrementally with one additional commit since the last revision:

  redo for x86

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16750/files
  - new: https://git.openjdk.org/jdk/pull/16750/files/ed8ea27b..d6f71bbd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16750&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16750&range=00-01

  Stats: 75 lines in 3 files changed: 41 ins; 7 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/16750.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16750/head:pull/16750

PR: https://git.openjdk.org/jdk/pull/16750