Optimize unrecognized intrinsic candidates in jdk.misc.Internal.Unsafe

[jmesyou]

This epic tracks the ongoing work and status of lowering currently unrecognized @IntrinsicCandidate methods in the jdk.internal.misc.Unsafe class in the JIT compiler.

• storeStoreFence (Optimize jdk.internal.misc.Unsafe.storeStoreFence() into no-op on x86 platforms #19042)
• getAndAddByte
• getAndSetShort
• getAndSetShort
• getAndAddShort
• getShortUnaligned
• putShortUnaligned
• getIntUnaligned
• putIntUnaligned
• getLongUnaligned
• putLongUnaligned
• allocateUninitializedArray
• writeback0

[jmesyou]

The instruction for CLWB was implemented in eclipse-omr/omr#7253. The intention was to lower calls to writeback0 to the CLWB instruction in the x86 backend but support for writeback0 is unnecessary because OpenJ9 has taken a different approach. A native implementation of writebackMemory, the only parent caller of writeback0, is provided for the runtime instead of writeback0. Therefore calls to writeback0 are never made and never need to be recognized nor replaced by the JIT compiler.