[llvm] [TargetInstrInfo] Add isSelfCopyNoop target hook to safely delete noop self-copies. (PR #195900)

[Jay Foad via llvm-commits]

jayfoad wrote:

> AArch64 overrides to return true only for COPY and X-register copy-like instructions (ORRXrs). W-register copies (ORRWrs/ORRWrr) always zero the upper 32 bits of the corresponding X register in hardware, so they are not safe to delete.

Do W-register copies have an implicit def of the corresponding X register?

https://github.com/llvm/llvm-project/pull/195900