[llvm] [DebugInfo][InstrRef] Copy instr-ref to replacement instrs in X86FixupSetCCPass (PR #159777)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Oooooooooo. I think this actually might be non-trivial: INSERT_SUBREG doesn't always correspond to an actual instruction that does computation, I think it can be elided? If that's the case, the better representation is salvaging it to the setcc instruction and encoding the subreg-field in the "substitution" table.

Key question being: will INSERT_SUBREG always translate to a non-copy instruction that we can put an instr-number on. If it doesn't we should take the other approach (salvaging).

https://github.com/llvm/llvm-project/pull/159777