[llvm] [RISCV][MCP] Remove redundant move from tail duplication (PR #89865)

[Piyou Chen via llvm-commits]

BeMg wrote:

> Removing `CopyOperands.Source->isRenamable()` from `isBackwardPropagatableCopy` is another way to fix this without changing `copyPhysReg`. `propagateDefs` checks the renamable flag on the def it is propagating into. So the check in `isBackwardPropagatableCopy` might not be functionally needed.

How about inherit the `isRenamable` during the `TargetInstrInfo::lowerCopy`?

https://github.com/llvm/llvm-project/pull/89865