RegAllocGreedy: Check if copied lanes are live in trySplitAroundHintReg#160424

arsenm merged 2 commits intomainllvm/llvm-project:mainfrom

users/arsenm/greedy/trySplitAroundHintReg-subregllvm/llvm-project:users/arsenm/greedy/trySplitAroundHintReg-subregCopy head branch name to clipboard