// For live instructions that have all dead bits, first make them dead by
// replacing all uses with something else. Then, if they don't need to
// remain live (because they have side effects, etc.) we can remove them.
// For live instructions that have all dead bits, first make them dead by
// replacing all uses with something else. Then, if they don't need to
// remain live (because they have side effects, etc.) we can remove them.