mut base.ControlFlowBreak

mut .match[R$0:imm,mut,read](m: mut base.ControlFlowMatch[imm base.Void,R$0]): R$0 -> …,
mut .match[R$0:imm,mut,read](m: mut base.ControlFlowMatch[imm base.Void,R$0]): R$0 -> …,