switch v.Op {
	case ssa.OpLoadReg:
		n, _ := ssa.AutoVar(v.Args[0])
		return n, ssa.SymRead
	case ssa.OpStoreReg:
		n, _ := ssa.AutoVar(v)
		return n, ssa.SymWrite

	case ssa.OpArgIntReg:
		// This forces the spill slot for the register to be live at function entry.
		// one of the following holds for a function F with pointer-valued register arg X:
		//  0. No GC (so an uninitialized spill slot is okay)