this.justAfterNull = checkNotNull(justAfterNull);
    }

    @Override
    public int compare(@Nullable String lhs, @Nullable String rhs) {
      if (lhs == rhs) {
        return 0;
      }
      if (lhs == null) {
        // lhs (null) comes just before justAfterNull.
        // If rhs is b, lhs comes first.
        if (rhs.equals(justAfterNull)) {
          return -1;
        }

      this.justAfterNull = checkNotNull(justAfterNull);
    }

    @Override
    public int compare(@Nullable String lhs, @Nullable String rhs) {
      if (lhs == rhs) {
        return 0;
      }
      if (lhs == null) {
        // lhs (null) comes just before justAfterNull.
        // If rhs is b, lhs comes first.
        if (rhs.equals(justAfterNull)) {
          return -1;
        }

				p.errorf("expected simple register reference")
			}
			a.Type = obj.TYPE_REG
			a.Reg = r1
			if r2 != 0 {
				// Form is R1:R2. It is on RHS and the second register
				// needs to go into the LHS.
				panic("cannot happen (Addr.Reg2)")
			}
		}
		// fmt.Printf("REG %s\n", obj.Dconv(&emptyProg, 0, a))
		p.expectOperandEnd()
		return
	}

	// Constant.
	haveConstant := false

<p>
Type inference solves type equations through <i>type unification</i>.
Type unification recursively compares the LHS and RHS types of an
equation, where either or both types may be or contain bound type parameters,
and looks for type arguments for those type parameters such that the LHS
and RHS match (become identical or assignment-compatible, depending on
context).