private void registerFieldUsage(int opcode, String owner, String fName, String desc) {
        if (opcode == Opcodes.PUTFIELD || opcode == Opcodes.PUTSTATIC) {
          addUsage(new FieldAssignUsage(owner, fName, desc));
        }
        if (opcode == Opcodes.GETFIELD || opcode == Opcodes.GETSTATIC) {
          Iterators.collect(TypeRepr.getType(desc).getUsages(), myUsages);
        }
        addUsage(new FieldUsage(owner, fName, desc));
      }
private void registerFieldUsage(int opcode, String owner, String fName, String desc)