if (!VM.VerifyAssertions) VM._assert(false);
  public static final void linkedListInsert(VM_Address block, VM_Address prev) {    if (!VM.VerifyAssertions) VM._assert(false); // must be fixed    if (VM.VerifyAssertions) VM._assert(!block.isZero());    VM_Address next;    if (!prev.isZero()) {      next = VM_Magic.getMemoryAddress(prev.add(NEXT_FIELD_OFFSET));      VM_Magic.setMemoryAddress(prev.add(NEXT_FIELD_OFFSET), block);    } else      next = VM_Address.zero();    VM_Magic.setMemoryAddress(block.add(PREV_FIELD_OFFSET), prev);    VM_Magic.setMemoryAddress(block.add(NEXT_FIELD_OFFSET), next);    if (!next.isZero())      VM_Magic.setMemoryAddress(next.add(PREV_FIELD_OFFSET), block);  }