Review

class ReferenceCollectingCallback.ReferenceCollection {
    /**
     * Determines if the variable for this reference collection is
     * "well-defined." A variable is well-defined if we can prove at
     * compile-time that it's assigned a value before it's used.
     *
     * Notice that if this function returns false, this doesn't imply that the
     * variable is used before it's assigned. It just means that we don't
     * have enough information to make a definitive judgement.
     */
    protected boolean isWellDefined() {
      int size = references.size();
      if (size == 0) {
        return false;
      }

      // If this is a declaration that does not instantiate the variable,
      // it's not well-defined.
      Reference init = getInitializingReference();
      if (init == null) {
        return false;
      }

      Preconditions.checkState(references.get(0).isDeclaration());
      BasicBlock initBlock = init.getBasicBlock();
      for (int i = 1; i < size; i++) {
        if (!initBlock.provablyExecutesBefore(
                references.get(i).getBasicBlock())) {
          return false;
        }
      }

      return true;
    }

}