private SsaBasicBlock eval(SsaBasicBlock v) {
    DFSInfo bbInfo = info[v.getIndex()];

    if (bbInfo.ancestor == null) {
      return v;
    }

    compress(v);
    return bbInfo.rep;
  }
Performs path compress on the DFS info.

@param in Basic block whose DFS info we are path compressing.
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/Dominators.java