@Override
  public RegisterSpecList getSources() {
    if (sources != null) {
      return sources;
    }

    if (operands.size() == 0) {
      // How'd this happen? A phi insn with no operand?
      return RegisterSpecList.EMPTY;
    }

    int szSources = operands.size();
    sources = new RegisterSpecList(szSources);

    for (int i = 0; i < szSources; i++) {
      Operand o = operands.get(i);

      sources.set(i, o.regSpec);
    }

    sources.setImmutable();
    return sources;
  }
Gets sources. Constructed lazily from phi operand data structures and then cached.

@return {@code non-null;} sources list
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/PhiInsn.java