private boolean isSubroutineCaller(BasicBlock bb) {
    IntList successors = bb.getSuccessors();
    if (successors.size() < 2) return false;

    int subLabel = successors.get(1);

    return (subLabel < subroutines.length) && (subroutines[subLabel] != null);
  }
Checks to see if the basic block is a subroutine caller block.

@param bb {@code non-null;} the basic block in question
@return true if this block calls a subroutine
android/android_framework/dex-maker/src/main/java/com/android/dx/cf/code/Ropper.java