public void setBackMode() {
    backMode = true;
    useList = null;
    definitionList = null;
  }
Sets "back-convert mode". Set during back-conversion when registers are about to be mapped into
a non-SSA namespace. When true, use and def lists are unavailable.
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/SsaMethod.java