public int makeNewSsaReg() {
    int reg = registerCount++;
    spareRegisterBase = registerCount;
    onInsnsChanged();
    return reg;
  }
Makes a new SSA register. For use after renaming has completed.

@return {@code >=0;} new SSA register.
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/SsaMethod.java