protected final int getCategoryForSsaReg(int reg) {
    SsaInsn definition = ssaMeth.getDefinitionForRegister(reg);

    if (definition == null) {
      // an undefined reg
      return 1;
    } else {
      return definition.getResult().getCategory();
    }
  }
Returns the category (width) of the definition site of the register. Returns {@code 1} for
undefined registers.

@param reg register
@return {@code 1..2}
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/back/RegisterAllocator.java