private int getParamBase() {
    return regSize - desc.getParameterTypes().getWordCount() - (isStatic ? 0 : 1);
  }
Gets the register that begins the method's parameter range (including the 'this' parameter for
non-static methods). The range continues until {@code regSize}

@return register as noted above.
android/android_framework/dex-maker/src/main/java/com/android/dx/dex/file/DebugInfoDecoder.java