SharedPreferences fail to save data if setting APP_OPTIM := release

Question

the SharedPreferences is called through jni from c++ code.
When APP_OPTIM := debug, the preference is saved, but not for release.

What does APP_OPTIM := release do?

Answer 1

UPDATE: It turns out the in the jni code, the return is omitted, perhaps with APP_OPTIM := debug, the return is added and for release, the return is omitted.

int getPreference(string x)
{
    jniGetPreference(x);
}


int getPreference(string x)
{
    return jniGetPreference(x);
}