const bool need_save_spells
            = (!name.empty()
               && (!mons_class_flag(monster->type, M_SPELLCASTER)
                   || mons_class_flag(monster->type, M_ACTUAL_SPELLS)));

    // Keep spells for named monsters.
    if (!name.empty())

    // Keep spells for named monsters, but don't override innate ones
    // for dragons and the like. This means that Sigmund polymorphed
    // into a goblin will still cast spells, but if he ends up as a
    // swamp drake he'll breathe fumes and, if polymorphed further,
    // won't remember his spells anymore.
    if (need_save_spells
        && (!mons_class_flag(monster->type, M_SPELLCASTER)
            || mons_class_flag(monster->type, M_ACTUAL_SPELLS)))
    {

    }

}
static bool _mon_has_spells(monsters *monster)
{
    for (int i = 0; i < NUM_MONSTER_SPELL_SLOTS; ++i)
        if (monster->spells[i] != SPELL_NO_SPELL)
            return (true);
    return (false);

    // A polymorphed unique will retain his or her spells even in another
    // form. If the new form has the SPELLCASTER flag, casting happens as
    // normally, otherwise we need to enforce it, but it only happens with
    // a 50% chance.
    const bool spellcasting_poly
            = !mons_class_flag(monster->type, M_SPELLCASTER)
              && mons_class_flag(monster->type, M_SPEAKS)
              && _mon_has_spells(monster);

           && !spellcasting_poly

        && (priest || wizard

        && (priest || wizard || spellcasting_poly

    else if (spellcasting_poly && coinflip()) // 50% chance of not casting
        return (false);

You can try tweaking a number of options to see whether performance improves:
tile_title_screen = false
    For weak drivers, the title screen can take a long time to load. If this
    bothers you, you can easily deactivate it.
travel_delay = -1
    This setting suppresses redrawing until travelling is finished or
    interrupted.
tile_update_rate = 1000
    By default, the screen gets redrawn at least every 1000 milliseconds,
    more often if you take actions that change the display. You could try
    cranking up this value, though this may lead to updating taking too long.
tile_tooltip_ms = 0
    Deactivating the tooltips means there's less stuff to draw every time.
clear_map = false
    Not having to redraw remembered monsters outside your line of sight
    takes some load off the redrawing routines.

tile_window_width   = 1024
tile_window_height  = 768
    The larger the map area the more cells there are to redraw each turn.
    If you've got a large display showing way more than the necessary 17x17
    grids of the map, you could try specifying a lower resolution.