Function process_function 

fn process_function(
    module: &mut Module,
    override_map: &HandleVec<Override, Handle<Constant>>,
    layouter: &mut Layouter,
    function: &mut Function,
) -> Result<(), ConstantEvaluatorError>

Replace all override expressions in function with fully-evaluated constants.

Replace all Expression::Overrides in function’s expression arena with the corresponding Expression::Constants, as given in override_map. Replace any expressions whose values are now known with their fully evaluated form.

If h is a Handle<Override>, then override_map[h] is the Handle<Constant> for the override’s final value.