Function intern_const_alloc_for_constprop 

pub fn intern_const_alloc_for_constprop<'tcx, M: CompileTimeMachine<'tcx>>(
    ecx: &mut InterpCx<'tcx, M>,
    alloc_id: AllocId,
) -> InterpResult<'tcx, ()>

Intern ret. This function assumes that ret references no other allocation.