Function execute_query_incr_inner 

pub(crate) fn execute_query_incr_inner<'tcx, C: QueryCache>(
    query: &'tcx QueryVTable<'tcx, C>,
    tcx: TyCtxt<'tcx>,
    span: Span,
    key: C::Key,
    mode: QueryMode,
) -> Option<C::Value>

Called by a macro-generated impl of QueryVTable::execute_query_fn, in incremental mode.