Replace assert in abc9_ops with more useful error message

diff --git a/passes/techmap/abc9_ops.cc b/passes/techmap/abc9_ops.cc
index 98d0207c4cecfe72381d2ef6661798143c29fbc5..3f3e667de472ae41f163770be047d9d380454bd5 100644 (file)
--- a/passes/techmap/abc9_ops.cc
+++ b/passes/techmap/abc9_ops.cc
@@ -778,7 +778,15 @@ void prep_xaiger(RTLIL::Module *module, bool dff)
                        continue;
                if (!box_module->get_bool_attribute(ID::abc9_box))
                        continue;
-               log_assert(cell->parameters.empty());
+               if (!cell->parameters.empty())
+                       // At this stage of the ABC9 flow, all modules must be nonparametric, because ABC itself requires concrete netlists, and the presence of
+                       // parameters implies a non-concrete netlist. This error needs some explaining, because there are (at least) two ways to get this:
+                       // 1) You have an (* abc9_box *) parametric whitebox but due to a bug somewhere this hasn't been monomorphised into a concrete blackbox.
+                       //    This is a bug, and a bug report would be welcomed.
+                       // 2) You have an (* abc9_box *) parametric blackbox (e.g. to store associated cell data) but want to provide timing data for ABC9.
+                       //    This is not supported due to the presence of parameters. If you want to store associated cell data for a box, one approach could be
+                       //    to techmap the parameters to constant module inputs, and then after ABC9 use _TECHMAP_CONSTVAL_XX_ to retrieve the values again.
+                       log_error("Black box '%s' is marked (* abc9_box *) and has parameters, which is forbidden in prep_xaiger\n", log_id(cell_name));
                log_assert(box_module->get_blackbox_attribute());
 
                cell->attributes[ID::abc9_box_seq] = box_count++;