chformal: Add -coverprecond option

This inserts $cover cells to cover the enable signal (precondition)
for the selected formal cells.

Author: georgerennie

passes/cmds/chformal.cc

@@ -55,6 +55,9 @@ struct ChformalPass : public Pass {
 		log("    -skip <N>\n");
 		log("        ignore activation of the constraint in the first <N> clock cycles\n");
 		log("\n");
+		log("    -coverprecond\n");
+		log("        add a cover statement for the precondition (enable signal) of the cells\n");
+		log("\n");
 		log("    -assert2assume\n");
 		log("    -assume2assert\n");
 		log("    -live2fair\n");
@@ -114,6 +117,10 @@ struct ChformalPass : public Pass {
 				mode_arg = atoi(args[++argidx].c_str());
 				continue;
 			}
+			if (mode == 0 && args[argidx] == "-coverprecond") {
+				mode = 'p';
+				continue;
+			}
 			if ((mode == 0 || mode == 'c') && args[argidx] == "-assert2assume") {
 				assert2assume = true;
 				mode = 'c';
@@ -263,6 +270,13 @@ struct ChformalPass : public Pass {
 					cell->setPort(ID::EN, module->LogicAnd(NEW_ID, en, cell->getPort(ID::EN)));
 			}
 			else
+			if (mode =='p')
+			{
+				for (auto cell : constr_cells)
+					module->addCover(NEW_ID, cell->getPort(ID::EN), State::S1,
+						"$auto$coverprecond$" + cell->get_src_attribute());
+			}
+			else
 			if (mode == 'c')
 			{
 				for (auto cell : constr_cells)