5 files changed, 10 insertions, 9 deletions
diff --git a/frontends/ast/ast.cc b/frontends/ast/ast.cc
index be04d5536..037a9f3ee 100644
--- a/frontends/ast/ast.cc
+++ b/frontends/ast/ast.cc
@@ -1067,7 +1067,7 @@ AstModule::~AstModule()
 }
 
 // create a new parametric module (when needed) and return the name of the generated module
-RTLIL::IdString AstModule::derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters)
+RTLIL::IdString AstModule::derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters, bool)
 {
 	std::string stripped_name = name.str();
 
diff --git a/frontends/ast/ast.h b/frontends/ast/ast.h
index a5d5ee30a..d1e2c78d1 100644
--- a/frontends/ast/ast.h
+++ b/frontends/ast/ast.h
@@ -283,7 +283,7 @@ namespace AST
 		AstNode *ast;
 		bool nolatches, nomeminit, nomem2reg, mem2reg, lib, noopt, icells, autowire;
 		virtual ~AstModule();
-		virtual RTLIL::IdString derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters);
+		virtual RTLIL::IdString derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters, bool mayfail);
 		virtual RTLIL::Module *clone() const;
 	};
 
diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 3e873054f..fb3d9dbe9 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -639,8 +639,10 @@ RTLIL::Module::~Module()
 		delete it->second;
 }
 
-RTLIL::IdString RTLIL::Module::derive(RTLIL::Design*, dict<RTLIL::IdString, RTLIL::Const>)
+RTLIL::IdString RTLIL::Module::derive(RTLIL::Design*, dict<RTLIL::IdString, RTLIL::Const>, bool mayfail)
 {
+	if (mayfail)
+		return RTLIL::IdString();
 	log_error("Module `%s' is used with parameters but is not parametric!\n", id2cstr(name));
 }
 
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index fc29e1e65..a251b4252 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -906,7 +906,7 @@ public:
 
 	Module();
 	virtual ~Module();
-	virtual RTLIL::IdString derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters);
+	virtual RTLIL::IdString derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters, bool mayfail = false);
 	virtual size_t count_id(RTLIL::IdString id);
 
 	virtual void sort();
diff --git a/passes/hierarchy/hierarchy.cc b/passes/hierarchy/hierarchy.cc
index 524d57854..c680dbbd8 100644
--- a/passes/hierarchy/hierarchy.cc
+++ b/passes/hierarchy/hierarchy.cc
@@ -625,16 +625,15 @@ struct HierarchyPass : public Pass {
 		for (auto module : design->modules())
 		for (auto cell : module->cells())
 		{
-			if (GetSize(cell->parameters) != 0)
-				continue;
-
 			Module *m = design->module(cell->type);
 
 			if (m == nullptr)
 				continue;
 
-			if (m->get_bool_attribute("\\blackbox") && cell->parameters.size()) {
-				IdString new_m_name = m->derive(design, cell->parameters);
+			if (m->get_bool_attribute("\\blackbox") && !cell->parameters.empty()) {
+				IdString new_m_name = m->derive(design, cell->parameters, true);
+				if (new_m_name.empty())
+					continue;
 				if (new_m_name != m->name) {
 					m = design->module(new_m_name);
 					blackbox_derivatives.insert(m);