An input port driven by a variable is not collapsible

PExpr.cc

@@ -72,7 +72,7 @@ NetNet* PExpr::elaborate_bi_net(Design*, NetScope*) const
       return 0;
 }
 
-bool PExpr::is_collapsible_net(Design*, NetScope*) const
+bool PExpr::is_collapsible_net(Design*, NetScope*, NetNet::PortType) const
 {
       return false;
 }

PExpr.h

@@ -1,7 +1,7 @@
 #ifndef IVL_PExpr_H
 #define IVL_PExpr_H
 /*
- * Copyright (c) 1998-2019 Stephen Williams <[email protected]>
+ * Copyright (c) 1998-2020 Stephen Williams <[email protected]>
  * Copyright CERN 2013 / Stephen Williams ([email protected])
  *
  *    This source code is free software; you can redistribute it
@@ -181,7 +181,8 @@ class PExpr : public LineInfo {
         // structural net that can have multiple drivers. This is
         // used to test whether an input port connection can be
         // collapsed to a single wire.
-      virtual bool is_collapsible_net(Design*des, NetScope*scope) const;
+      virtual bool is_collapsible_net(Design*des, NetScope*scope,
+                                      NetNet::PortType port_type) const;
 
 	// This method returns true if that expression is the same as
 	// this expression. This method is used for comparing
@@ -256,7 +257,8 @@ class PEConcat : public PExpr {
 					 NetScope*scope,
 					 bool is_cassign,
 					 bool is_force) const;
-      virtual bool is_collapsible_net(Design*des, NetScope*scope) const;
+      virtual bool is_collapsible_net(Design*des, NetScope*scope,
+                                      NetNet::PortType port_type) const;
     private:
       NetNet* elaborate_lnet_common_(Design*des, NetScope*scope,
 				     bool bidirectional_flag) const;
@@ -377,7 +379,8 @@ class PEIdent : public PExpr {
 
       verinum* eval_const(Design*des, NetScope*sc) const;
 
-      virtual bool is_collapsible_net(Design*des, NetScope*scope) const;
+      virtual bool is_collapsible_net(Design*des, NetScope*scope,
+                                      NetNet::PortType port_type) const;
 
       const PPackage* package() const { return package_; }
 

elab_net.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999-2014 Stephen Williams ([email protected])
+ * Copyright (c) 1999-2020 Stephen Williams ([email protected])
  * Copyright CERN 2012 / Stephen Williams ([email protected])
  *
  *    This source code is free software; you can redistribute it
@@ -168,7 +168,8 @@ NetNet* PEConcat::elaborate_bi_net(Design*des, NetScope*scope) const
       return elaborate_lnet_common_(des, scope, true);
 }
 
-bool PEConcat::is_collapsible_net(Design*des, NetScope*scope) const
+bool PEConcat::is_collapsible_net(Design*des, NetScope*scope,
+                                  NetNet::PortType port_type) const
 {
       assert(scope);
 
@@ -183,7 +184,7 @@ bool PEConcat::is_collapsible_net(Design*des, NetScope*scope) const
 	    if (parms_[idx] == 0)
                   return false;
 
-	    if (!parms_[idx]->is_collapsible_net(des, scope))
+	    if (!parms_[idx]->is_collapsible_net(des, scope, port_type))
                   return false;
       }
 
@@ -1065,7 +1066,8 @@ NetNet*PEIdent::elaborate_unpacked_net(Design*des, NetScope*scope) const
       return sig;
 }
 
-bool PEIdent::is_collapsible_net(Design*des, NetScope*scope) const
+bool PEIdent::is_collapsible_net(Design*des, NetScope*scope,
+                                 NetNet::PortType port_type) const
 {
       assert(scope);
 
@@ -1086,9 +1088,10 @@ bool PEIdent::is_collapsible_net(Design*des, NetScope*scope) const
 	/* If this is SystemVerilog and the variable is not yet
 	   assigned by anything, then convert it to an unresolved
 	   wire. */
-      if (gn_var_can_be_uwire()
-	  && (sig->type() == NetNet::REG)
-	  && (sig->peek_eref() == 0) ) {
+      if (gn_var_can_be_uwire() &&
+          (sig->type() == NetNet::REG) &&
+          (sig->peek_eref() == 0) &&
+          (port_type == NetNet::POUTPUT)) {
 	    sig->type(NetNet::UNRESOLVED_WIRE);
       }
 

elaborate.cc

@@ -1446,18 +1446,20 @@ void PGModule::elaborate_mod_(Design*des, Module*rmod, NetScope*scope) const
 	    assert(prts_vector_width % instance.size() == 0);
 
 	    if (!prts.empty() && (prts[0]->port_type() == NetNet::PINPUT)
-                && prts[0]->pin(0).nexus()->drivers_present()
-                && pins[idx]->is_collapsible_net(des, scope)) {
+	        && prts[0]->pin(0).nexus()->drivers_present()
+	        && pins[idx]->is_collapsible_net(des, scope,
+	                                         prts[0]->port_type())) {
                   prts[0]->port_type(NetNet::PINOUT);
 
 		  cerr << pins[idx]->get_fileline() << ": warning: input port "
 		       << prts[0]->name() << " is coerced to inout." << endl;
 	    }
 
 	    if (!prts.empty() && (prts[0]->port_type() == NetNet::POUTPUT)
-                && (prts[0]->type() != NetNet::REG)
-                && prts[0]->pin(0).nexus()->has_floating_input()
-                && pins[idx]->is_collapsible_net(des, scope)) {
+	        && (prts[0]->type() != NetNet::REG)
+	        && prts[0]->pin(0).nexus()->has_floating_input()
+	        && pins[idx]->is_collapsible_net(des, scope,
+	                                         prts[0]->port_type())) {
                   prts[0]->port_type(NetNet::PINOUT);
 
 		  cerr << pins[idx]->get_fileline() << ": warning: output port "