Fix errors in constant propagation.

Ensure undriven, multiply-driven, and forced nets are correctly handled
by the constant propagation optimisation pass.

cprop.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998-2010,2012 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 1998-2013 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -163,11 +163,6 @@ void cprop_functor::lpm_mux(Design*des, NetMux*obj)
       if (! sel_nex->drivers_constant())
 	    return;
 
-	// If the select input is assigned or forced, then again there
-	// is nothing we can do here.
-      if (sel_nex->assign_lval())
-	    return;
-
 	// If the constant select is 'bz or 'bx, then give up.
       verinum::V sel_val = sel_nex->driven_value();
       if (sel_val == verinum::Vz || sel_val == verinum::Vx)

link_const.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000-2012 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2000-2013 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -25,8 +25,7 @@
 
 /*
  * Scan the link for drivers. If there are only constant drivers, then
- * the nexus has a known constant value. If there is a supply net,
+ * the nexus has a known constant value.
- * then the nexus again has a known constant value.
  */
 bool Nexus::drivers_constant() const
 {
@@ -35,15 +34,23 @@ bool Nexus::drivers_constant() const
       if (driven_ != NO_GUESS)
 	    return true;
 
+      unsigned constant_drivers = 0;
       for (const Link*cur = first_nlink() ; cur  ;  cur = cur->next_nlink()) {
-	    Link::DIR cur_dir;
 
-	    cur_dir = cur->get_dir();
+	      /* A target of a procedural assign or force statement
+		 can't be treated as constant. */
+	    const NetNet*sig = dynamic_cast<const NetNet*>(cur->get_obj());
+	    if (sig && (sig->peek_lref() > 0)) {
+		  driven_ = VAR;
+		  return false;
+	    }
+
+	    Link::DIR cur_dir = cur->get_dir();
 	    if (cur_dir == Link::INPUT)
 		  continue;
 
 	      /* If this is an input or inout port of a root module,
-		 then the is probably not a constant value. I
+		 then this is probably not a constant value. I
 		 certainly don't know what the value is, anyhow. This
 		 can happen in cases like this:
 
@@ -56,16 +63,9 @@ bool Nexus::drivers_constant() const
 		 outside world. */
 
 	    if (cur_dir == Link::PASSIVE) {
-		  const NetNet*sig;
+		  if (sig == 0 || sig->scope()->parent() != 0)
-
-		  const NetPins*obj = cur->get_obj();
-		  const NetObj*as_obj = dynamic_cast<const NetObj*>(obj);
-		  if (as_obj == 0 || as_obj->scope()->parent() != 0)
 			continue;
 
-		  sig = dynamic_cast<const NetNet*>(cur->get_obj());
-		  assert(sig);
-
 		  if (sig->port_type() == NetNet::NOT_A_PORT)
 			continue;
 
@@ -74,19 +74,22 @@ bool Nexus::drivers_constant() const
 
 		  driven_ = VAR;
 		  return false;
-
 	    }
 
-	      /* If there is a supply net, then this nexus will have a
+	      /* If there is an implicit pullup/pulldown on a net,
-		 constant value independent of any drivers. */
+		 count it as a constant driver. */
-	    if (const NetNet*s = dynamic_cast<const NetNet*>(cur->get_obj()))
+	    if (sig)
-		  switch (s->type()) {
+		  switch (sig->type()) {
 		      case NetNet::SUPPLY0:
+		      case NetNet::TRI0:
+			constant_drivers += 1;
 			driven_ = V0;
-			return true;
+			continue;
 		      case NetNet::SUPPLY1:
+		      case NetNet::TRI1:
+			constant_drivers += 1;
 			driven_ = V1;
-			return true;
+			continue;
 		      default:
 			break;
 		  }
@@ -95,6 +98,18 @@ bool Nexus::drivers_constant() const
 		  driven_ = VAR;
 		  return false;
 	    }
+
+	    constant_drivers += 1;
+      }
+
+	/* If there is more than one constant driver for this nexus, we
+	   would need to resolve the constant value, taking into account
+	   the drive strengths. This is a lot of work for something that
+	   will rarely occur, so for now leave the resolution to be done
+	   at run time. */
+      if (constant_drivers > 1) {
+	    driven_ = VAR;
+	    return false;
       }
 
       return true;
@@ -127,28 +142,25 @@ verinum::V Nexus::driven_value() const
 	    const NetConst*obj;
 	    const NetNet*sig;
 	    if ((obj = dynamic_cast<const NetConst*>(cur->get_obj()))) {
+		    // Multiple drivers are not currently supported.
+		  ivl_assert(*obj, val == verinum::Vz);
 		  val = obj->value(cur->get_pin());
 
 	    } else if ((sig = dynamic_cast<const NetNet*>(cur->get_obj()))) {
 
-		    // If we find an attached SUPPLY0/1, the we know
+		    // If we find an implicit pullup or pulldown on a
-		    // from that what the driven value is. Stop now.
+		    // net, this is a good guess for the driven value,
-		  if (sig->type() == NetNet::SUPPLY0) {
+		    // but keep looking for other drivers.
-			driven_ = V0;
+		  if ((sig->type() == NetNet::SUPPLY0) ||
-			return verinum::V0;
+		      (sig->type() == NetNet::TRI0)) {
-		  }
+			  // Multiple drivers are not currently supported.
-		  if (sig->type() == NetNet::SUPPLY1) {
+			ivl_assert(*obj, val == verinum::Vz);
-			driven_ = V1;
-			return verinum::V1;
-		  }
-
-		    // If we find an attached TRI0/1, then this is a
-		    // good guess for the driven value, but keep
-		    // looking for something better.
-		  if (sig->type() == NetNet::TRI0) {
 			val = verinum::V0;
 		  }
-		  if (sig->type() == NetNet::TRI1) {
+		  if ((sig->type() == NetNet::SUPPLY1) ||
+		      (sig->type() == NetNet::TRI1)) {
+			  // Multiple drivers are not currently supported.
+			ivl_assert(*obj, val == verinum::Vz);
 			val = verinum::V1;
 		  }
 	    }
@@ -179,40 +191,44 @@ verinum Nexus::driven_vector() const
       const Link*cur = list_;
 
       verinum val;
+      unsigned width = 0;
 
       for (cur = first_nlink() ; cur  ;  cur = cur->next_nlink()) {
 
 	    const NetConst*obj;
 	    const NetNet*sig;
 	    if ((obj = dynamic_cast<const NetConst*>(cur->get_obj()))) {
+		    // Multiple drivers are not currently supported.
+		  ivl_assert(*obj, val.len() == 0);
 		  ivl_assert(*obj, cur->get_pin() == 0);
 		  val = obj->value();
+		  width = val.len();
 
 	    } else if ((sig = dynamic_cast<const NetNet*>(cur->get_obj()))) {
 
-		    // If we find an attached SUPPLY0/1, the we know
+		  width = sig->vector_width();
-		    // from that what the driven value is. Stop now.
-		  if (sig->type() == NetNet::SUPPLY0) {
-			driven_ = V0;
-			return verinum(verinum::V0, sig->vector_width());
-		  }
-		  if (sig->type() == NetNet::SUPPLY1) {
-			driven_ = V1;
-			return verinum(verinum::V1, sig->vector_width());
-		  }
 
-		    // If we find an attached TRI0/1, then this is a
+		    // If we find an implicit pullup or pulldown on a
-		    // good guess for the driven value, but keep
+		    // net, this is a good guess for the driven value,
-		    // looking for something better.
+		    // but keep looking for other drivers.
-		  if (sig->type() == NetNet::TRI0) {
+		  if ((sig->type() == NetNet::SUPPLY0) ||
-			val = verinum(verinum::V0, sig->vector_width());
+		      (sig->type() == NetNet::TRI0)) {
+			  // Multiple drivers are not currently supported.
+			ivl_assert(*obj, val.len() == 0);
+			val = verinum(verinum::V0, width);
 		  }
-		  if (sig->type() == NetNet::TRI1) {
+		  if ((sig->type() == NetNet::SUPPLY1) ||
-			val = verinum(verinum::V1, sig->vector_width());
+		      (sig->type() == NetNet::TRI1)) {
+			  // Multiple drivers are not currently supported.
+			ivl_assert(*obj, val.len() == 0);
+			val = verinum(verinum::V1, width);
 		  }
 	    }
       }
 
+	// If we have a width but not a value, this must be an undriven net.
+      if (val.len() != width)
+	    val = verinum(verinum::Vz, width);
+
       return val;
 }
-

net_link.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000-2010 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2000-2013 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -311,16 +311,13 @@ bool Nexus::drivers_present() const
 		  continue;
 
 	      // Must be PASSIVE, so if it is some kind of net, see if
-	      // it is the sort that might drive the nexus.
+	      // it is the sort that might drive the nexus. Note that
+	      // supply0/1 and tri0/1 nets are classified as OUTPUT.
 	    const NetPins*obj;
 	    unsigned pin;
 	    cur->cur_link(obj, pin);
 	    if (const NetNet*net = dynamic_cast<const NetNet*>(obj))
 		  switch (net->type()) {
-		      case NetNet::SUPPLY0:
-		      case NetNet::SUPPLY1:
-		      case NetNet::TRI0:
-		      case NetNet::TRI1:
 		      case NetNet::WAND:
 		      case NetNet::WOR:
 		      case NetNet::TRIAND:

netlist.cc

@@ -479,8 +479,23 @@ PortType::Enum PortType::merged( Enum lhs, Enum rhs )
     return PINOUT;
 }
 
-void NetNet::initialize_dir_(Link::DIR dir)
+void NetNet::initialize_dir_()
 {
+      Link::DIR dir = Link::PASSIVE;
+
+      switch (type_) {
+	  case REG:
+	  case IMPLICIT_REG:
+	  case SUPPLY0:
+	  case SUPPLY1:
+	  case TRI0:
+	  case TRI1:
+	    dir = Link::OUTPUT;
+	    break;
+	  default:
+	    break;
+      }
+
       if (pins_are_virtual()) {
 	    if (0) cerr << "NetNet setting Link default dir" << endl;
 	    set_default_dir(dir);
@@ -564,24 +579,7 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t,
 	    ivl_assert(*this, 0);
       }
 
-      Link::DIR dir = Link::PASSIVE;
+      initialize_dir_();
-
-      switch (t) {
-	  case REG:
-	  case IMPLICIT_REG:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY0:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY1:
-	    dir = Link::OUTPUT;
-	    break;
-	  default:
-	    break;
-      }
-
-      initialize_dir_(dir);
 
       s->add_signal(this);
 }
@@ -600,24 +598,8 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t, netstruct_t*ty)
 {
 	//XXXX packed_dims_.push_back(netrange_t(calculate_count(ty)-1, 0));
       calculate_slice_widths_from_packed_dims_();
-      Link::DIR dir = Link::PASSIVE;
 
-      switch (t) {
+      initialize_dir_();
-	  case REG:
-	  case IMPLICIT_REG:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY0:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY1:
-	    dir = Link::OUTPUT;
-	    break;
-	  default:
-	    break;
-      }
-
-      initialize_dir_(dir);
 
       s->add_signal(this);
 }
@@ -629,24 +611,7 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t, netdarray_t*ty)
     discipline_(0),
     eref_count_(0), lref_count_(0)
 {
-      Link::DIR dir = Link::PASSIVE;
+      initialize_dir_();
-
-      switch (t) {
-	  case REG:
-	  case IMPLICIT_REG:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY0:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY1:
-	    dir = Link::OUTPUT;
-	    break;
-	  default:
-	    break;
-      }
-
-      initialize_dir_(dir);
 
       s->add_signal(this);
 }
@@ -659,24 +624,8 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t, netvector_t*ty)
     eref_count_(0), lref_count_(0)
 {
       calculate_slice_widths_from_packed_dims_();
-      Link::DIR dir = Link::PASSIVE;
 
-      switch (t) {
+      initialize_dir_();
-	  case REG:
-	  case IMPLICIT_REG:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY0:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY1:
-	    dir = Link::OUTPUT;
-	    break;
-	  default:
-	    break;
-      }
-
-      initialize_dir_(dir);
 
       s->add_signal(this);
 }
@@ -712,27 +661,9 @@ void NetNet::type(NetNet::Type t)
       if (type_ == t)
 	    return;
 
-      Link::DIR dir = Link::PASSIVE;
-      switch (t) {
-	  case REG:
-	  case IMPLICIT_REG:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY0:
-	    dir = Link::OUTPUT;
-	    break;
-	  case SUPPLY1:
-	    dir = Link::OUTPUT;
-	    break;
-	  default:
-	    break;
-      }
-
       type_ = t;
-      for (unsigned idx = 0 ;  idx < pin_count() ;  idx += 1) {
-	    pin(idx).set_dir(dir);
-      }
 
+      initialize_dir_();
 }
 
 

netlist.h

@@ -581,9 +581,10 @@ class NetDelaySrc  : public NetObj {
  *
  * NetNet objects are located by searching NetScope objects.
  *
- * The pins of a NetNet object are PASSIVE: they do not drive
+ * The pins of a NetNet object are usually PASSIVE: they do not drive
  * anything and they are not a data sink, per se. The pins follow the
- * values on the nexus.
+ * values on the nexus. The exceptions are reg, trireg, tri0, tri1,
+ * supply0, and supply1 objects, whose pins are classed as OUTPUT.
  */
 
 class PortType
@@ -746,7 +747,7 @@ class NetNet  : public NetObj, public PortType {
       virtual void dump_net(ostream&, unsigned) const;
 
     private:
-      void initialize_dir_(Link::DIR dir);
+      void initialize_dir_();
 
     private:
       Type   type_    : 5;