Don't make useless arrays of nexa

When a pin array is virtual, dll_target::signal() doesn't need
to make a corresponding set of stub nexa.

This patch includes new detection of oversized arrays, configurable
with the ARRAY_SIZE_LIMIT flag.  This limit only applies to devirtualized
arrays; virtual arrays are only limited by your architecture's
unsigned int type.

The concept and earlier versions of this patch have been successfully
stress-tested by multiple people.  This one causes no testsuite
regressions on my machine.

Closes: pr2023076
(cherry picked from commit 3a18bda8ee)

compiler.h

@@ -92,6 +92,9 @@ extern bool debug_optimizer;
 /* Possibly temporary flag to control virtualization of pin arrays */
 extern bool disable_virtual_pins;
 
+/* Limit to size of devirtualized arrays */
+extern unsigned long array_size_limit;
+
 /* Path to a directory useful for finding subcomponents. */
 extern const char*basedir;
 

elab_sig.cc

@@ -843,8 +843,8 @@ void PWhile::elaborate_sig(Design*des, NetScope*scope) const
 /*
  * Elaborate a source wire. The "wire" is the declaration of wires,
  * registers, ports and memories. The parser has already merged the
- * multiple properties of a wire (i.e., "input wire") so come the
- * elaboration this creates an object in the design that represent the
+ * multiple properties of a wire (i.e., "input wire"), so come the
+ * elaboration this creates an object in the design that represents the
  * defined item.
  */
 NetNet* PWire::elaborate_sig(Design*des, NetScope*scope) const
@@ -1108,6 +1108,8 @@ NetNet* PWire::elaborate_sig(Design*des, NetScope*scope) const
 	    ? new NetNet(scope, name_, wtype, msb, lsb, array_s0, array_e0)
 	    : new NetNet(scope, name_, wtype, msb, lsb);
 
+      if (wtype == NetNet::WIRE) sig->devirtualize_pins();
+
       ivl_variable_type_t use_data_type = data_type_;
       if (use_data_type == IVL_VT_NO_TYPE) {
 	    use_data_type = IVL_VT_LOGIC;

main.cc

@@ -131,7 +131,8 @@ bool debug_optimizer = false;
 /*
  * Miscellaneous flags.
  */
-bool disable_virtual_pins = false;  // XXX needs a way for user to set
+bool disable_virtual_pins = false;
+unsigned long array_size_limit = 16777216;  // Minimum required by IEEE-1364?
 
 /*
  * Verbose messages enabled.
@@ -714,8 +715,10 @@ int main(int argc, char*argv[])
 	    cout << endl << "PARSING INPUT" << endl;
       }
 
-      const char *flag_dvp = flags["DISABLE_VIRTUAL_PINS"];
-      if (flag_dvp) disable_virtual_pins = strcmp(flag_dvp,"true")==0;
+      const char *flag_tmp = flags["DISABLE_VIRTUAL_PINS"];
+      if (flag_tmp) disable_virtual_pins = strcmp(flag_tmp,"true")==0;
+      flag_tmp = flags["ARRAY_SIZE_LIMIT"];
+      if (flag_tmp) array_size_limit = strtoul(flag_tmp,NULL,0);
 
 	/* Parse the input. Make the pform. */
       int rc = pform_parse(argv[optind]);

netlist.cc

@@ -175,6 +175,12 @@ Link* find_next_output(Link*lnk)
 void NetPins::devirtualize_pins(void)
 {
       if (pins_) return;
+      if (npins_ > array_size_limit) {
+	    cerr << get_fileline() << ": error: pin count " << npins_ <<
+		" exceeds " << array_size_limit <<
+		" (set by -pARRAY_SIZE_LIMIT)" << endl;
+	    assert(0);
+      }
       if (debug_optimizer && npins_ > 1000) cerr << "debug: devirtualizing " << npins_ << " pins." << endl;
 
       pins_ = new Link[npins_];
@@ -263,6 +269,11 @@ bool NetPins::is_linked(void)
 NetObj::NetObj(NetScope*s, perm_string n, unsigned np)
 : NetPins(np), scope_(s), name_(n), delay1_(0), delay2_(0), delay3_(0)
 {
+      /* Don't 
+      ivl_assert(*this, np > 0);
+       * because it would happen before we get to print a useful
+       * message in the NetNet constructor
+       */
 }
 
 NetObj::~NetObj()
@@ -568,12 +579,14 @@ static unsigned calculate_count(long s, long e)
 {
       unsigned long r;
       if (s >= e) {
-	    r = s - e + 1;
+	    r = s - e;
       } else {
-	    r = e - s + 1;
+	    r = e - s;
       }
-      assert (r <= UINT_MAX);
-      return r;
+      if (r >= UINT_MAX) {
+	    return 0;
+      }
+      return r + 1;
 }
 
 NetNet::NetNet(NetScope*s, perm_string n, Type t,
@@ -584,7 +597,11 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t,
     discipline_(0), msb_(ms), lsb_(ls), dimensions_(1), s0_(array_s), e0_(array_e),
     local_flag_(false), eref_count_(0), lref_count_(0)
 {
-      assert(s);
+      ivl_assert(*this, s);
+      if (pin_count() == 0) {
+	    cerr << "Array too big [" << array_s << ":" << array_e << "]" << endl;
+	    ivl_assert(*this, 0);
+      }
 
       verinum::V init_value = verinum::Vz;
       Link::DIR dir = Link::PASSIVE;
@@ -778,7 +795,9 @@ bool NetNet::array_addr_swapped() const
 
 unsigned NetNet::array_count() const
 {
-      return calculate_count(s0_, e0_);
+      unsigned c = calculate_count(s0_, e0_);
+      ivl_assert(*this, c > 0);
+      return c;
 }
 
 bool NetNet::array_index_is_valid(long sb) const

netlist.h

@@ -197,10 +197,10 @@ class NetPins : public LineInfo {
       void set_default_init(verinum::V val);
       bool is_linked();
       bool pins_are_virtual(void) const;
+      void devirtualize_pins(void);
 
     private:
       Link*pins_;
-      void devirtualize_pins(void);
       const unsigned npins_;
       Link::DIR default_dir_;
       verinum::V default_init_;

t-dll-api.cc

@@ -1893,10 +1893,16 @@ extern "C" const char* ivl_signal_name(ivl_signal_t net)
 extern "C" ivl_nexus_t ivl_signal_nex(ivl_signal_t net, unsigned word)
 {
       assert(word < net->array_words);
-      if (net->array_words > 1)
-	    return net->pins[word];
-      else
+      if (net->array_words > 1) {
+	    if (net->pins) {
+		return net->pins[word];
+	    } else {
+		cerr << "AACK! ivl_signal_nex() returning NULL" << endl;
+		return NULL;
+	    }
+      } else {
 	    return net->pin;
+      }
 }
 
 extern "C" int ivl_signal_msb(ivl_signal_t net)

t-dll.cc

@@ -2564,6 +2564,12 @@ void dll_target::signal(const NetNet*net)
       assert(obj->array_words == net->pin_count());
       if (debug_optimizer && obj->array_words > 1000) cerr << "debug: "
 	    "t-dll creating nexus array " << obj->array_words << " long" << endl;
+      if (obj->array_words > 1 && net->pins_are_virtual()) {
+	    obj->pins = NULL;
+	    if (debug_optimizer && obj->array_words > 1000) cerr << "debug: "
+		"t-dll used NULL for big nexus array" << endl;
+	    return;
+      }
       if (obj->array_words > 1)
 	    obj->pins = new ivl_nexus_t[obj->array_words];