ivl: logic_lpm.c:485: find_local_signal: Assertion `! sig' failed.

[vicencb]

Hi,
this verilog code assigning the same wire to two different ports with different direction through two levels of hierarchy triggers an assertion failure.

module a ();
  wire aw;
  b b_inst ( .first(aw), .second(aw) );
endmodule

module b ( input wire first, output wire second );
  c c_inst ( .first(first), .second(second) );
endmodule

module c ( input wire first, output wire second );
  assign second = 1'b1;
endmodule

To reproduce execute this:
iverilog -tvlog95 test.v

[martinwhitaker]

It seems likely this has the same root cause as #1119, but I'll leave it as a separate issue for now.

[vicencb]

I was trying to use iverilog to unroll generate loops in a project.
The below patch avoids all the failed assertions, but the generated code is still wrong.
For example, the c c_inst ( first, first ); should be c c_inst (first, second);

Then, the generate scopes are printed with the further below patch.

--- a/tgt-vlog95/logic_lpm.c
+++ b/tgt-vlog95/logic_lpm.c
@@ -462,6 +462,7 @@ static void emit_nexus_port_signal(ivl_scope_t scope, ivl_nexus_t nex)
 		  if (scope != ivl_signal_scope(t_sig)) continue;
 		  assert(! sig);
 		  sig = t_sig;
+		  break;
 	    }
       }
 	/* There will not be a signal for an empty port. */
@@ -485,6 +486,7 @@ static ivl_signal_t find_local_signal(const ivl_scope_t scope, ivl_nexus_t nex,
 	    assert(! sig);
 	    sig = t_sig;
 	    *word = ivl_nexus_ptr_pin(nex_ptr);
+	    break;
       }
       return sig;
 }
@@ -512,10 +514,12 @@ void emit_nexus_port_driver_as_ca(ivl_scope_t scope, ivl_nexus_t nex)
 	    if (t_lpm) {
 		  assert(! lpm);
 		  lpm = t_lpm;
+		  break;
 	    }
 	    if (t_net_const) {
 		  assert(! net_const);
 		  net_const = t_net_const;
+		  break;
 	    }
 	    if (t_nlogic) {
 		  assert(! nlogic);
@@ -597,6 +601,7 @@ void emit_nexus_as_ca(ivl_scope_t scope, ivl_nexus_t nex, unsigned allow_UD,
 		  if (t_lpm) {
 			assert(! lpm);
 			lpm = t_lpm;
+			break;
 		  }
 		  if (t_net_const) {
 			if (scope != ivl_const_scope(t_net_const)) {
@@ -885,7 +890,10 @@ static ivl_signal_t nexus_is_signal(ivl_scope_t scope, ivl_nexus_t nex,
 			      *lsb -= ivl_lpm_base(t_lpm);
 			      *msb = *lsb - (int)ivl_lpm_width(t_lpm) + 1;
 			}
-		  } else lpm = t_lpm;
+		  } else {
+			lpm = t_lpm;
+			break;
+		  }
 	    }
 	    if (t_net_const) {
 		  assert(! net_const);

--- a/tgt-vlog95/scope.c
+++ b/tgt-vlog95/scope.c
@@ -1121,13 +1121,9 @@ int emit_scope(ivl_scope_t scope, const ivl_scope_t parent)
 	    emit_named_block_scope(scope);
 	    return 0; /* A named begin/fork is handled in line. */
 	case IVL_SCT_GENERATE:
-	    fprintf(stderr, "%s:%u: vlog95 sorry: generate scopes are not "
-	                    "currently translated \"%s\".\n",
-	                    ivl_scope_file(scope),
-	                    ivl_scope_lineno(scope),
-	                    ivl_scope_tname(scope));
-	    vlog_errors += 1;
-	    return 0;
+	    fprintf(vlog_out, "%*cbegin: ", indent, ' ');
+	    emit_id(ivl_scope_tname(scope));
+	    break;
 	case IVL_SCT_PACKAGE:
 	    assert(indent == 0);
 	    assert(! parent);
@@ -1160,7 +1156,7 @@ int emit_scope(ivl_scope_t scope, const ivl_scope_t parent)
 	    vlog_errors += 1;
 	    return 0;
       }
-      fprintf(vlog_out, ";");
+      if (sc_type != IVL_SCT_GENERATE) fprintf(vlog_out, ";");
       emit_scope_file_line(scope);
       fprintf(vlog_out, "\n");
       indent += indent_incr;
@@ -1168,13 +1164,13 @@ int emit_scope(ivl_scope_t scope, const ivl_scope_t parent)
 	/* Output the scope ports for this scope. */
       if (sc_type == IVL_SCT_MODULE) {
 	    emit_module_port_defs(scope);
-      } else {
+      } else if (sc_type != IVL_SCT_GENERATE) {
 	    emit_task_func_port_defs(scope);
       }
 
       emit_scope_variables(scope);
 
-      if (sc_type == IVL_SCT_MODULE) {
+      if (sc_type == IVL_SCT_MODULE || sc_type == IVL_SCT_GENERATE) {
 	    unsigned count = ivl_scope_lpms(scope);
 	      /* Output the LPM devices. */
 	    for (idx = 0; idx < count; idx += 1) {
@@ -1194,7 +1190,7 @@ int emit_scope(ivl_scope_t scope, const ivl_scope_t parent)
 	    }
       }
 
-      if (sc_type == IVL_SCT_MODULE || sc_type == IVL_SCT_PACKAGE) {
+      if (sc_type == IVL_SCT_MODULE || sc_type == IVL_SCT_PACKAGE || sc_type == IVL_SCT_GENERATE) {
 	      /* Output any initial blocks for tasks or functions or named
 	       * blocks defined in this module. Used to initialize local
 	       * variables. */
@@ -1304,6 +1300,11 @@ int emit_scope(ivl_scope_t scope, const ivl_scope_t parent)
 	    free(package_name);
 	    fprintf(vlog_out, " */\n");
 	    break;
+	case IVL_SCT_GENERATE:
+	    fprintf(vlog_out, "%*cend  /* ", indent, ' ');
+	    emit_id(ivl_scope_tname(scope));
+	    fprintf(vlog_out, " */\n");
+	    break;
 	default:
 	    assert(0);
 	    break;

[martinwhitaker]

Because you have connected b.first and b.second to the same top level wire (aw), the compiler collapses aw, b.first, b.second, c.first, and c.second into a single net. So the vlog95 code generator doesn't know which name to use. But because Verilog also allows port coercion, generating c c_inst(first, first); is valid.

[martinwhitaker]

However, adding a second instance of module b shows a big problem. I'm not sure we can fix this, other than converting the assertions to "sorry, we can't translate this" messages.