Merge pull request #900 from larsclausen/task-return

Support return in tasks

elaborate.cc

@@ -2977,6 +2977,9 @@ NetProc* PBlock::elaborate(Design*des, NetScope*scope) const
 	    return tmp;
       }
 
+      if (type != NetBlock::SEQU)
+	    des->fork_enter();
+
       for (unsigned idx = 0 ;  idx < list_.size() ;  idx += 1) {
 	    assert(list_[idx]);
 
@@ -3018,6 +3021,9 @@ NetProc* PBlock::elaborate(Design*des, NetScope*scope) const
 	    cur->append(tmp);
       }
 
+      if (type != NetBlock::SEQU)
+	    des->fork_exit();
+
 	// Update flags in parent scope.
       if (!nscope->is_const_func())
 	    scope->is_const_func(false);
@@ -5763,23 +5769,27 @@ NetProc* PRepeat::elaborate(Design*des, NetScope*scope) const
 NetProc* PReturn::elaborate(Design*des, NetScope*scope) const
 {
       NetScope*target = scope;
+
+      if (des->is_in_fork()) {
+	    cerr << get_fileline() << ": error: "
+		 << "Return statement is not allowed within fork-join block." << endl;
+	    des->errors += 1;
+	    return 0;
+      }
+
       for (;;) {
 	    if (target == 0) {
 		  cerr << get_fileline() << ": error: "
-		       << "Return statement is not in a function." << endl;
+		       << "Return statement is not in a function or task."
+		       << endl;
 		  des->errors += 1;
 		  return 0;
 	    }
 
 	    if (target->type() == NetScope::FUNC)
 		  break;
-
-	    if (target->type() == NetScope::TASK) {
-		  cerr << get_fileline() << ": error: "
-		       << "Cannot \"return\" from tasks." << endl;
-		  des->errors += 1;
-		  return 0;
-	    }
+	    if (target->type() == NetScope::TASK)
+		  break;
 
 	    if (target->type()==NetScope::BEGIN_END) {
 		  target = target->parent();
@@ -5791,6 +5801,19 @@ NetProc* PReturn::elaborate(Design*des, NetScope*scope) const
 	    des->errors += 1;
 	    return 0;
       }
+
+      if (target->type() == NetScope::TASK) {
+	    if (expr_) {
+		  cerr << get_fileline() << ": error: "
+		       << "A value cannot be returned from a task." << endl;
+		  des->errors += 1;
+		  return 0;
+	    }
+	    NetDisable *disa = new NetDisable(target, true);
+	    disa->set_line(*this);
+	    return disa;
+      }
+
       ivl_assert(*this, target->type() == NetScope::FUNC);
 
       if (target->func_def()->is_void()) {

ivtest/ivltests/task_return1.v

@@ -0,0 +1,31 @@
+// Check that it is possible to exit from a task using the return statement with
+// affecting other concurrently running instances of the same task.
+
+module test;
+
+  task automatic t(input integer a, output integer b);
+    if (a == 0) begin
+      b = 1;
+      return;
+    end
+    #10
+    b = 100;
+  endtask
+
+  integer b1;
+  integer b2;
+
+  initial begin
+    fork
+      t(0, b1);
+      t(1, b2);
+    join
+
+    if (b1 == 1 && b2 == 100) begin
+      $display("PASSED");
+    end else begin
+      $display("FAILED b1=%0d, b2=%0d", b1, b2);
+    end
+  end
+
+endmodule

ivtest/ivltests/task_return2.v

@@ -0,0 +1,22 @@
+// Check that it is possible to return from a named sub-block of a task using a
+// `return` statement.
+
+module test;
+
+  task t(input integer a);
+    begin : subblock
+      if (a == 1) begin : condition
+        return;
+      end
+    end
+    $display("FAILED");
+    $finish;
+  endtask
+
+  initial begin
+    t(1);
+    #10
+    $display("PASSED");
+  end
+
+endmodule

ivtest/ivltests/task_return_fail1.v

@@ -0,0 +1,15 @@
+// Check that using a return value when using the return statement in a task
+// results in an error.
+
+module test;
+
+  task t;
+    return 10; // This is an error, tasks can not have return values.
+  endtask
+
+  initial begin
+    t();
+    $display("FAILED");
+  end
+
+endmodule

ivtest/ivltests/task_return_fail2.v

@@ -0,0 +1,18 @@
+// Check that using a return statment inside a parallel block in a task results
+// in an error.
+
+module test;
+
+  task t;
+    fork
+      // This is an error it is not possible to return from inside a parallel block
+      return;
+    join
+  endtask
+
+  initial begin
+    t();
+    $display("FAILED");
+  end
+
+endmodule

ivtest/regress-vvp.list

@@ -38,3 +38,7 @@ sv_array_cassign7		vvp_tests/sv_array_cassign7.json
 sv_foreach9			vvp_tests/sv_foreach9.json
 sv_foreach10			vvp_tests/sv_foreach10.json
 sdf_header			vvp_tests/sdf_header.json
+task_return1			vvp_tests/task_return1.json
+task_return2			vvp_tests/task_return2.json
+task_return_fail1		vvp_tests/task_return_fail1.json
+task_return_fail2		vvp_tests/task_return_fail2.json

ivtest/vvp_tests/task_return1.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "normal",
+    "source"        : "task_return1.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}

ivtest/vvp_tests/task_return2.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "normal",
+    "source"        : "task_return2.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}

ivtest/vvp_tests/task_return_fail1.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "CE",
+    "source"        : "task_return_fail1.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}

ivtest/vvp_tests/task_return_fail2.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "CE",
+    "source"        : "task_return_fail2.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}

netlist.h

@@ -5124,6 +5124,12 @@ class Design {
 	// detected. It prevents code being emitted.
       unsigned errors;
 
+      void fork_enter() { in_fork++; };
+      void fork_exit() { in_fork--; };
+      bool is_in_fork() { return in_fork != 0; }
+
+      unsigned int in_fork = 0;
+
     private:
       NetScope* find_scope_(NetScope*, const hname_t&name,
                             NetScope::TYPE type = NetScope::MODULE) const;