Add support for void cast function call

SystemVerilog has explicit support for calling a function
as a statement. This is allowed when the function call is encapsulated in
`void'(...)`. E.g. `void'(f(1, 2, 3));`

We already support calling function calls as statements without the void
cast and emit a warning when doing so.

Adding support for void casts only requires to update the parser to handle
the void cast and then do not emit the warning if a function is called as
a statement as part of a void cast.

Void casting a task or void function call is not allowed and will generate
an elaboration error.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

Statement.h

@@ -226,6 +226,8 @@ class PCallTask  : public Statement {
 
       bool elaborate_elab(Design*des, NetScope*scope) const;
 
+      void void_cast() { void_cast_ = true; }
+
     private:
       NetProc* elaborate_sys(Design*des, NetScope*scope) const;
       NetProc* elaborate_usr(Design*des, NetScope*scope) const;
@@ -257,6 +259,7 @@ class PCallTask  : public Statement {
       PPackage*package_;
       pform_name_t path_;
       std::vector<PExpr*> parms_;
+      bool void_cast_ = false;
 };
 
 class PCase  : public Statement {

elaborate.cc

@@ -3390,10 +3390,14 @@ NetProc* PCondit::elaborate(Design*des, NetScope*scope) const
 
 NetProc* PCallTask::elaborate(Design*des, NetScope*scope) const
 {
-      if (peek_tail_name(path_)[0] == '$')
+      if (peek_tail_name(path_)[0] == '$') {
-	    return elaborate_sys(des, scope);
+	    if (void_cast_)
+		  return elaborate_non_void_function_(des, scope);
 	    else
+		  return elaborate_sys(des, scope);
+      } else {
 	    return elaborate_usr(des, scope);
+      }
 }
 
 /*
@@ -3690,8 +3694,10 @@ NetProc* PCallTask::elaborate_method_func_(NetScope*scope,
 					   perm_string method_name,
                                            const char*sys_task_name) const
 {
+      if (!void_cast_) {
 	    cerr << get_fileline() << ": warning: method function '"
 		 << method_name << "' is being called as a task." << endl;
+      }
 
 	// Generate the function.
       NetESFunc*sys_expr = new NetESFunc(sys_task_name, type, 1);
@@ -3906,8 +3912,11 @@ NetProc *PCallTask::elaborate_non_void_function_(Design *des, NetScope *scope) c
       PAssign*tmp = new PAssign(0, rval);
       tmp->set_file(get_file());
       tmp->set_lineno(get_lineno());
+      if (!void_cast_) {
 	    cerr << get_fileline() << ": warning: User function '"
 		 << peek_tail_name(path_) << "' is being called as a task." << endl;
+      }
+
 	// Elaborate the assignment to a dummy variable.
       return tmp->elaborate(des, scope);
 }
@@ -3962,11 +3971,23 @@ NetProc* PCallTask::elaborate_build_call_(Design*des, NetScope*scope,
 	      // that we can catch more errors.
 	    test_task_calls_ok_(des, scope);
 
+	    if (void_cast_) {
+		  cerr << get_fileline() << ": error: void casting user task '"
+		       << peek_tail_name(path_) << "' is not allowed." << endl;
+		  des->errors++;
+	    }
+
       } else if (task->type() == NetScope::FUNC) {
 	    NetFuncDef*tmp = task->func_def();
 	    if (!tmp->is_void())
 		  return elaborate_non_void_function_(des, scope);
 	    def = tmp;
+
+	    if (void_cast_) {
+		  cerr << get_fileline() << ": error: void casting user void function '"
+		       << peek_tail_name(path_) << "' is not allowed." << endl;
+		  des->errors++;
+	    }
       }
 
 	/* The caller has checked the parms_ size to make sure it

parse.y

@@ -420,6 +420,8 @@ static void current_function_set_statement(const YYLTYPE&loc, std::vector<Statem
       PWire*wire;
       std::vector<PWire*>*wires;
 
+      PCallTask *subroutine_call;
+
       PEventStatement*event_statement;
       Statement*statement;
       std::vector<Statement*>*statement_list;
@@ -685,6 +687,8 @@ static void current_function_set_statement(const YYLTYPE&loc, std::vector<Statem
 
 %type <statement> analog_statement
 
+%type <subroutine_call> subroutine_call
+
 %type <join_keyword> join_keyword
 
 %type <letter> spec_polarity
@@ -6241,6 +6245,35 @@ spec_notifier
 		{ args_after_notifier = 0; delete[]$1; }
 	;
 
+subroutine_call
+  : hierarchy_identifier argument_list_parens_opt
+      { PCallTask*tmp = pform_make_call_task(@1, *$1, *$2);
+	delete $1;
+	delete $2;
+	$$ = tmp;
+      }
+  | class_hierarchy_identifier argument_list_parens_opt
+      { PCallTask*tmp = new PCallTask(*$1, *$2);
+	FILE_NAME(tmp, @1);
+	delete $1;
+	delete $2;
+	$$ = tmp;
+      }
+  | SYSTEM_IDENTIFIER argument_list_parens_opt
+      { PCallTask*tmp = new PCallTask(lex_strings.make($1), *$2);
+	FILE_NAME(tmp,@1);
+	delete[]$1;
+	delete $2;
+	$$ = tmp;
+      }
+  | hierarchy_identifier '(' error ')'
+      { yyerror(@3, "error: Syntax error in task arguments.");
+	list<PExpr*>pt;
+	PCallTask*tmp = pform_make_call_task(@1, *$1, pt);
+	delete $1;
+	$$ = tmp;
+      }
+  ;
 
 statement_item /* This is roughly statement_item in the LRM */
 
@@ -6592,19 +6625,13 @@ statement_item /* This is roughly statement_item in the LRM */
 		  FILE_NAME(tmp,@1);
 		  $$ = tmp;
 		}
-	| SYSTEM_IDENTIFIER argument_list_parens_opt ';'
+  | K_void '\'' '(' subroutine_call ')' ';'
-		{ PCallTask*tmp = new PCallTask(lex_strings.make($1), *$2);
+      { $4->void_cast();
-		  FILE_NAME(tmp,@1);
+	$$ = $4;
-		  delete[]$1;
-		  delete $2;
-		  $$ = tmp;
       }
 
-  | hierarchy_identifier argument_list_parens_opt ';'
+  | subroutine_call ';'
-      { PCallTask*tmp = pform_make_call_task(@1, *$1, *$2);
+      { $$ = $1;
-	delete $1;
-	delete $2;
-	$$ = tmp;
       }
 
   | hierarchy_identifier K_with '{' constraint_block_item_list_opt '}' ';'
@@ -6622,14 +6649,6 @@ statement_item /* This is roughly statement_item in the LRM */
 	$$ = tmp;
       }
 
-  | class_hierarchy_identifier argument_list_parens_opt ';'
-      { PCallTask*tmp = new PCallTask(*$1, *$2);
-	FILE_NAME(tmp, @1);
-	delete $1;
-	delete $2;
-	$$ = tmp;
-      }
-
     /* IEEE1800 A.1.8: class_constructor_declaration with a call to
        parent constructor. Note that the implicit_class_handle must
        be K_super ("this.new" makes little sense) but that would
@@ -6646,14 +6665,6 @@ statement_item /* This is roughly statement_item in the LRM */
 	delete $1;
 	$$ = tmp;
       }
-  | hierarchy_identifier '(' error ')' ';'
-      { yyerror(@3, "error: Syntax error in task arguments.");
-	list<PExpr*>pt;
-	PCallTask*tmp = pform_make_call_task(@1, *$1, pt);
-	delete $1;
-	$$ = tmp;
-      }
-
   | error ';'
       { yyerror(@2, "error: malformed statement");
 	yyerrok;