Give an error if a label is defined but not used.

From-SVN: r171518

gcc/go/gofrontend/gogo.cc

@@ -1463,6 +1463,7 @@ class Check_types_traverse : public Traverse
   Check_types_traverse(Gogo* gogo)
     : Traverse(traverse_variables
 	       | traverse_constants
+	       | traverse_functions
 	       | traverse_statements
 	       | traverse_expressions),
       gogo_(gogo)
@@ -1474,6 +1475,9 @@ class Check_types_traverse : public Traverse
   int
   constant(Named_object*, bool);
 
+  int
+  function(Named_object*);
+
   int
   statement(Block*, size_t* pindex, Statement*);
 
@@ -1542,6 +1546,16 @@ Check_types_traverse::constant(Named_object* named_object, bool)
   return TRAVERSE_CONTINUE;
 }
 
+// There are no types to check in a function, but this is where we
+// issue warnings about labels which are defined but not referenced.
+
+int
+Check_types_traverse::function(Named_object* no)
+{
+  no->func_value()->check_labels();
+  return TRAVERSE_CONTINUE;
+}
+
 // Check that types are valid in a statement.
 
 int
@@ -2744,7 +2758,7 @@ Function::add_label_definition(const std::string& label_name,
 	}
       else
 	{
-	  error_at(location, "redefinition of label %qs",
+	  error_at(location, "label %qs already defined",
 		   Gogo::message_name(label_name).c_str());
 	  inform(label->location(), "previous definition of %qs was here",
 		 Gogo::message_name(label_name).c_str());
@@ -2764,17 +2778,36 @@ Function::add_label_reference(const std::string& label_name)
   if (!ins.second)
     {
       // The label was already in the hash table.
-      return ins.first->second;
+      Label* label = ins.first->second;
+      label->set_is_used();
+      return label;
     }
   else
     {
       gcc_assert(ins.first->second == NULL);
       Label* label = new Label(label_name);
       ins.first->second = label;
+      label->set_is_used();
       return label;
     }
 }
 
+// Warn about labels that are defined but not used.
+
+void
+Function::check_labels() const
+{
+  for (Labels::const_iterator p = this->labels_.begin();
+       p != this->labels_.end();
+       p++)
+    {
+      Label* label = p->second;
+      if (!label->is_used())
+	error_at(label->location(), "label %qs defined and not used",
+		 Gogo::message_name(label->name()).c_str());
+    }
+}
+
 // Swap one function with another.  This is used when building the
 // thunk we use to call a function which calls recover.  It may not
 // work for any other case.

gcc/go/gofrontend/gogo.h

@@ -882,6 +882,10 @@ class Function
   Label*
   add_label_reference(const std::string& label_name);
 
+  // Warn about labels that are defined but not used.
+  void
+  check_labels() const;
+
   // Whether this function calls the predeclared recover function.
   bool
   calls_recover() const
@@ -2090,7 +2094,7 @@ class Label
 {
  public:
   Label(const std::string& name)
-    : name_(name), location_(0), decl_(NULL)
+    : name_(name), location_(0), is_used_(false), decl_(NULL)
   { }
 
   // Return the label's name.
@@ -2103,6 +2107,16 @@ class Label
   is_defined() const
   { return this->location_ != 0; }
 
+  // Return whether the label has been used.
+  bool
+  is_used() const
+  { return this->is_used_; }
+
+  // Record that the label is used.
+  void
+  set_is_used()
+  { this->is_used_ = true; }
+
   // Return the location of the definition.
   source_location
   location() const
@@ -2130,6 +2144,8 @@ class Label
   // The location of the definition.  This is 0 if the label has not
   // yet been defined.
   source_location location_;
+  // Whether the label has been used.
+  bool is_used_;
   // The LABEL_DECL.
   tree decl_;
 };

gcc/go/gofrontend/parse.cc

@@ -3112,7 +3112,7 @@ Parse::unary_expr(bool may_be_sink, bool may_be_composite_lit,
 // LABEL is the label of this statement if it has one.
 
 void
-Parse::statement(const Label* label)
+Parse::statement(Label* label)
 {
   const Token* token = this->peek_token();
   switch (token->classification())
@@ -3288,6 +3288,10 @@ Parse::labeled_stmt(const std::string& label_name, source_location location)
 
   if (!this->statement_may_start_here())
     {
+      // Mark the label as used to avoid a useless error about an
+      // unused label.
+      label->set_is_used();
+
       error_at(location, "missing statement after label");
       this->unget_token(Token::make_operator_token(OPERATOR_SEMICOLON,
 						   location));
@@ -3774,7 +3778,7 @@ Parse::if_stat()
 // TypeSwitchGuard = [ identifier ":=" ] Expression "." "(" "type" ")" .
 
 void
-Parse::switch_stat(const Label* label)
+Parse::switch_stat(Label* label)
 {
   gcc_assert(this->peek_token()->is_keyword(KEYWORD_SWITCH));
   source_location location = this->location();
@@ -3873,7 +3877,7 @@ Parse::switch_stat(const Label* label)
 //   "{" { ExprCaseClause } "}"
 
 Statement*
-Parse::expr_switch_body(const Label* label, Expression* switch_val,
+Parse::expr_switch_body(Label* label, Expression* switch_val,
 			source_location location)
 {
   Switch_statement* statement = Statement::make_switch_statement(switch_val,
@@ -3983,7 +3987,7 @@ Parse::expr_switch_case(bool* is_default)
 //   "{" { TypeCaseClause } "}" .
 
 Statement*
-Parse::type_switch_body(const Label* label, const Type_switch& type_switch,
+Parse::type_switch_body(Label* label, const Type_switch& type_switch,
 			source_location location)
 {
   Named_object* switch_no = NULL;
@@ -4127,7 +4131,7 @@ Parse::type_switch_case(std::vector<Type*>* types, bool* is_default)
 // SelectStat = "select" "{" { CommClause } "}" .
 
 void
-Parse::select_stat(const Label* label)
+Parse::select_stat(Label* label)
 {
   gcc_assert(this->peek_token()->is_keyword(KEYWORD_SELECT));
   source_location location = this->location();
@@ -4435,7 +4439,7 @@ Parse::send_or_recv_stmt(bool* is_send, Expression** channel, Expression** val,
 // Condition = Expression .
 
 void
-Parse::for_stat(const Label* label)
+Parse::for_stat(Label* label)
 {
   gcc_assert(this->peek_token()->is_keyword(KEYWORD_FOR));
   source_location location = this->location();
@@ -4654,7 +4658,7 @@ Parse::range_clause_expr(const Expression_list* vals,
 // Push a statement on the break stack.
 
 void
-Parse::push_break_statement(Statement* enclosing, const Label* label)
+Parse::push_break_statement(Statement* enclosing, Label* label)
 {
   if (this->break_stack_ == NULL)
     this->break_stack_ = new Bc_stack();
@@ -4664,7 +4668,7 @@ Parse::push_break_statement(Statement* enclosing, const Label* label)
 // Push a statement on the continue stack.
 
 void
-Parse::push_continue_statement(Statement* enclosing, const Label* label)
+Parse::push_continue_statement(Statement* enclosing, Label* label)
 {
   if (this->continue_stack_ == NULL)
     this->continue_stack_ = new Bc_stack();
@@ -4697,8 +4701,13 @@ Parse::find_bc_statement(const Bc_stack* bc_stack, const std::string& label)
   for (Bc_stack::const_reverse_iterator p = bc_stack->rbegin();
        p != bc_stack->rend();
        ++p)
+    {
       if (p->second != NULL && p->second->name() == label)
+	{
+	  p->second->set_is_used();
 	  return p->first;
+	}
+    }
   return NULL;
 }
 
@@ -4728,9 +4737,11 @@ Parse::break_stat()
 					  token->identifier());
       if (enclosing == NULL)
 	{
-	  error_at(token->location(),
-		   ("break label %qs not associated with "
-		    "for or switch or select"),
+	  // If there is a label with this name, mark it as used to
+	  // avoid a useless error about an unused label.
+	  this->gogo_->add_label_reference(token->identifier());
+
+	  error_at(token->location(), "invalid break label %qs",
 		   Gogo::message_name(token->identifier()).c_str());
 	  this->advance_token();
 	  return;
@@ -4781,8 +4792,11 @@ Parse::continue_stat()
 					  token->identifier());
       if (enclosing == NULL)
 	{
-	  error_at(token->location(),
-		   "continue label %qs not associated with for",
+	  // If there is a label with this name, mark it as used to
+	  // avoid a useless error about an unused label.
+	  this->gogo_->add_label_reference(token->identifier());
+
+	  error_at(token->location(), "invalid continue label %qs",
 		   Gogo::message_name(token->identifier()).c_str());
 	  this->advance_token();
 	  return;

gcc/go/gofrontend/parse.h

@@ -150,7 +150,7 @@ class Parse
   // For break and continue we keep a stack of statements with
   // associated labels (if any).  The top of the stack is used for a
   // break or continue statement with no label.
-  typedef std::vector<std::pair<Statement*, const Label*> > Bc_stack;
+  typedef std::vector<std::pair<Statement*, Label*> > Bc_stack;
 
   // Parser nonterminals.
   void identifier_list(Typed_identifier_list*);
@@ -220,7 +220,7 @@ class Parse
 			 bool* is_type_switch);
   Expression* qualified_expr(Expression*, source_location);
   Expression* id_to_expression(const std::string&, source_location);
-  void statement(const Label*);
+  void statement(Label*);
   bool statement_may_start_here();
   void labeled_stmt(const std::string&, source_location);
   Expression* simple_stat(bool, bool, Range_clause*, Type_switch*);
@@ -236,26 +236,25 @@ class Parse
   void go_or_defer_stat();
   void return_stat();
   void if_stat();
-  void switch_stat(const Label*);
-  Statement* expr_switch_body(const Label*, Expression*, source_location);
+  void switch_stat(Label*);
+  Statement* expr_switch_body(Label*, Expression*, source_location);
   void expr_case_clause(Case_clauses*, bool* saw_default);
   Expression_list* expr_switch_case(bool*);
-  Statement* type_switch_body(const Label*, const Type_switch&,
-			      source_location);
+  Statement* type_switch_body(Label*, const Type_switch&, source_location);
   void type_case_clause(Named_object*, Type_case_clauses*, bool* saw_default);
   void type_switch_case(std::vector<Type*>*, bool*);
-  void select_stat(const Label*);
+  void select_stat(Label*);
   void comm_clause(Select_clauses*, bool* saw_default);
   bool comm_case(bool*, Expression**, Expression**, Expression**,
 		 std::string*, std::string*, bool*);
   bool send_or_recv_stmt(bool*, Expression**, Expression**, Expression**,
 			 std::string*, std::string*);
-  void for_stat(const Label*);
+  void for_stat(Label*);
   void for_clause(Expression**, Block**);
   void range_clause_decl(const Typed_identifier_list*, Range_clause*);
   void range_clause_expr(const Expression_list*, Range_clause*);
-  void push_break_statement(Statement*, const Label*);
-  void push_continue_statement(Statement*, const Label*);
+  void push_break_statement(Statement*, Label*);
+  void push_continue_statement(Statement*, Label*);
   void pop_break_statement();
   void pop_continue_statement();
   Statement* find_bc_statement(const Bc_stack*, const std::string&);

gcc/testsuite/go.test/test/fixedbugs/bug055.go

@@ -7,16 +7,21 @@
 package main
 
 func main() {
-	var i int;
-	var j int;
-	if true {}
-	{ return }
-	i = 0;
-	if true {} else i++;
-	type s struct {};
-	i = 0;
-	type s2 int;
-	var k = func (a int) int { return a+1 }(3);
-	_, _ = j, k;
-ro: ;
+	var i int
+	var j int
+	if true {
+	}
+	{
+		return
+	}
+	i = 0
+	if true {
+	} else {
+		i++
+	}
+	type s struct{}
+	i = 0
+	type s2 int
+	var k = func(a int) int { return a + 1 }(3)
+	_, _ = j, k
 }

gcc/testsuite/go.test/test/fixedbugs/bug076.go

@@ -1,4 +1,4 @@
-// $G $D/$F.go && $L $F.$A && ./$A.out
+// $G $D/$F.go && $L $F.$A
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,12 +7,16 @@
 package main
 
 func f() {
-exit: ;
+exit:
+	;
+	goto exit
 }
 
 
 func main() {
-exit: ; // this should be legal (labels not properly scoped?)
+exit:
+	; // this should be legal (labels not properly scoped?)
+	goto exit
 }
 
 /*

gcc/testsuite/go.test/test/fixedbugs/bug077.go

@@ -7,7 +7,8 @@
 package main
 
 func main() {
-	var exit int;
+	var exit int
 exit:
-	_ = exit;
+	_ = exit
+	goto exit
 }

gcc/testsuite/go.test/test/fixedbugs/bug091.go

@@ -8,17 +8,18 @@ package main
 
 func f1() {
 exit:
-		print("hi\n");
+	print("hi\n")
+	goto exit
 }
 
 func f2() {
-	const c = 1234;
+	const c = 1234
 }
 
 func f3() {
-	i := c;	// ERROR "undef"
+	i := c // ERROR "undef"
 }
 
 func main() {
-	f3();
+	f3()
 }

gcc/testsuite/go.test/test/fixedbugs/bug137.go

@@ -8,16 +8,21 @@ package main
 
 func main() {
 L1:
-L2:	for i := 0; i < 10; i++ {
-		print(i);
-		break L2;
+L2:
+	for i := 0; i < 10; i++ {
+		print(i)
+		break L2
 	}
 
-L3: ;
-L4:	for i := 0; i < 10; i++ {
-		print(i);
-		break L4;
+L3:
+	;
+L4:
+	for i := 0; i < 10; i++ {
+		print(i)
+		break L4
 	}
+	goto L1
+	goto L3
 }
 
 /*

gcc/testsuite/go.test/test/fixedbugs/bug140.go

@@ -7,8 +7,17 @@
 package main
 
 func main() {
-	if true {} else L1: ;
-	if true {} else L2: main() ;
+	if true {
+	} else {
+	L1:
+	}
+	if true {
+	} else {
+	L2:
+		main()
+	}
+	goto L1
+	goto L2
 }
 
 /*

gcc/testsuite/go.test/test/fixedbugs/bug178.go

@@ -11,17 +11,23 @@ L:
 	for i := 0; i < 1; i++ {
 	L1:
 		for {
-			break L;
+			break L
 		}
-		panic("BUG: not reached - break");
+		panic("BUG: not reached - break")
 	}
 
 L2:
 	for i := 0; i < 1; i++ {
 	L3:
 		for {
-			continue L2;
+			continue L2
 		}
-		panic("BUG: not reached - continue");
+		panic("BUG: not reached - continue")
+	}
+	if false {
+		goto L1
+	}
+	if false {
+		goto L3
 	}
 }

gcc/testsuite/go.test/test/fixedbugs/bug179.go

@@ -10,16 +10,18 @@ func main() {
 L:
 	for {
 		for {
-			break L2;	// ERROR "L2"
-			continue L2;	// ERROR "L2"
+			break L2    // ERROR "L2"
+			continue L2 // ERROR "L2"
 		}
 	}
 
 L1:
-	x := 1;
-	_ = x;
+	x := 1
+	_ = x
 	for {
-		break L1;	// ERROR "L1"
-		continue L1;	// ERROR "L1"
+		break L1    // ERROR "L1"
+		continue L1 // ERROR "L1"
 	}
+
+	goto L
 }

gcc/testsuite/go.test/test/fixedbugs/bug274.go

@@ -24,6 +24,7 @@ func main() {
 	case 1:
 		L1:  // ERROR "statement"
 	default:
-		L2:  // correct since no semicolon is required before a '}'
+		     // correct since no semicolon is required before a '}'
+		L2:  // GCCGO_ERROR "not used"
 	}
 }