diff mbox

[C++0x] avoid extra tentative parse in range-based for loops

Message ID AANLkTinOGbM81pMy4yE5-mPXJ3aHG8iRmnHtXF+qoMud@mail.gmail.com
State New
Headers show

Commit Message

Rodrigo Rivas Oct. 29, 2010, 12:27 p.m. UTC 
Hi.

I've been thinking for a time about the issue discussed in
http://gcc.gnu.org/ml/gcc/2010-09/msg00379.html
and I think I've got a solution!

The attached patch accomplishes the following:

1. It avoids the additional tentative parse for a range-for.

2. The following code compiles in both C++98 and C++0x modes, just as before.

for (struct S {} s; ; ) ;

3. It emits a helpful error message "range-based-for loops are not
allowed in C++98 mode" if the user tries to compile a range-for in
C++98.

Known side effects of this patch are:
1. The following code:

int a[5];
for (struct S {} s : a) ;

emits "error: expected initializer before : token" both in C++98 and
C++0x, instead of "types may not be defined in range-based for loops".

2. When parsing a for loop, some parser errors previously detected in
cp_parser_simple_declaration are delayed, and so the message may be
different:

for (int a ! ;;) ;

Will say "error: expected ‘;’ before ‘!’ token" instead of "error:
expected initializer before ‘!’ token".


The parsing code for the 'for' statement is now somewhat simpler, but
that's because some of the complexity is moved to
cp_parser_simple_declaration and cp_parser_init_declarator.

Instead of dividing cp_parser_simple_declaration into pieces (too many
and too complex) I decided to add a new parameter and use it as a flag
to skip or modify certain code.
So, if this new parameter, named "just_one_declarator" is NULL, it
behaves exactly as before. But if it is not NULL it will recognize and
return only declarations suitable for a range-for. Again if the
declaration is not suitable for a range-for it will fall back to the
standard behavior.

Then, another tricky part is that the declaration is parsed before we
know if it will be a c-for or a range-for, but it must be declared
into the for scope, and this scope is created at the same time than
the statement. So I created a new function, begin_for_scope, that
creates the scope without the statement, and added the corresponding
parameters to begin_for_stmt and begin_range_for_stmt.

Also, I corrected two typos in a testcase, but that makes no difference.

Jason, what do you think or this?

Regards.
Rodrigo

gcc/cp/

2010-10-29  Rodrigo Rivas Costa <rodrigorivascosta@gmail.com>

	* cp-tree.h (begin_for_scope): New prototype.
	(begin_for_stmt): Update prototype.
	(begin_range_for_stmt): Update prototype.
	* init.c (build_vec_init): Update call to begin_for_stmt.
	* parser.c (enum kind_of_for_loop): New.
	(cp_parser_for): New.
	(cp_parser_c_for): Add three new parameters.
	(cp_parser_range_for): Likewise. Most parsing code removed.
	(cp_parser_iteration_statement): Call cp_parser_for instead of
	cp_parser_c_for and cp_parser_range_for.
	(cp_parser_for_init_statement): Add new parameter and return type.
	(cp_parser_block_declaration): Update call to
	cp_parser_simple_declaration.
	(cp_parser_simple_declaration): Add new parameter.
	Update call to cp_parser_init_declarator.
	(cp_parser_init_declarator): Add new parameter.
	* pt.c (tsubst_expr): Update call to begin_for_stmt.
	* semantics.c (begin_for_scope): New.
	(begin_for_stmt): Add two new parameters.
	(begin_range_for_stmt): Likewise.

gcc/testsuite/

2010-10-20  Rodrigo Rivas Costa <rodrigorivascosta@gmail.com>

	* g++.dg/cpp0x/range-for4.C: Delete include.
	Delete duplicated comment.

Comments

Jason Merrill Nov. 15, 2010, 2:27 p.m. UTC | #1 
On 10/29/2010 08:27 AM, Rodrigo Rivas wrote:
> I've been thinking for a time about the issue discussed in
> http://gcc.gnu.org/ml/gcc/2010-09/msg00379.html
> and I think I've got a solution!

At the standards committee meeting last week I proposed changing 
type-specifier-seq to decl-specifier-seq in the range-based for loop 
(http://open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1204), and 
people agreed.  The change hasn't gone into the WP yet, but I expect it 
will at the next meeting.  Can you update your patch accordingly?

Looking back, it looks like I didn't mention that I was going to suggest 
this; sorry for not keeping you in the loop.

Jason
diff mbox

Patch

diff --git gcc/cp/cp-tree.h gcc/cp/cp-tree.h
index 7595b6f..bd7be14 100644
--- gcc/cp/cp-tree.h
+++ gcc/cp/cp-tree.h
@@ -5222,12 +5222,13 @@  extern tree begin_do_stmt			(void);
 extern void finish_do_body			(tree);
 extern void finish_do_stmt			(tree, tree);
 extern tree finish_return_stmt			(tree);
-extern tree begin_for_stmt			(void);
+extern tree begin_for_scope			(tree *);
+extern tree begin_for_stmt			(tree, tree);
 extern void finish_for_init_stmt		(tree);
 extern void finish_for_cond			(tree, tree);
 extern void finish_for_expr			(tree, tree);
 extern void finish_for_stmt			(tree);
-extern tree begin_range_for_stmt		(void);
+extern tree begin_range_for_stmt		(tree, tree);
 extern void finish_range_for_decl		(tree, tree, tree);
 extern void finish_range_for_stmt		(tree);
 extern tree finish_break_stmt			(void);
diff --git gcc/cp/init.c gcc/cp/init.c
index 3a6e2e7..b7ca123 100644
--- gcc/cp/init.c
+++ gcc/cp/init.c
@@ -3049,7 +3049,7 @@  build_vec_init (tree base, tree maxindex, tree init,
       tree elt_init;
       tree to;
 
-      for_stmt = begin_for_stmt ();
+      for_stmt = begin_for_stmt (NULL_TREE, NULL_TREE);
       finish_for_init_stmt (for_stmt);
       finish_for_cond (build2 (NE_EXPR, boolean_type_node, iterator,
 			       build_int_cst (TREE_TYPE (iterator), -1)),
diff --git gcc/cp/parser.c gcc/cp/parser.c
index 360e197..249cc2d 100644
--- gcc/cp/parser.c
+++ gcc/cp/parser.c
@@ -270,6 +270,12 @@  typedef enum required_token {
   RT_CLASS_TYPENAME_TEMPLATE /* class, typename, or template */
 } required_token;
 
+typedef enum kind_of_for_loop
+{
+  FOR_LOOP_EXPRESSION,
+  FOR_LOOP_DECLARATION,
+  FOR_LOOP_RANGE
+} kind_of_for_loop;
 /* Prototypes.  */
 
 static cp_lexer *cp_lexer_new_main
@@ -1837,12 +1843,14 @@  static tree cp_parser_condition
   (cp_parser *);
 static tree cp_parser_iteration_statement
   (cp_parser *);
-static void cp_parser_for_init_statement
-  (cp_parser *);
-static tree  cp_parser_c_for
-  (cp_parser *);
-static tree  cp_parser_range_for
+static kind_of_for_loop cp_parser_for_init_statement
+  (cp_parser *, tree *decl);
+static tree cp_parser_for
   (cp_parser *);
+static tree cp_parser_c_for
+  (cp_parser *, tree, tree, kind_of_for_loop);
+static tree cp_parser_range_for
+  (cp_parser *, tree, tree, tree);
 static tree cp_parser_jump_statement
   (cp_parser *);
 static void cp_parser_declaration_statement
@@ -1862,7 +1870,7 @@  static void cp_parser_declaration
 static void cp_parser_block_declaration
   (cp_parser *, bool);
 static void cp_parser_simple_declaration
-  (cp_parser *, bool);
+  (cp_parser *, bool, tree *);
 static void cp_parser_decl_specifier_seq
   (cp_parser *, cp_parser_flags, cp_decl_specifier_seq *, int *);
 static tree cp_parser_storage_class_specifier_opt
@@ -1912,7 +1920,7 @@  static tree cp_parser_decltype
 /* Declarators [gram.dcl.decl] */
 
 static tree cp_parser_init_declarator
-  (cp_parser *, cp_decl_specifier_seq *, VEC (deferred_access_check,gc)*, bool, bool, int, bool *);
+  (cp_parser *, cp_decl_specifier_seq *, VEC (deferred_access_check,gc)*, bool, bool, int, bool *, tree *);
 static cp_declarator *cp_parser_declarator
   (cp_parser *, cp_parser_declarator_kind, int *, bool *, bool);
 static cp_declarator *cp_parser_direct_declarator
@@ -8618,20 +8626,38 @@  cp_parser_condition (cp_parser* parser)
 /* Parses a traditional for-statement until the closing ')', not included. */
 
 static tree
-cp_parser_c_for (cp_parser *parser)
+cp_parser_for (cp_parser *parser)
+{
+  tree init, scope, decl;
+  kind_of_for_loop kind;
+
+  /* Begin the for-statement.  */
+  scope = begin_for_scope (&init);
+
+  /* Parse the initialization.  */
+  kind = cp_parser_for_init_statement (parser, &decl);
+
+  if (kind == FOR_LOOP_RANGE)
+    return cp_parser_range_for (parser, scope, init, decl);
+  else
+    return cp_parser_c_for (parser, scope, init, kind);
+}
+
+static tree
+cp_parser_c_for (cp_parser *parser, tree scope, tree init, 
+		 kind_of_for_loop kind)
 {
   /* Normal for loop */
-  tree stmt;
   tree condition = NULL_TREE;
   tree expression = NULL_TREE;
+  tree stmt;
 
-  /* Begin the for-statement.  */
-  stmt = begin_for_stmt ();
+  stmt = begin_for_stmt (scope, init);
 
-  /* Parse the initialization.  */
-  cp_parser_for_init_statement (parser);
-  finish_for_init_stmt (stmt);
+  if (kind == FOR_LOOP_EXPRESSION)
+    cp_parser_expression_statement (parser, NULL_TREE);
 
+  finish_for_init_stmt (stmt);
   /* If there's a condition, process it.  */
   if (cp_lexer_next_token_is_not (parser->lexer, CPP_SEMICOLON))
     condition = cp_parser_condition (parser);
@@ -8659,48 +8685,10 @@  cp_parser_c_for (cp_parser *parser)
   Returns TRUE iff a range-based for is parsed. */
 
 static tree
-cp_parser_range_for (cp_parser *parser)
+cp_parser_range_for (cp_parser *parser, tree scope, tree init, tree range_decl)
 {
-  tree stmt, range_decl, range_expr;
-  cp_decl_specifier_seq type_specifiers;
-  cp_declarator *declarator;
-  const char *saved_message;
-  tree attributes, pushed_scope;
-
-  cp_parser_parse_tentatively (parser);
-  /* New types are not allowed in the type-specifier-seq for a
-     range-based for loop.  */
-  saved_message = parser->type_definition_forbidden_message;
-  parser->type_definition_forbidden_message
-    = G_("types may not be defined in range-based for loops");
-  /* Parse the type-specifier-seq.  */
-  cp_parser_type_specifier_seq (parser, /*is_declaration==*/true,
-				/*is_trailing_return=*/false,
-				&type_specifiers);
-  /* Restore the saved message.  */
-  parser->type_definition_forbidden_message = saved_message;
-  /* If all is well, we might be looking at a declaration.  */
-  if (cp_parser_error_occurred (parser))
-    {
-      cp_parser_abort_tentative_parse (parser);
-      return NULL_TREE;
-    }
-  /* Parse the declarator.  */
-  declarator = cp_parser_declarator (parser, CP_PARSER_DECLARATOR_NAMED,
-				     /*ctor_dtor_or_conv_p=*/NULL,
-				     /*parenthesized_p=*/NULL,
-				     /*member_p=*/false);
-  /* Parse the attributes.  */
-  attributes = cp_parser_attributes_opt (parser);
-  /* The next token should be `:'. */
-  if (cp_lexer_next_token_is_not (parser->lexer, CPP_COLON))
-    cp_parser_simulate_error (parser);
-
-  /* Check if it is a range-based for */
-  if (!cp_parser_parse_definitely (parser))
-    return NULL_TREE;
+  tree stmt, range_expr;
 
-  cp_parser_require (parser, CPP_COLON, RT_COLON);
   if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE))
     {
       bool expr_non_constant_p;
@@ -8712,23 +8700,16 @@  cp_parser_range_for (cp_parser *parser)
   /* If in template, STMT is converted to a normal for-statements
      at instantiation. If not, it is done just ahead. */
   if (processing_template_decl)
-    stmt = begin_range_for_stmt ();
-  else
-    stmt = begin_for_stmt ();
-
-  /* Create the declaration. It must be after begin{,_range}_for_stmt(). */
-  range_decl = start_decl (declarator, &type_specifiers,
-			   /*initialized_p=*/SD_INITIALIZED,
-			   attributes, /*prefix_attributes=*/NULL_TREE,
-			   &pushed_scope);
-  /* No scope allowed here */
-  pop_scope (pushed_scope);
-
-  if (TREE_CODE (stmt) == RANGE_FOR_STMT)
-    finish_range_for_decl (stmt, range_decl, range_expr);
+    {
+      stmt = begin_range_for_stmt (scope, init);
+      finish_range_for_decl (stmt, range_decl, range_expr);
+    }
   else
-    /* Convert the range-based for loop into a normal for-statement. */
-    stmt = cp_convert_range_for (stmt, range_decl, range_expr);
+    {
+      stmt = begin_for_stmt (scope, init);
+      /* Convert the range-based for loop into a normal for-statement. */
+      stmt = cp_convert_range_for (stmt, range_decl, range_expr);
+    }
 
   return stmt;
 }
@@ -8955,12 +8936,7 @@  cp_parser_iteration_statement (cp_parser* parser)
 	/* Look for the `('.  */
 	cp_parser_require (parser, CPP_OPEN_PAREN, RT_OPEN_PAREN);
 
-	if (cxx_dialect == cxx0x)
-	  statement = cp_parser_range_for (parser);
-	else
-	  statement = NULL_TREE;
-	if (statement == NULL_TREE)
-	  statement = cp_parser_c_for (parser);
+	statement = cp_parser_for (parser);
 
 	/* Look for the `)'.  */
 	cp_parser_require (parser, CPP_CLOSE_PAREN, RT_CLOSE_PAREN);
@@ -8990,8 +8966,8 @@  cp_parser_iteration_statement (cp_parser* parser)
      expression-statement
      simple-declaration  */
 
-static void
-cp_parser_for_init_statement (cp_parser* parser)
+static kind_of_for_loop
+cp_parser_for_init_statement (cp_parser* parser, tree *decl)
 {
   /* If the next token is a `;', then we have an empty
      expression-statement.  Grammatically, this is also a
@@ -9001,19 +8977,44 @@  cp_parser_for_init_statement (cp_parser* parser)
      declaration.  */
   if (cp_lexer_next_token_is_not (parser->lexer, CPP_SEMICOLON))
     {
+      kind_of_for_loop res = FOR_LOOP_DECLARATION;
       /* We're going to speculatively look for a declaration, falling back
 	 to an expression, if necessary.  */
       cp_parser_parse_tentatively (parser);
       /* Parse the declaration.  */
       cp_parser_simple_declaration (parser,
-				    /*function_definition_allowed_p=*/false);
+				    /*function_definition_allowed_p=*/false,
+				    decl);
       /* If the tentative parse failed, then we shall need to look for an
 	 expression-statement.  */
+      if (cp_lexer_next_token_is (parser->lexer, CPP_COLON))
+	{
+	  if (cxx_dialect < cxx0x)
+	    {
+	      location_t loc = cp_lexer_peek_token (parser->lexer)->location;
+	      error_at (loc, "range-based-for loops are not allowed "
+			"in C++98 mode");
+	      cp_parser_skip_to_closing_parenthesis (parser,
+						     /*recovering=*/true,
+						     /*or_comma=*/false,
+						     /*consume_paren=*/false);
+	    }
+	  else
+	    {
+	      /* Consume the ':' */
+	      cp_lexer_consume_token (parser->lexer);
+	      res = FOR_LOOP_RANGE;
+	    }
+	}
+      else
+	/* The ';' is not consumed yet because we told
+	   cp_parser_simple_declaration not to.  */
+        cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
+
       if (cp_parser_parse_definitely (parser))
-	return;
+	return res;
     }
-
-  cp_parser_expression_statement (parser, NULL_TREE);
+  return FOR_LOOP_EXPRESSION;
 }
 
 /* Parse a jump-statement.
@@ -9500,7 +9501,7 @@  cp_parser_block_declaration (cp_parser *parser,
     cp_parser_static_assert (parser, /*member_p=*/false);
   /* Anything else must be a simple-declaration.  */
   else
-    cp_parser_simple_declaration (parser, !statement_p);
+    cp_parser_simple_declaration (parser, !statement_p, NULL);
 }
 
 /* Parse a simple-declaration.
@@ -9513,16 +9514,24 @@  cp_parser_block_declaration (cp_parser *parser,
      init-declarator-list , init-declarator
 
    If FUNCTION_DEFINITION_ALLOWED_P is TRUE, then we also recognize a
-   function-definition as a simple-declaration.  */
+   function-definition as a simple-declaration.
+
+   If JUST_ONE_DECLARATOR is not NULL, the pointed tree will be set to the 
+   parsed declaration iff it is a single declarator. Anyway, the trailing
+   ';' if present will not be checked nor consumed.  */
 
 static void
 cp_parser_simple_declaration (cp_parser* parser,
-			      bool function_definition_allowed_p)
+			      bool function_definition_allowed_p,
+			      tree *just_one_declarator)
 {
   cp_decl_specifier_seq decl_specifiers;
   int declares_class_or_enum;
   bool saw_declarator;
 
+  if (just_one_declarator)
+    *just_one_declarator = NULL_TREE;
+
   /* Defer access checks until we know what is being declared; the
      checks for names appearing in the decl-specifier-seq should be
      done as if we were in the scope of the thing being declared.  */
@@ -9546,6 +9555,9 @@  cp_parser_simple_declaration (cp_parser* parser,
   /* We no longer need to defer access checks.  */
   stop_deferring_access_checks ();
 
+  if (just_one_declarator && declares_class_or_enum != 0)
+    *just_one_declarator = error_mark_node;
+
   /* In a block scope, a valid declaration must always have a
      decl-specifier-seq.  By not trying to parse declarators, we can
      resolve the declaration/expression ambiguity more quickly.  */
@@ -9597,6 +9609,8 @@  cp_parser_simple_declaration (cp_parser* parser,
 	  token = cp_lexer_peek_token (parser->lexer);
 	  gcc_assert (token->type == CPP_COMMA);
 	  cp_lexer_consume_token (parser->lexer);
+	  if (just_one_declarator)
+	    *just_one_declarator = error_mark_node;
 	}
       else
 	saw_declarator = true;
@@ -9607,7 +9621,8 @@  cp_parser_simple_declaration (cp_parser* parser,
 					function_definition_allowed_p,
 					/*member_p=*/false,
 					declares_class_or_enum,
-					&function_definition_p);
+					&function_definition_p,
+					just_one_declarator);
       /* If an error occurred while parsing tentatively, exit quickly.
 	 (That usually happens when in the body of a function; each
 	 statement is treated as a declaration-statement until proven
@@ -9637,13 +9652,17 @@  cp_parser_simple_declaration (cp_parser* parser,
 	      return;
 	    }
 	}
+      if (just_one_declarator && *just_one_declarator == NULL_TREE)
+	*just_one_declarator = decl;
       /* The next token should be either a `,' or a `;'.  */
       token = cp_lexer_peek_token (parser->lexer);
       /* If it's a `,', there are more declarators to come.  */
       if (token->type == CPP_COMMA)
 	/* will be consumed next time around */;
       /* If it's a `;', we are done.  */
-      else if (token->type == CPP_SEMICOLON)
+      else if (token->type == CPP_SEMICOLON
+	       || (just_one_declarator 
+		   && *just_one_declarator != error_mark_node))
 	break;
       /* Anything else is an error.  */
       else
@@ -9681,7 +9700,8 @@  cp_parser_simple_declaration (cp_parser* parser,
     }
 
   /* Consume the `;'.  */
-  cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
+  if (!just_one_declarator)
+      cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
 
  done:
   pop_deferring_access_checks ();
@@ -14267,7 +14287,13 @@  cp_parser_asm_definition (cp_parser* parser)
    have been completely parsed.
 
    FUNCTION_DEFINITION_P may be NULL if FUNCTION_DEFINITION_ALLOWED_P
-   is FALSE.  */
+   is FALSE.
+   
+   If JUST_ONE_DECLARATOR is not NULL, the pointed tree will be set to the 
+   parsed declaration iff it is a single declarator without initialization.
+   The trailing ';' if present will not be checked nor consumed.
+   If returned, the declarator will be created with SD_INITIALIZED and 
+   will not call cp_finish_decl.  */
 
 static tree
 cp_parser_init_declarator (cp_parser* parser,
@@ -14276,7 +14302,8 @@  cp_parser_init_declarator (cp_parser* parser,
 			   bool function_definition_allowed_p,
 			   bool member_p,
 			   int declares_class_or_enum,
-			   bool* function_definition_p)
+			   bool* function_definition_p,
+			   tree* just_one_declarator)
 {
   cp_token *token = NULL, *asm_spec_start_token = NULL,
            *attributes_start_token = NULL;
@@ -14440,6 +14467,8 @@  cp_parser_init_declarator (cp_parser* parser,
     {
       is_initialized = SD_INITIALIZED;
       initialization_kind = token->type;
+      if (just_one_declarator)
+	*just_one_declarator = error_mark_node;
 
       if (token->type == CPP_EQ
 	  && function_declarator_p (declarator))
@@ -14453,16 +14482,23 @@  cp_parser_init_declarator (cp_parser* parser,
     }
   else
     {
+      is_initialized = SD_UNINITIALIZED;
+      initialization_kind = CPP_EOF;
       /* If the init-declarator isn't initialized and isn't followed by a
 	 `,' or `;', it's not a valid init-declarator.  */
       if (token->type != CPP_COMMA
 	  && token->type != CPP_SEMICOLON)
 	{
-	  cp_parser_error (parser, "expected initializer");
-	  return error_mark_node;
+	  if (just_one_declarator && *just_one_declarator != error_mark_node)
+	    {
+	      is_initialized = SD_INITIALIZED;
+	    }
+	  else
+	    {
+	      cp_parser_error (parser, "expected initializer");
+	      return error_mark_node;
+	    }
 	}
-      is_initialized = SD_UNINITIALIZED;
-      initialization_kind = CPP_EOF;
     }
 
   /* Because start_decl has side-effects, we should only call it if we
@@ -14538,7 +14574,7 @@  cp_parser_init_declarator (cp_parser* parser,
   initializer = NULL_TREE;
   is_direct_init = false;
   is_non_constant_init = true;
-  if (is_initialized)
+  if (is_initialized && initialization_kind != CPP_EOF)
     {
       if (function_declarator_p (declarator))
 	{
@@ -14606,7 +14642,8 @@  cp_parser_init_declarator (cp_parser* parser,
 
   /* Finish processing the declaration.  But, skip friend
      declarations.  */
-  if (!friend_p && decl && decl != error_mark_node)
+  if (!friend_p && decl && decl != error_mark_node
+      && (!is_initialized || initialization_kind != CPP_EOF))
     {
       cp_finish_decl (decl,
 		      initializer, !is_non_constant_init,
@@ -19833,7 +19870,8 @@  cp_parser_single_declaration (cp_parser* parser,
 				        /*function_definition_allowed_p=*/true,
 				        member_p,
 				        declares_class_or_enum,
-				        &function_definition_p);
+				        &function_definition_p,
+					NULL);
 
     /* 7.1.1-1 [dcl.stc]
 
diff --git gcc/cp/pt.c gcc/cp/pt.c
index 8a6d451..98e9453 100644
--- gcc/cp/pt.c
+++ gcc/cp/pt.c
@@ -11742,7 +11742,7 @@  tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
       }
 
     case FOR_STMT:
-      stmt = begin_for_stmt ();
+      stmt = begin_for_stmt (NULL_TREE, NULL_TREE);
       RECUR (FOR_INIT_STMT (t));
       finish_for_init_stmt (stmt);
       tmp = RECUR (FOR_COND (t));
@@ -11756,7 +11756,7 @@  tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
     case RANGE_FOR_STMT:
       {
         tree decl, expr;
-        stmt = begin_for_stmt ();
+        stmt = begin_for_stmt (NULL_TREE, NULL_TREE);
         decl = RANGE_FOR_DECL (t);
         decl = tsubst (decl, args, complain, in_decl);
         maybe_push_decl (decl);
diff --git gcc/cp/semantics.c gcc/cp/semantics.c
index 5926963..dff29c9 100644
--- gcc/cp/semantics.c
+++ gcc/cp/semantics.c
@@ -802,21 +802,44 @@  finish_return_stmt (tree expr)
   return r;
 }
 
-/* Begin a for-statement.  Returns a new FOR_STMT if appropriate.  */
+/* Begin the scope of a for-statement or a range-for-statement.
+   Both the returned trees are to be used in a call to
+   begin_for_stmt or begin_range_for_stmt.  */
 
 tree
-begin_for_stmt (void)
+begin_for_scope (tree *init)
+{
+  tree scope = NULL_TREE;
+  if (flag_new_for_scope > 0)
+    scope = do_pushlevel (sk_for);
+
+  if (processing_template_decl)
+    *init = push_stmt_list ();
+  else
+    *init = NULL_TREE;
+
+  return scope;
+}
+
+/* Begin a for-statement.  Returns a new FOR_STMT.
+   SCOPE and INIT should be the return of begin_for_scope, 
+   or both NULL_TREE  */
+
+tree
+begin_for_stmt (tree scope, tree init)
 {
   tree r;
 
   r = build_stmt (input_location, FOR_STMT, NULL_TREE, NULL_TREE,
 		  NULL_TREE, NULL_TREE);
 
-  if (flag_new_for_scope > 0)
-    TREE_CHAIN (r) = do_pushlevel (sk_for);
-
-  if (processing_template_decl)
-    FOR_INIT_STMT (r) = push_stmt_list ();
+  if (scope == NULL_TREE)
+    {
+      gcc_assert (!init);
+      scope = begin_for_scope (&init);
+    }
+  FOR_INIT_STMT (r) = init;
+  TREE_CHAIN (r) = scope;
 
   return r;
 }
@@ -900,18 +923,29 @@  finish_for_stmt (tree for_stmt)
 }
 
 /* Begin a range-for-statement.  Returns a new RANGE_FOR_STMT.
+   SCOPE and INIT should be the return of begin_for_scope, 
+   or both NULL_TREE  .
    To finish it call finish_for_stmt(). */
 
 tree
-begin_range_for_stmt (void)
+begin_range_for_stmt (tree scope, tree init)
 {
   tree r;
 
   r = build_stmt (input_location, RANGE_FOR_STMT,
 		  NULL_TREE, NULL_TREE, NULL_TREE);
 
-  if (flag_new_for_scope > 0)
-    TREE_CHAIN (r) = do_pushlevel (sk_for);
+  if (scope == NULL_TREE)
+    {
+      gcc_assert (!init);
+      scope = begin_for_scope (&init);
+    }
+
+  /* RANGE_FOR_STMTs do not use nor save the init tree, so we 
+     pop it now.  */
+  if (init)
+    pop_stmt_list (init);
+  TREE_CHAIN (r) = scope;
 
   return r;
 }
diff --git gcc/testsuite/g++.dg/cpp0x/range-for4.C gcc/testsuite/g++.dg/cpp0x/range-for4.C
index 96c0d90..afbcf14 100644
--- gcc/testsuite/g++.dg/cpp0x/range-for4.C
+++ gcc/testsuite/g++.dg/cpp0x/range-for4.C
@@ -3,8 +3,6 @@ 
 // { dg-do run }
 // { dg-options "-std=c++0x" }
 
-#include <cstdio>
-
 /* Preliminary declarations */
 namespace pre
 {
@@ -48,7 +46,6 @@  container run_me_just_once()
 }
 
 /* Template with dependent expression. */
-/* Template with dependent expression. */
 template<typename T> int test1(const T &r)
 {
   int t = 0;