Eliminate some recursion from children of _expand_token_list

Previously, both _expand_node and _expand_function would always make
mutually recursive calls into _expand_token_list. This was unnecessary
since these functions can simply return unexpanded results, after which
the outer iteration will next attempt expansion of the results.

The only trick in doing this is to arrange so that the active list is
popped at the appropriate time. To do this, we add a new token_node_t
marker to the active stack. When pushing onto the active list, we set
marker to last->next, and when the marker is seen by the token list
iteration, we pop from the active stack.

glcpp-parse.y

@@ -52,12 +52,6 @@ _string_list_append_item (string_list_t *list, const char *str);
 static void
 _string_list_append_list (string_list_t *list, string_list_t *tail);
 
-static void
-_string_list_push (string_list_t *list, const char *str);
-
-static void
-_string_list_pop (string_list_t *list);
-
 static int
 _string_list_contains (string_list_t *list, const char *member, int *index);
 
@@ -96,6 +90,20 @@ _token_list_append (token_list_t *list, token_t *token);
 static void
 _token_list_append_list (token_list_t *list, token_list_t *tail);
 
+static int
+_token_list_length (token_list_t *list);
+
+static active_list_t *
+_active_list_push (active_list_t *list,
+		   const char *identifier,
+		   token_node_t *marker);
+
+static active_list_t *
+_active_list_pop (active_list_t *list);
+
+int
+_active_list_contains (active_list_t *list, const char *identifier);
+
 static void
 _glcpp_parser_evaluate_defined (glcpp_parser_t *parser,
 				token_list_t *list);
@@ -468,42 +476,6 @@ _string_list_append_item (string_list_t *list, const char *str)
 	list->tail = node;
 }
 
-void
-_string_list_push (string_list_t *list, const char *str)
-{
-	string_node_t *node;
-
-	node = xtalloc (list, string_node_t);
-	node->str = xtalloc_strdup (node, str);
-	node->next = list->head;
-
-	if (list->tail == NULL) {
-		list->tail = node;
-	}
-	list->head = node;
-}
-
-void
-_string_list_pop (string_list_t *list)
-{
-	string_node_t *node;
-
-	node = list->head;
-
-	if (node == NULL) {
-		fprintf (stderr, "Internal error: _string_list_pop called on an empty list.\n");
-		exit (1);
-	}
-
-	list->head = node->next;
-	if (list->tail == node) {
-		assert (node->next == NULL);
-		list->tail = NULL;
-	}
-
-	talloc_free (node);
-}
-
 int
 _string_list_contains (string_list_t *list, const char *member, int *index)
 {
@@ -716,6 +688,21 @@ _token_list_trim_trailing_space (token_list_t *list)
 	}
 }
 
+static int
+_token_list_length (token_list_t *list)
+{
+	int length = 0;
+	token_node_t *node;
+
+	if (list == NULL)
+		return 0;
+
+	for (node = list->head; node; node = node->next)
+		length++;
+
+	return length;
+}
+
 static void
 _token_print (token_t *token)
 {
@@ -880,7 +867,7 @@ glcpp_parser_create (void)
 	glcpp_lex_init_extra (parser, &parser->scanner);
 	parser->defines = hash_table_ctor (32, hash_table_string_hash,
 					   hash_table_string_compare);
-	parser->active = _string_list_create (parser);
+	parser->active = NULL;
 	parser->lexing_if = 0;
 	parser->space_tokens = 1;
 	parser->newline_as_space = 0;
@@ -1176,10 +1163,6 @@ _glcpp_parser_expand_function (glcpp_parser_t *parser,
 
 	substituted->non_space_tail = substituted->tail;
 
-	_string_list_push (parser->active, identifier);
-	_glcpp_parser_expand_token_list (parser, substituted);
-	_string_list_pop (parser->active);
-
 	return substituted;
 }
 
@@ -1206,7 +1189,6 @@ _glcpp_parser_expand_node (glcpp_parser_t *parser,
 	token_t *token = node->token;
 	const char *identifier;
 	macro_t *macro;
-	token_list_t *expansion;
 
 	/* We only expand identifiers */
 	if (token->type != IDENTIFIER) {
@@ -1231,7 +1213,7 @@ _glcpp_parser_expand_node (glcpp_parser_t *parser,
 
 	/* Finally, don't expand this macro if we're already actively
 	 * expanding it, (to avoid infinite recursion). */
-	if (_string_list_contains (parser->active, identifier, NULL)) {
+	if (_active_list_contains (parser->active, identifier)) {
 		/* We change the token type here from IDENTIFIER to
 		 * OTHER to prevent any future expansion of this
 		 * unexpanded token. */
@@ -1254,18 +1236,63 @@ _glcpp_parser_expand_node (glcpp_parser_t *parser,
 		if (macro->replacements == NULL)
 			return _token_list_create (parser);
 
-		expansion = _token_list_copy (parser, macro->replacements);
-
-		_string_list_push (parser->active, identifier);
-		_glcpp_parser_expand_token_list (parser, expansion);
-		_string_list_pop (parser->active);
-
-		return expansion;
+		return _token_list_copy (parser, macro->replacements);
 	}
 
 	return _glcpp_parser_expand_function (parser, node, last);
 }
 
+/* Push a new identifier onto the active list, returning the new list.
+ *
+ * Here, 'marker' is the token node that appears in the list after the
+ * expansion of 'identifier'. That is, when the list iterator begins
+ * examinging 'marker', then it is time to pop this node from the
+ * active stack.
+ */
+active_list_t *
+_active_list_push (active_list_t *list,
+		   const char *identifier,
+		   token_node_t *marker)
+{
+	active_list_t *node;
+
+	node = xtalloc (list, active_list_t);
+	node->identifier = xtalloc_strdup (node, identifier);
+	node->marker = marker;
+	node->next = list;
+
+	return node;
+}
+
+active_list_t *
+_active_list_pop (active_list_t *list)
+{
+	active_list_t *node = list;
+
+	if (node == NULL)
+		return NULL;
+
+	node = list->next;
+	talloc_free (list);
+
+	return node;
+}
+
+int
+_active_list_contains (active_list_t *list, const char *identifier)
+{
+	active_list_t *node;
+
+	if (list == NULL)
+		return 0;
+
+	for (node = list; node; node = node->next)
+		if (strcmp (node->identifier, identifier) == 0)
+			return 1;
+
+	return 0;
+}
+
 /* Walk over the token list replacing nodes with their expansion.
  * Whenever nodes are expanded the walking will walk over the new
  * nodes, continuing to expand as necessary. The results are placed in
@@ -1288,10 +1315,27 @@ _glcpp_parser_expand_token_list (glcpp_parser_t *parser,
 	node = list->head;
 
 	while (node) {
+
+		while (parser->active && parser->active->marker == node)
+			parser->active = _active_list_pop (parser->active);
+
 		/* Find the expansion for node, which will replace all
 		 * nodes from node to last, inclusive. */
 		expansion = _glcpp_parser_expand_node (parser, node, &last);
 		if (expansion) {
+			token_node_t *n;
+
+			for (n = node; n != last->next; n = n->next)
+				while (parser->active &&
+				       parser->active->marker == n)
+				{
+					parser->active = _active_list_pop (parser->active);
+				}
+
+			parser->active = _active_list_push (parser->active,
+							    node->token->value.str,
+							    last->next);
+			
 			/* Splice expansion into list, supporting a
 			 * simple deletion if the expansion is
 			 * empty. */
@@ -1317,6 +1361,9 @@ _glcpp_parser_expand_token_list (glcpp_parser_t *parser,
 		node = node_prev ? node_prev->next : list->head;
 	}
 
+	while (parser->active)
+		parser->active = _active_list_pop (parser->active);
+
 	list->non_space_tail = list->tail;
 }
 

glcpp.h

@@ -123,10 +123,16 @@ typedef struct skip_node {
 	struct skip_node *next;
 } skip_node_t;
 
+typedef struct active_list {
+	const char *identifier;
+	token_node_t *marker;
+	struct active_list *next;
+} active_list_t;
+
 struct glcpp_parser {
 	yyscan_t scanner;
 	struct hash_table *defines;
-	string_list_t *active;
+	active_list_t *active;
 	int lexing_if;
 	int space_tokens;
 	int newline_as_space;