Convert the recursive code for freeing AST into an interative one

Profiling showed that a lot of time is spent in freeing up the tree -
making it non-recursive should speed it up

Author: abhinav-upadhyay

parser.c

@@ -409,6 +409,35 @@ regex_free(regex_t *regex)
     free(regex);
 }
 
+void
+free_expression2(expression_node_t *exp)
+{
+    cm_stack *stack = cm_stack_init(64);
+    cm_stack_push(stack, exp);
+    while (stack->length > 0) {
+        expression_node_t *e = (expression_node_t *) cm_stack_pop(stack);
+        if (e->type == CHAR_LITERAL || e->type == CHAR_LITERAL) {
+            free(e);
+            continue;
+        }
+        if (e->type == INFIX_EXPRESSION) {
+            infix_expression_t *infix = (infix_expression_t *) e;
+            cm_stack_push(stack, infix->left);
+            cm_stack_push(stack, infix->right);
+            free(e);
+            continue;
+        }
+        if (e->type == POSTFIX_EXPRESSION) {
+            postfix_expression_t *postfix = (postfix_expression_t *) e;
+            cm_stack_push(stack, postfix->left);
+            free(e);
+            continue;
+        }
+        free(e);
+    }
+    cm_stack_free(stack);
+}
+
 void
 free_expression(expression_node_t *exp)
 {

re_utils.c

@@ -78,8 +78,8 @@ cm_list_free(cm_list *list, void (*free_data) (void *))
     while (list_node != NULL) {
         if (free_data)
             free_data(list_node->data);
-        else
-            free(list_node->data);
+        // else
+            // free(list_node->data);
         temp_node = list_node->next;
         free(list_node);
         list_node = temp_node;
@@ -466,3 +466,29 @@ pointer_equals(void *key1, void*key2)
 {
     return key1 == key2;
 }
+
+void
+cm_stack_push(cm_stack *stack, void *v)
+{
+    cm_array_list *l = (cm_array_list *) stack;
+    cm_array_list_add(l, v);
+}
+
+void *
+cm_stack_pop(cm_stack *stack)
+{
+    stack->length--;
+    return stack->array[stack->length];
+}
+
+cm_stack *
+cm_stack_init(size_t init_size)
+{
+    return (cm_stack *) cm_array_list_init(init_size, NULL);
+}
+
+void
+cm_stack_free(cm_stack *stack)
+{
+    cm_array_list_free((cm_array_list *) stack);
+}

re_utils.h

@@ -69,6 +69,8 @@ typedef struct cm_hash_table {
     void (*free_value) (void *);
 } cm_hash_table;
 
+typedef cm_array_list cm_stack;
+
 
 cm_list *cm_list_init(void);
 int cm_list_add(cm_list *, void *);
@@ -83,6 +85,10 @@ void *cm_array_list_last(cm_array_list *);
 void *cm_array_list_first(cm_array_list *);
 void cm_array_list_remove(cm_array_list *, size_t);
 void cm_array_list_free(cm_array_list *);
+void * cm_stack_pop(cm_stack *);
+void cm_stack_push(cm_stack *, void *);
+cm_stack *cm_stack_init(size_t);
+void cm_stack_free(cm_stack *);
 char *cm_array_string_list_join(cm_array_list *, const char *);
 cm_array_list *cm_array_list_copy(cm_array_list *, void * (*copy_func) (void *));