Replace trie with general string-based-key hashmap

Previously, trie implementation is not consistent, mainly because of
using index to point the referencing func_t to FUNCS, additionally,
trie's advantage is that enables prefix lookup, but in shecc, it hasn't
been used in this way, furthur more, it takes 512 bytes per trie node,
while in this implementation, it 24 + W (W stands for key length
including NULL character) bytes per hashmap bucket node, which
significantly reduces memory usage.

This also allows for future refactoring of additional structures using
a hashmap implementation.

src/defs.h

@@ -20,7 +20,6 @@
 #define MAX_LOCALS 1500
 #define MAX_FIELDS 64
 #define MAX_FUNCS 512
-#define MAX_FUNC_TRIES 2160
 #define MAX_TYPES 64
 #define MAX_IR_INSTR 50000
 #define MAX_BB_PRED 128
@@ -305,10 +304,18 @@ typedef struct {
     int value;
 } constant_t;
 
+/* string-based hash map definitions */
+
+typedef struct hashmap_node {
+    char *key;
+    void *val;
+    struct hashmap_node *next;
+} hashmap_node_t;
+
 typedef struct {
-    int index;
-    int next[128];
-} trie_t;
+    int size;
+    hashmap_node_t **buckets;
+} hashmap_t;
 
 struct phi_operand {
     var_t *var;

src/globals.c

@@ -12,18 +12,13 @@ block_list_t BLOCKS;
 macro_t *MACROS;
 int macros_idx = 0;
 
-/* the first element is reserved for global scope */
-func_t *FUNCS;
-int funcs_idx = 1;
-
-/* FUNC_TRIES is used to improve the performance of the find_func function.
- * Instead of searching through all functions and comparing their names, we can
- * utilize the trie data structure to search for existing functions efficiently.
- * The index starts from 1 because the first trie node represents an empty input
- * string, and it is not possible to record a function with an empty name.
+/* FUNCS_MAP is used to integerate function storing and boost lookup
+ * performance, currently it uses FNV-1a hash function to hash function
+ * name. The bucket size defaults to MAX_FUNCS. Ideally, it should be a small
+ * number, but due to lack of rehashing implementation, to prevent collision,
+ * we have to initially create large amount of buckets.
  */
-trie_t *FUNC_TRIES;
-int func_tries_idx = 1;
+hashmap_t *FUNCS_MAP;
 
 type_t *TYPES;
 int types_idx = 0;
@@ -72,72 +67,144 @@ char *elf_strtab;
 char *elf_section;
 
 /**
- * insert_trie() - Inserts a new element into the trie structure.
- * @trie: A pointer to the trie where the name will be inserted.
- * @name: The name to be inserted into the trie.
- * @funcs_index: The index of the pointer to the func_t. The index is recorded
- *     in a 1-indexed format. Because the first element of 'FUNCS' has been
- *     reserved, there is no need to shift it.
- * Return: The index of the pointer to the func_t.
+ * hash_index() - hashses a string with FNV-1a hash function
+ * and converts into usable hashmap index. The range of returned
+ * hashmap index is ranged from "(0 ~ 2,147,483,647) mod size" due to
+ * lack of unsigned integer implementation.
+ * @size: The size of map. Must not be negative or 0.
+ * @key: The key string. May be NULL.
  *
- * If the function has been inserted, the return value is the index of the
- * function in FUNCS. Otherwise, the return value is the value of the parameter
- * @funcs_index.
+ * @returns: The usable hashmap index.
  */
-int insert_trie(trie_t *trie, char *name, int funcs_index)
-{
-    char first_char;
-    int fc;
-
-    while (1) {
-        first_char = *name;
-        fc = first_char;
-        if (!fc) {
-            if (!trie->index)
-                trie->index = funcs_index;
-            return trie->index;
-        }
-        if (!trie->next[fc]) {
-            /* FIXME: The func_tries_idx variable may exceed the maximum number,
-             * which can lead to a segmentation fault. This issue is affected by
-             * the number of functions and the length of their names. The proper
-             * way to handle this is to dynamically allocate a new element.
-             */
-            trie->next[fc] = func_tries_idx++;
-            for (int i = 0; i < 128; i++)
-                FUNC_TRIES[trie->next[fc]].next[i] = 0;
-            FUNC_TRIES[trie->next[fc]].index = 0;
-        }
-        trie = &FUNC_TRIES[trie->next[fc]];
-        name++;
+int hash_index(int size, char *key)
+{
+    int hash = 0x811c9dc5, mask;
+
+    for (; *key; key++) {
+        hash ^= *key;
+        hash *= 0x01000193;
+    }
+
+    mask = hash >> 31;
+    return ((hash ^ mask) - mask) % size;
+}
+
+/**
+ * hashmap_create() - creates a hashmap on heap.
+ * @size: The initial bucket size of hashmap. Must not be 0.
+ *
+ * @returns: The pointer of created hashmap.
+ */
+hashmap_t *hashmap_create(int size)
+{
+    hashmap_t *map = malloc(sizeof(hashmap_t));
+    map->size = size;
+    map->buckets = malloc(size * sizeof(hashmap_node_t *));
+
+    for (int i = 0; i < map->size; i++)
+        map->buckets[i] = 0;
+
+    return map;
+}
+
+/**
+ * hashmap_node_new() - creates a hashmap node on heap.
+ * @key: The key of node. Must not be NULL.
+ * @val: The value of node. Could be NULL.
+ *
+ * @returns: The pointer of created node.
+ */
+hashmap_node_t *hashmap_node_new(char *key, void *val)
+{
+    int len = strlen(key);
+    hashmap_node_t *node = malloc(sizeof(hashmap_node_t));
+    node->key = calloc(len + 1, sizeof(char));
+    strcpy(node->key, key);
+    node->val = val;
+    node->next = NULL;
+    return node;
+}
+
+/**
+ * hashmap_put() - puts a key-value pair into given hashmap.
+ * If key already contains a value, then replace it with new
+ * value, the old value will be freed.
+ * @map: The hashmap to be put into. Must not be NULL.
+ * @key: The key string. May be NULL.
+ * @val: The value pointer. May be NULL. This value's lifetime
+ * is held by hashmap.
+ */
+void hashmap_put(hashmap_t *map, char *key, void *val)
+{
+    int index = hash_index(map->size, key);
+    hashmap_node_t *cur = map->buckets[index];
+
+    if (!cur) {
+        map->buckets[index] = hashmap_node_new(key, val);
+    } else {
+        while (cur->next)
+            cur = cur->next;
+        cur->next = hashmap_node_new(key, val);
     }
+
+    /* TODO: Rehash if size exceeds size * load factor */
 }
 
 /**
- * find_trie() - search the index of the function name in the trie
- * @trie: A pointer to the trie where the name will be searched.
- * @name: The name to be searched.
+ * hashmap_get() - gets value from hashmap from given key.
+ * @map: The hashmap to be looked up. Must no be NULL.
+ * @key: The key string. May be NULL.
  *
- * Return: The index of the pointer to the func_t.
+ * @returns: The look up result, if the key-value pair entry
+ * exists, then returns its value's address, NULL otherwise.
+ */
+void *hashmap_get(hashmap_t *map, char *key)
+{
+    int index = hash_index(map->size, key);
+
+    for (hashmap_node_t *cur = map->buckets[index]; cur; cur = cur->next)
+        if (!strcmp(cur->key, key))
+            return cur->val;
+
+    return NULL;
+}
+
+/**
+ * hashmap_contains() - checks if the key-value pair entry exists
+ * from given key.
+ * @map: The hashmap to be looked up. Must no be NULL.
+ * @key: The key string. May be NULL.
  *
- * 0 - the name not found.
- * otherwise - the index of the founded index in the trie array.
+ * @returns: The look up result, if the key-value pair entry
+ * exists, then returns true, false otherwise.
+ */
+bool hashmap_contains(hashmap_t *map, char *key)
+{
+    return hashmap_get(map, key) != NULL;
+}
+
+/**
+ * hashmap_free() - frees the hashmap, this also frees key-value pair
+ * entry's value.
+ * @map: The hashmap to be looked up. Must no be NULL.
  */
-int find_trie(trie_t *trie, char *name)
-{
-    char first_char;
-    int fc;
-
-    while (1) {
-        first_char = *name;
-        fc = first_char;
-        if (!fc)
-            return trie->index;
-        if (!trie->next[fc])
-            return 0;
-        trie = &FUNC_TRIES[trie->next[fc]];
-        name++;
+void hashmap_free(hashmap_t *map)
+{
+    for (int i = 0; i < map->size; i++) {
+        for (hashmap_node_t *cur = map->buckets[i], *next; cur;
+             cur = cur->next) {
+            next = cur->next;
+            free(cur->key);
+            free(cur->val);
+            /* FIXME: Remove this if-clause will cause double free error */
+            if (cur != map->buckets[0])
+                free(cur);
+            cur = next;
+        }
     }
+
+    free(map->buckets);
+    free(map);
 }
 
 /* options */
@@ -318,12 +385,14 @@ int find_macro_param_src_idx(char *name, block_t *parent)
 func_t *add_func(char *name)
 {
     func_t *fn;
-    int index = insert_trie(FUNC_TRIES, name, funcs_idx);
-    if (index == funcs_idx) {
-        fn = &FUNCS[funcs_idx++];
+    if (hashmap_contains(FUNCS_MAP, name)) {
+        fn = hashmap_get(FUNCS_MAP, name);
+    } else {
+        fn = malloc(sizeof(func_t));
+        hashmap_put(FUNCS_MAP, name, fn);
         strcpy(fn->return_def.var_name, name);
     }
-    fn = &FUNCS[index];
+
     fn->stack_size = 4; /* starting point of stack */
     return fn;
 }
@@ -358,10 +427,7 @@ constant_t *find_constant(char alias[])
 
 func_t *find_func(char func_name[])
 {
-    int index = find_trie(FUNC_TRIES, func_name);
-    if (index)
-        return &FUNCS[index];
-    return NULL;
+    return hashmap_get(FUNCS_MAP, func_name);
 }
 
 var_t *find_member(char token[], type_t *type)
@@ -597,8 +663,7 @@ void global_init()
     BLOCKS.head = NULL;
     BLOCKS.tail = NULL;
     MACROS = malloc(MAX_ALIASES * sizeof(macro_t));
-    FUNCS = malloc(MAX_FUNCS * sizeof(func_t));
-    FUNC_TRIES = malloc(MAX_FUNC_TRIES * sizeof(trie_t));
+    FUNCS_MAP = hashmap_create(MAX_FUNCS);
     TYPES = malloc(MAX_TYPES * sizeof(type_t));
     GLOBAL_IR = malloc(MAX_GLOBAL_IR * sizeof(ph1_ir_t));
     PH1_IR = malloc(MAX_IR_INSTR * sizeof(ph1_ir_t));
@@ -616,7 +681,8 @@ void global_init()
     elf_section = malloc(MAX_SECTION);
 
     /* set starting point of global stack manually */
-    FUNCS[0].stack_size = 4;
+    func_t *global_func = add_func("");
+    global_func->stack_size = 4;
 }
 
 void global_release()
@@ -627,8 +693,7 @@ void global_release()
         BLOCKS.head = next;
     }
     free(MACROS);
-    free(FUNCS);
-    free(FUNC_TRIES);
+    hashmap_free(FUNCS_MAP);
     free(TYPES);
     free(GLOBAL_IR);
     free(PH1_IR);