Replace fixed size blocks with linked list

This adjustment enables compilation to use as much blocks as the
compilation  needs instead of allocating huge fixed-size array for
block structures to store, not only saves memory when compiling small
programs, but also prevents potential insufficient allocation issues
in the future work.

This improves significantly while compiling small programs. For example,
compiling "tests/hello.c" previously takes roughly 224.528 mb, while
this patch reduces to roughly 51.852 mb.

src/defs.h

@@ -21,7 +21,6 @@
 #define MAX_FIELDS 64
 #define MAX_FUNCS 512
 #define MAX_FUNC_TRIES 2160
-#define MAX_BLOCKS 2048
 #define MAX_TYPES 64
 #define MAX_IR_INSTR 50000
 #define MAX_BB_PRED 128
@@ -227,11 +226,16 @@ struct block {
     func_t *func;
     macro_t *macro;
     int locals_size;
-    int index;
+    struct block *next;
 };
 
 typedef struct block block_t;
 
+typedef struct {
+    block_t *head;
+    block_t *tail;
+} block_list_t;
+
 /* phase-1 IR definition */
 typedef struct {
     opcode_t op;

src/globals.c

@@ -7,8 +7,7 @@
 
 /* Global objects */
 
-block_t *BLOCKS;
-int blocks_idx = 0;
+block_list_t BLOCKS;
 
 macro_t *MACROS;
 int macros_idx = 0;
@@ -226,8 +225,16 @@ int find_label_offset(char name[])
 
 block_t *add_block(block_t *parent, func_t *func, macro_t *macro)
 {
-    block_t *blk = &BLOCKS[blocks_idx];
-    blk->index = blocks_idx++;
+    block_t *blk = malloc(sizeof(block_t));
+
+    if (!BLOCKS.head) {
+        BLOCKS.head = blk;
+        BLOCKS.tail = BLOCKS.head;
+    } else {
+        BLOCKS.tail->next = blk;
+        BLOCKS.tail = blk;
+    }
+
     blk->parent = parent;
     blk->func = func;
     blk->macro = macro;
@@ -394,7 +401,7 @@ var_t *find_local_var(char *token, block_t *block)
 
 var_t *find_global_var(char *token)
 {
-    block_t *block = &BLOCKS[0];
+    block_t *block = BLOCKS.head;
 
     for (int i = 0; i < block->next_local; i++) {
         if (!strcmp(block->locals[i].var_name, token))
@@ -587,7 +594,8 @@ void global_init()
 {
     elf_code_start = ELF_START + elf_header_len;
 
-    BLOCKS = malloc(MAX_BLOCKS * sizeof(block_t));
+    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));
@@ -613,7 +621,11 @@ void global_init()
 
 void global_release()
 {
-    free(BLOCKS);
+    while (BLOCKS.head) {
+        block_t *next = BLOCKS.head->next;
+        free(BLOCKS.head);
+        BLOCKS.head = next;
+    }
     free(MACROS);
     free(FUNCS);
     free(FUNC_TRIES);

src/parser.c

@@ -2153,7 +2153,7 @@ bool read_global_assignment(char *token)
 {
     ph1_ir_t *ph1_ir;
     var_t *vd;
-    block_t *parent = &BLOCKS[0];
+    block_t *parent = BLOCKS.head;
 
     /* global initialization must be constant */
     var_t *var = find_global_var(token);
@@ -3182,7 +3182,7 @@ void read_global_decl(block_t *block)
 void read_global_statement()
 {
     char token[MAX_ID_LEN];
-    block_t *block = &BLOCKS[0]; /* global block */
+    block_t *block = BLOCKS.head; /* global block */
 
     if (lex_accept(T_struct)) {
         int i = 0, size = 0;