Merge pull request sysprog21#184 from ChAoSUnItY/feat/arena

Implement arena allocator to reduce allocation

Author: jserv

lib/c.c

@@ -629,12 +629,27 @@ void *malloc(int size)
 
 void *calloc(int n, int size)
 {
-    char *p = malloc(n * size);
+    int total = n * size;
+    char *p = malloc(total);
 
     if (!p)
         return NULL;
-    for (int i = 0; i < n * size; i++)
-        p[i] = 0;
+
+    /* TODO: Replace the byte buffer clearing algorithm with memset once
+     * implemented.
+     */
+
+    /* Currently malloc uses mmap(2) to request allocation, which guarantees
+     * memory to be page-aligned
+     */
+    int *pi = p, num_words = total >> 2, offset = num_words << 2;
+
+    for (int i = 0; i < num_words; i++)
+        pi[i] = 0;
+
+    while (offset < total)
+        p[offset++] = 0;
+
     return p;
 }
 

src/arm-codegen.c

@@ -156,8 +156,7 @@ void cfg_flatten()
 
             for (ph2_ir_t *insn = bb->ph2_ir_list.head; insn;
                  insn = insn->next) {
-                flatten_ir = add_ph2_ir(OP_generic);
-                memcpy(flatten_ir, insn, sizeof(ph2_ir_t));
+                flatten_ir = add_existed_ph2_ir(insn);
 
                 if (insn->op == OP_return) {
                     /* restore sp */
@@ -470,7 +469,7 @@ void code_generate()
     emit(__b(__AL, MAIN_BB->elf_offset - elf_code_idx));
 
     for (int i = 0; i < ph2_ir_idx; i++) {
-        ph2_ir = &PH2_IR[i];
+        ph2_ir = PH2_IR_FLATTEN[i];
         emit_ph2_ir(ph2_ir);
     }
 }

src/defs.h

@@ -41,6 +41,10 @@
 #define MAX_OPERAND_STACK_SIZE 32
 #define MAX_ANALYSIS_STACK_SIZE 750
 
+/* Default capacities for common data structures */
+/* Default arena size is initialized with 256 KiB */
+#define DEFAULT_ARENA_SIZE 262144
+
 #define ELF_START 0x10000
 #define PTR_SIZE 4
 
@@ -62,6 +66,18 @@
 #define HOST_PTR_SIZE __SIZEOF_POINTER__
 #endif
 
+/* Common data structures */
+typedef struct arena_block {
+    char *memory;
+    int capacity;
+    int offset;
+    struct arena_block *next;
+} arena_block_t;
+
+typedef struct {
+    arena_block_t *head;
+} arena_t;
+
 /* builtin types */
 typedef enum {
     TYPE_void = 0,

src/globals.c

@@ -32,7 +32,12 @@ int global_ir_idx = 0;
 ph1_ir_t *PH1_IR;
 int ph1_ir_idx = 0;
 
-ph2_ir_t *PH2_IR;
+arena_t *INSN_ARENA;
+
+/* BB_ARENA is responsible for basic_block_t / ph2_ir_t allocation */
+arena_t *BB_ARENA;
+
+ph2_ir_t **PH2_IR_FLATTEN;
 int ph2_ir_idx = 0;
 
 label_lut_t *LABEL_LUT;
@@ -69,6 +74,121 @@ char *elf_symtab;
 char *elf_strtab;
 char *elf_section;
 
+/**
+ * arena_block_create() - creates a new arena block with given capacity.
+ * The created arena block is guaranteed to be zero-initialized.
+ * @capacity: The capacity of the arena block. Must be positive.
+ *
+ * Return: The pointer of created arena block. NULL if failed to allocate.
+ */
+arena_block_t *arena_block_create(int capacity)
+{
+    arena_block_t *block = malloc(sizeof(arena_block_t));
+
+    if (!block) {
+        printf("Failed to allocate memory for arena block\n");
+        exit(1);
+    }
+
+    block->memory = calloc(capacity, sizeof(char));
+
+    if (!block->memory) {
+        printf("Failed to allocate memory for arena block\n");
+        free(block);
+        exit(1);
+    }
+
+    block->capacity = capacity;
+    block->offset = 0;
+    block->next = NULL;
+    return block;
+}
+
+/**
+ * arena_init() - initializes the given arena with initial capacity.
+ * @initial_capacity: The initial capacity of the arena. Must be positive.
+ *
+ * Return: The pointer of initialized arena.
+ */
+arena_t *arena_init(int initial_capacity)
+{
+    arena_t *arena = malloc(sizeof(arena_t));
+    arena->head = arena_block_create(initial_capacity);
+    return arena;
+}
+
+/**
+ * arena_alloc() - allocates memory from the given arena with given size.
+ * The arena may create a new arena block if no space is available.
+ * @arena: The arena to allocate memory from. Must not be NULL.
+ * @size: The size of memory to allocate. Must be positive.
+ *
+ * Return: The pointer of allocated memory. NULL if new arena block is failed to
+ * allocate.
+ */
+void *arena_alloc(arena_t *arena, int size)
+{
+    char *ptr;
+    arena_block_t *block = arena->head;
+
+    while (block) {
+        if (block->offset + size <= block->capacity) {
+            ptr = block->memory + block->offset;
+            block->offset += size;
+            return ptr;
+        }
+        if (!block->next)
+            break;
+        block = block->next;
+    }
+
+    /* If no space is available, create a new block
+     * Allocate at least 256 KiB or the requested size
+     */
+    int new_capacity = size > DEFAULT_ARENA_SIZE ? size : DEFAULT_ARENA_SIZE;
+    arena_block_t *new_block = arena_block_create(new_capacity);
+
+    if (!new_block)
+        return NULL;
+
+    block->next = new_block;
+    ptr = new_block->memory + new_block->offset;
+    new_block->offset += size;
+    return ptr;
+}
+
+/**
+ * arena_reset() - resets the given arena by resetting all blocks' offset to 0.
+ * @arena: The arena to reset. Must not be NULL.
+ */
+void arena_reset(arena_t *arena)
+{
+    arena_block_t *block = arena->head;
+
+    while (block) {
+        block->offset = 0;
+        block = block->next;
+    }
+}
+
+/**
+ * arena_free() - frees the given arena and all its blocks.
+ * @arena: The arena to free. Must not be NULL.
+ */
+void arena_free(arena_t *arena)
+{
+    arena_block_t *block = arena->head, *next;
+
+    while (block) {
+        next = block->next;
+        free(block->memory);
+        free(block);
+        block = next;
+    }
+
+    free(arena);
+}
+
 /**
  * hashmap_hash_index() - hashses a string with FNV-1a hash function
  * and converts into usable hashmap index. The range of returned
@@ -312,11 +432,17 @@ ph1_ir_t *add_ph1_ir(opcode_t op)
     return ph1_ir;
 }
 
+ph2_ir_t *add_existed_ph2_ir(ph2_ir_t *ph2_ir)
+{
+    PH2_IR_FLATTEN[ph2_ir_idx++] = ph2_ir;
+    return ph2_ir;
+}
+
 ph2_ir_t *add_ph2_ir(opcode_t op)
 {
-    ph2_ir_t *ph2_ir = &PH2_IR[ph2_ir_idx++];
+    ph2_ir_t *ph2_ir = arena_alloc(BB_ARENA, sizeof(ph2_ir_t));
     ph2_ir->op = op;
-    return ph2_ir;
+    return add_existed_ph2_ir(ph2_ir);
 }
 
 void set_var_liveout(var_t *var, int end)
@@ -579,7 +705,7 @@ fn_t *add_fn()
 /* Create a basic block and set the scope of variables to 'parent' block */
 basic_block_t *bb_create(block_t *parent)
 {
-    basic_block_t *bb = calloc(1, sizeof(basic_block_t));
+    basic_block_t *bb = arena_alloc(BB_ARENA, sizeof(basic_block_t));
 
     for (int i = 0; i < MAX_BB_PRED; i++) {
         bb->prev[i].bb = NULL;
@@ -691,7 +817,7 @@ void add_insn(block_t *block,
 
     bb->scope = block;
 
-    insn_t *n = calloc(1, sizeof(insn_t));
+    insn_t *n = arena_alloc(INSN_ARENA, sizeof(insn_t));
     n->opcode = op;
     n->rd = rd;
     n->rs1 = rs1;
@@ -725,7 +851,9 @@ void global_init()
     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));
-    PH2_IR = malloc(MAX_IR_INSTR * sizeof(ph2_ir_t));
+    INSN_ARENA = arena_init(DEFAULT_ARENA_SIZE);
+    BB_ARENA = arena_init(DEFAULT_ARENA_SIZE);
+    PH2_IR_FLATTEN = malloc(MAX_IR_INSTR * sizeof(ph2_ir_t *));
     LABEL_LUT = malloc(MAX_LABEL * sizeof(label_lut_t));
     SOURCE = malloc(MAX_SOURCE);
     ALIASES = malloc(MAX_ALIASES * sizeof(alias_t));
@@ -755,7 +883,9 @@ void global_release()
     free(TYPES);
     free(GLOBAL_IR);
     free(PH1_IR);
-    free(PH2_IR);
+    arena_free(INSN_ARENA);
+    arena_free(BB_ARENA);
+    free(PH2_IR_FLATTEN);
     free(LABEL_LUT);
     free(SOURCE);
     free(ALIASES);

src/main.c

@@ -115,7 +115,6 @@ int main(int argc, char *argv[])
     elf_generate(out);
 
     /* release allocated objects */
-    ssa_release();
     global_release();
 
     exit(0);

src/reg-alloc.c

@@ -49,7 +49,7 @@ void refresh(basic_block_t *bb, insn_t *insn)
 
 ph2_ir_t *bb_add_ph2_ir(basic_block_t *bb, opcode_t op)
 {
-    ph2_ir_t *n = calloc(1, sizeof(ph2_ir_t));
+    ph2_ir_t *n = arena_alloc(BB_ARENA, sizeof(ph2_ir_t));
     n->op = op;
 
     if (!bb->ph2_ir_list.head)
@@ -640,7 +640,7 @@ void reg_alloc()
 void dump_ph2_ir()
 {
     for (int i = 0; i < ph2_ir_idx; i++) {
-        ph2_ir_t *ph2_ir = &PH2_IR[i];
+        ph2_ir_t *ph2_ir = PH2_IR_FLATTEN[i];
 
         int rd = ph2_ir->dest + 48;
         int rs1 = ph2_ir->src0 + 48;

src/riscv-codegen.c

@@ -128,8 +128,7 @@ void cfg_flatten()
 
             for (ph2_ir_t *insn = bb->ph2_ir_list.head; insn;
                  insn = insn->next) {
-                flatten_ir = add_ph2_ir(OP_generic);
-                memcpy(flatten_ir, insn, sizeof(ph2_ir_t));
+                flatten_ir = add_existed_ph2_ir(insn);
 
                 if (insn->op == OP_return) {
                     /* restore sp */
@@ -446,7 +445,7 @@ void code_generate()
     emit(__jal(__zero, MAIN_BB->elf_offset - elf_code_idx));
 
     for (int i = 0; i < ph2_ir_idx; i++) {
-        ph2_ir = &PH2_IR[i];
+        ph2_ir = PH2_IR_FLATTEN[i];
         emit_ph2_ir(ph2_ir);
     }
 }

src/ssa.c

@@ -588,7 +588,7 @@ bool insert_phi_insn(basic_block_t *bb, var_t *var)
         return false;
 
     insn_t *head = bb->insn_list.head;
-    insn_t *n = calloc(1, sizeof(insn_t));
+    insn_t *n = arena_alloc(INSN_ARENA, sizeof(insn_t));
     n->opcode = OP_phi;
     n->rd = var;
     n->rs1 = var;
@@ -810,7 +810,7 @@ void solve_phi_params()
 
 void append_unwound_phi_insn(basic_block_t *bb, var_t *dest, var_t *rs)
 {
-    insn_t *n = calloc(1, sizeof(insn_t));
+    insn_t *n = arena_alloc(INSN_ARENA, sizeof(insn_t));
     n->opcode = OP_unwound_phi;
     n->rd = dest;
     n->rs1 = rs;
@@ -1770,52 +1770,3 @@ void liveness_analysis()
         } while (changed);
     }
 }
-
-void bb_release(fn_t *fn, basic_block_t *bb)
-{
-    UNUSED(fn);
-
-    insn_t *insn = bb->insn_list.head;
-    insn_t *next_insn;
-    while (insn) {
-        next_insn = insn->next;
-        free(insn);
-        insn = next_insn;
-    }
-
-    /* disconnect all predecessors */
-    for (int i = 0; i < MAX_BB_PRED; i++) {
-        if (!bb->prev[i].bb)
-            continue;
-        switch (bb->prev[i].type) {
-        case NEXT:
-            bb->prev[i].bb->next = NULL;
-            break;
-        case THEN:
-            bb->prev[i].bb->then_ = NULL;
-            break;
-        case ELSE:
-            bb->prev[i].bb->else_ = NULL;
-            break;
-        default:
-            abort();
-        }
-
-        bb->prev[i].bb = NULL;
-    }
-    free(bb);
-}
-
-void ssa_release()
-{
-    bb_traversal_args_t *args = calloc(1, sizeof(bb_traversal_args_t));
-    for (fn_t *fn = FUNC_LIST.head; fn; fn = fn->next) {
-        args->fn = fn;
-        args->bb = fn->bbs;
-
-        fn->visited++;
-        args->postorder_cb = bb_release;
-        bb_forward_traversal(args);
-    }
-    free(args);
-}