Improve efficiency of branch history table

src/decode.h

@@ -254,9 +254,10 @@ typedef struct {
 
 #define HISTORY_SIZE 16
 typedef struct {
-    uint32_t PC;
-    struct rv_insn *branch_target;
-} branch_history_entry_t;
+    uint8_t idx;
+    uint32_t PC[HISTORY_SIZE];
+    struct rv_insn *target[HISTORY_SIZE];
+} branch_history_table_t;
 
 typedef struct rv_insn {
     union {
@@ -300,8 +301,7 @@ typedef struct rv_insn {
      * specific IR array without the need for additional copying.
      */
     struct rv_insn *branch_taken, *branch_untaken;
-    uint8_t branch_table_count;
-    branch_history_entry_t *branch_table;
+    branch_history_table_t *branch_table;
 } rv_insn_t;
 
 /* decode the RISC-V instruction */

src/emulate.c

@@ -639,8 +639,7 @@ static void block_translate(riscv_t *rv, block_t *block)
                 || ir->opcode == rv_insn_cjalr || ir->opcode == rv_insn_cjr
 #endif
             )
-                ir->branch_table =
-                    calloc(1, HISTORY_SIZE * sizeof(branch_history_entry_t));
+                ir->branch_table = calloc(1, sizeof(branch_history_table_t));
             break;
         }
 

src/rv32_template.c

@@ -49,19 +49,19 @@ RVOP(jal, {
  */
 #define LOOKUP_OR_UPDATE_BRANCH_HISTORY_TABLE()                               \
     /* lookup branch history table */                                         \
-    for (int i = 0; i < ir->branch_table_count; i++) {                        \
-        if (ir->branch_table[i].PC == PC) {                                   \
-            MUST_TAIL return ir->branch_table[i].branch_target->impl(         \
-                rv, ir->branch_table[i].branch_target, cycle, PC);            \
+    for (int i = 0; i < HISTORY_SIZE; i++) {                                  \
+        if (ir->branch_table->PC[i] == PC) {                                  \
+            MUST_TAIL return ir->branch_table->target[i]->impl(               \
+                rv, ir->branch_table->target[i], cycle, PC);                  \
         }                                                                     \
     }                                                                         \
     block_t *block = block_find(&rv->block_map, PC);                          \
     if (block) {                                                              \
         /* update branch history table */                                     \
-        ir->branch_table_count = (ir->branch_table_count + 1) % HISTORY_SIZE; \
-        ir->branch_table[ir->branch_table_count].PC = PC;                     \
-        ir->branch_table[ir->branch_table_count].branch_target =              \
+        ir->branch_table->PC[ir->branch_table->idx] = PC;                     \
+        ir->branch_table->target[ir->branch_table->idx] =                     \
             block->ir_head;                                                   \
+        ir->branch_table->idx = (ir->branch_table->idx + 1) % HISTORY_SIZE;   \
         MUST_TAIL return block->ir_head->impl(rv, block->ir_head, cycle, PC); \
     }