fix(S3FIFO): keep the 64-bit frequency when the main FIFO evicts

libCacheSim/cache/eviction/Clock2QPlus.c

@@ -367,7 +367,7 @@ static void Clock2QPlus_evict_main(cache_t *cache, const request_t *req) {
   while (!has_evicted && main->get_occupied_byte(main) > 0) {
     cache_obj_t *obj_to_evict = main->to_evict(main, req);
     DEBUG_ASSERT(obj_to_evict != NULL);
-    int freq = obj_to_evict->Clock2QPlus.freq;
+    int64_t freq = obj_to_evict->Clock2QPlus.freq;
     copy_cache_obj_to_request(params->req_local, obj_to_evict);
     if (freq >= 1) {
       // we need to evict first because the object to insert has the same obj_id

libCacheSim/cache/eviction/S3FIFO.c

@@ -377,7 +377,7 @@ static void S3FIFO_evict_main(cache_t *cache, const request_t *req) {
   while (!has_evicted && main_fifo->get_occupied_byte(main_fifo) > 0) {
     cache_obj_t *obj_to_evict = main_fifo->to_evict(main_fifo, req);
     DEBUG_ASSERT(obj_to_evict != NULL);
-    int freq = obj_to_evict->S3FIFO.freq;
+    int64_t freq = obj_to_evict->S3FIFO.freq;
     copy_cache_obj_to_request(params->req_local, obj_to_evict);
     if (freq >= 1) {
       // we need to evict first because the object to insert has the same obj_id

libCacheSim/cache/eviction/S3FIFOv0.c

@@ -374,7 +374,7 @@ static void S3FIFOv0_evict_main(cache_t *cache, const request_t *req) {
   while (!has_evicted && main_fifo->get_occupied_byte(main_fifo) > 0) {
     cache_obj_t *obj_to_evict = main_fifo->to_evict(main_fifo, req);
     DEBUG_ASSERT(obj_to_evict != NULL);
-    int freq = obj_to_evict->S3FIFO.freq;
+    int64_t freq = obj_to_evict->S3FIFO.freq;
 #if defined(TRACK_EVICTION_V_AGE)
     int64_t create_time = obj_to_evict->create_time;
 #endif

test/test_evictionAlgo.c

@@ -392,6 +392,47 @@ static void test_S3FIFO(gconstpointer user_data) {
   test_cache_algorithm(user_data, &test_data_truth[21]);
 }
 
+// An object read more than INT32_MAX times since the main FIFO last passed it
+// is the hottest object in the cache. Its 64-bit counter must survive the
+// eviction loop's local copy, or the loop sees a negative count and evicts it.
+static void test_S3FIFO_main_freq_beyond_int32(void) {
+  common_cache_params_t cc_params = {.cache_size = 100, .hashpower = 8};
+  cache_t *cache = S3FIFO_init(cc_params, NULL);
+  request_t *req = new_request();
+  req->obj_size = 1;
+
+  // Objects 1 to 10 fill the small FIFO and 11 to 100 go straight to main,
+  // since nothing has been evicted yet. Two reads each promote 1 to 10.
+  for (obj_id_t id = 1; id <= 100; id++) {
+    req->obj_id = id;
+    cache->get(cache, req);
+  }
+  for (int round = 0; round < 2; round++) {
+    for (obj_id_t id = 1; id <= 10; id++) {
+      req->obj_id = id;
+      cache->get(cache, req);
+    }
+  }
+
+  // Object 11 is the oldest in main. Give it 2^31 reads.
+  req->obj_id = 11;
+  cache_obj_t *hot = cache->find(cache, req, false);
+  g_assert_nonnull(hot);
+  hot->S3FIFO.freq = (int64_t)INT32_MAX + 1;
+
+  // The next miss promotes 1 to 10, overfilling main, so main evicts from its
+  // head. Object 11 must be reinserted, and object 12 evicted in its place.
+  req->obj_id = 101;
+  cache->get(cache, req);
+  req->obj_id = 11;
+  g_assert_nonnull(cache->find(cache, req, false));
+  req->obj_id = 12;
+  g_assert_null(cache->find(cache, req, false));
+
+  free_request(req);
+  cache->cache_free(cache);
+}
+
 static void test_S3FIFOv0(gconstpointer user_data) {
   test_cache_algorithm(user_data, &test_data_truth[22]);
 }
@@ -474,6 +515,8 @@ int main(int argc, char *argv[]) {
                        test_QDLP_FIFO);
   g_test_add_data_func("/libCacheSim/cacheAlgo_Random", reader, test_Random);
   g_test_add_data_func("/libCacheSim/cacheAlgo_S3FIFO", reader, test_S3FIFO);
+  g_test_add_func("/libCacheSim/cacheAlgo_S3FIFO_main_freq_beyond_int32",
+                  test_S3FIFO_main_freq_beyond_int32);
   g_test_add_data_func("/libCacheSim/cacheAlgo_S3FIFOv0", reader,
                        test_S3FIFOv0);
 #if defined(ENABLE_S4FIFO) && ENABLE_S4FIFO == 1