no need for XCHGL, MOVL is enough?

Author: maurycy

Python/gc.c

@@ -1400,9 +1400,10 @@ static void
 add_stats(GCState *gcstate, int gen, struct gc_generation_stats *stats)
 {
     struct gc_stats *generation_stats = gcstate->generation_stats;
-    uint32_t seq = _Py_atomic_load_uint32(&generation_stats->update_seq);
+    uint32_t seq = _Py_atomic_load_uint32_relaxed(&generation_stats->update_seq);
     assert((seq & 1) == 0);
-    _Py_atomic_store_uint32(&generation_stats->update_seq, seq + 1);
+    /* Odd seq tells the reader that an update is in progress. */
+    _Py_atomic_store_uint32_relaxed(&generation_stats->update_seq, seq + 1);
     _Py_atomic_fence_seq_cst();
 
     struct gc_generation_stats *prev_stats = gc_get_prev_stats(gcstate, gen);
@@ -1419,7 +1420,7 @@ add_stats(GCState *gcstate, int gen, struct gc_generation_stats *stats)
     cur_stats->duration += stats->duration;
     cur_stats->heap_size = stats->heap_size;
     cur_stats->ts_stop = stats->ts_stop;
-    _Py_atomic_store_uint32(&generation_stats->update_seq, seq + 2);
+    _Py_atomic_store_uint32_release(&generation_stats->update_seq, seq + 2);
 }
 
 /* This is the main function.  Read this to understand how the

Python/gc_free_threading.c

@@ -2284,9 +2284,10 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     /* Update stats. */
     PyMutex_Lock(&gcstate->stats_mutex);
     struct gc_stats *generation_stats = gcstate->generation_stats;
-    uint32_t seq = _Py_atomic_load_uint32(&generation_stats->update_seq);
+    uint32_t seq = _Py_atomic_load_uint32_relaxed(&generation_stats->update_seq);
     assert((seq & 1) == 0);
-    _Py_atomic_store_uint32(&generation_stats->update_seq, seq + 1);
+    /* Odd seq tells the reader that an update is in progress. */
+    _Py_atomic_store_uint32_relaxed(&generation_stats->update_seq, seq + 1);
     _Py_atomic_fence_seq_cst();
     struct gc_generation_stats *stats = get_stats(gcstate, generation);
     stats->ts_start = start;
@@ -2296,7 +2297,7 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     stats->uncollectable += n;
     stats->duration += duration;
     stats->candidates += state.candidates;
-    _Py_atomic_store_uint32(&generation_stats->update_seq, seq + 2);
+    _Py_atomic_store_uint32_release(&generation_stats->update_seq, seq + 2);
     PyMutex_Unlock(&gcstate->stats_mutex);
 
     GC_STAT_ADD(generation, objects_collected, m);