Add a couple of likely annotations.

src/ds/helpers.h

@@ -27,7 +27,7 @@ namespace snmalloc
       // If defined should be initially false;
       assert(first == nullptr || *first == false);
 
-      if (!initialised.load(std::memory_order_acquire))
+      if (unlikely(!initialised.load(std::memory_order_acquire)))
       {
         FlagLock lock(flag);
         if (!initialised)

src/mem/threadalloc.h

@@ -284,7 +284,7 @@ namespace snmalloc
     {
       Alloc*& per_thread = inner_get();
 
-      if (per_thread != nullptr)
+      if (likely(per_thread != nullptr))
         return per_thread;
 
       // Slow path that performs initialization