[oneDPL][tbb] + memory leaks fix (sort/stable sort, tbb backend) (#1589)

include/oneapi/dpl/pstl/parallel_backend_tbb.h

@@ -510,7 +510,7 @@ class __root_task
     friend class __func_task<_Func>;
 };
 
-#else  // TBB_INTERFACE_VERSION <= 12000
+#else  // TBB_INTERFACE_VERSION > 12000
 class __task : public tbb::detail::d1::task
 {
   protected:
@@ -644,10 +644,16 @@ class __func_task : public __task
 
         assert(__parent != nullptr);
         assert(__parent->_M_refcount.load(::std::memory_order_relaxed) > 0);
-        if (--__parent->_M_refcount == 0)
+
+        auto __refcount = --__parent->_M_refcount;
+
+        // Placing the deallocation after the refcount decrement allows another thread to proceed with tree
+        // folding concurrently with this task cleanup.
+        __alloc.deallocate(this, *__ed);
+
+        if (__refcount == 0)
         {
             assert(__next == nullptr);
-            __alloc.deallocate(this, *__ed);
             return __parent;
         }