Use trivial_abi in THolder

Apply trivial_abi to THolder so it can be passed directly in registers instead of through an invisible reference to caller-allocated memory.
commit_hash:b63c37dd510deb46bb146c54dbab6daa91db588a

3 files changed, 15 insertions, 2 deletions

diff --git a/util/generic/fwd.h b/util/generic/fwd.h
index d07deeb37d6..cfc98dd9902 100644
--- a/util/generic/fwd.h
+++ b/util/generic/fwd.h
@@ -101,7 +101,7 @@ template <class T, class D = TDelete>
 class TAutoPtr;
 
 template <class T, class D = TDelete>
-class THolder;
+class Y_TRIVIAL_ABI THolder;
 
 template <class T, class C, class D = TDelete>
 class TRefCounted;
diff --git a/util/generic/ptr.h b/util/generic/ptr.h
index 04cfe50a425..7219a1c85ca 100644
--- a/util/generic/ptr.h
+++ b/util/generic/ptr.h
@@ -260,7 +260,7 @@ private:
 };
 
 template <class T, class D>
-class THolder: public TPointerBase<THolder<T, D>, T> {
+class Y_TRIVIAL_ABI THolder: public TPointerBase<THolder<T, D>, T> {
 public:
     constexpr THolder() noexcept
         : T_(nullptr)
diff --git a/util/system/compiler.h b/util/system/compiler.h
index db4416a6c65..e716438b97c 100644
--- a/util/system/compiler.h
+++ b/util/system/compiler.h
@@ -839,6 +839,19 @@ Y_FORCE_INLINE void DoNotOptimizeAway(const T&) = delete;
 #endif
 
 /**
+ * @def Y_TRIVIAL_ABI
+ *
+ * Indicates that a class or structure can be considered trivial for the purpose of calls.
+ *
+ * @see https://clang.llvm.org/docs/AttributeReference.html#trivial-abi
+ */
+#if Y_HAS_CPP_ATTRIBUTE(clang::trivial_abi)
+    #define Y_TRIVIAL_ABI [[clang::trivial_abi]]
+#else
+    #define Y_TRIVIAL_ABI
+#endif
+
+/**
  * @def Y_CORO_AWAIT_ELIDABLE
  *
  * A class attribute which can be applied to a coroutine return type.