Re: [PATCH 2/2] libstdc++: use new built-in trait __add_const

[Marc Glisse via Gcc-patches]

On Tue, 21 Mar 2023, Ken Matsui via Libstdc++ wrote:

  /// add_const
+#if __has_builtin(__add_const)
+  template<typename _Tp>
+    struct add_const
+    { using type = __add_const(_Tp); };
+#else
  template<typename _Tp>
    struct add_const
    { using type = _Tp const; };
+#endif

Is that really better? You asked elsewhere if you should measure for each 
patch, and I think that at least for such a trivial case, you need to 
demonstrate that there is a point. The drawbacks are obvious: more code in 
libstdc++, non-standard, and more builtins in the compiler.

Using builtins makes more sense for complicated traits where you can save 
several instantiations. Now that you have done a couple simple cases to 
see how it works, I think you should concentrate on the more complicated 
cases.

--
Marc Glisse