libstdc++: Skip tag dispatching for _S_relocate in C++17

In C++17 mode all callers of _S_relocate have already done:

  if constexpr (_S_use_relocate())

so we don't need to repeat that check and use tag dispatching to avoid
ill-formed instantiations.

libstdc++-v3/ChangeLog:

	* include/bits/stl_vector.h (vector::_S_do_relocate): Remove
	C++20 constexpr specifier.
	(vector::_S_relocate) [__cpp_if_constexpr]: Call __relocate_a
	directly without tag dispatching.

diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index 4587757637ebe9e70e68726590017ae6a3392810..36b2cff3d78c5e88c7881bded77159fbc63911f6 100644 (file)
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -481,14 +481,14 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        return _S_nothrow_relocate(__is_move_insertable<_Tp_alloc_type>{});
       }
 
-      static _GLIBCXX20_CONSTEXPR pointer
+      static pointer
       _S_do_relocate(pointer __first, pointer __last, pointer __result,
                     _Tp_alloc_type& __alloc, true_type) noexcept
       {
        return std::__relocate_a(__first, __last, __result, __alloc);
       }
 
-      static _GLIBCXX20_CONSTEXPR pointer
+      static pointer
       _S_do_relocate(pointer, pointer, pointer __result,
                     _Tp_alloc_type&, false_type) noexcept
       { return __result; }
@@ -497,8 +497,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _S_relocate(pointer __first, pointer __last, pointer __result,
                  _Tp_alloc_type& __alloc) noexcept
       {
+#if __cpp_if_constexpr
+       // All callers have already checked _S_use_relocate() so just do it.
+       return std::__relocate_a(__first, __last, __result, __alloc);
+#else
        using __do_it = __bool_constant<_S_use_relocate()>;
        return _S_do_relocate(__first, __last, __result, __alloc, __do_it{});
+#endif
       }
 #endif // C++11