[libcxx-commits] [libcxx] [libc++] Specialize allocator_traits for std::allocator (PR #160278)

[Nikolas Klauser via libcxx-commits]

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@@ -338,6 +339,80 @@ struct allocator_traits {
   }
 };
 
+template <class _Tp>
+struct allocator_traits<allocator<_Tp> > {
+  using allocator_type                         = allocator<_Tp>;
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philnik777 wrote:

We do get some of the benefit when only specializing the aliases, but we don't get the full benefit. I've tried switching to `if constexpr` for the implementation of the functions, and that got us most of the way to a full specialization (only ~twice as slow). I think this approach is fine, and we can get the benefit of `if constexpr` here once we drop C++03.

https://github.com/llvm/llvm-project/pull/160278