From 997206a1aeea2abc0e331bcbb10f939f52670aa2 Mon Sep 17 00:00:00 2001
From: Jonathan Poelen <jonathan.poelen@gmail.com>
Date: Tue, 20 Jun 2023 01:42:00 +0200
Subject: [PATCH] optimize mp_map_replace

compiler |       gcc-12       |      clang-15
before   | 0:00.46s - 187160K | 0:00.38s - 129104K
after    | 0:00.21s - 80236K  | 0:00.33s - 123644K

```cpp
using namespace boost::mp11;

template<class L, class M = mp_transform<mp_list, L>>
struct f { template<class I> using g = mp_map_replace<M, mp_list<I, I>>; };

template<class I, class L = mp_iota<I>> using test
  = mp_transform<f<L>::template g, L>;

using r1 = mp_transform<test, mp_iota_c<30>>;
```
---
 include/boost/mp11/map.hpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/boost/mp11/map.hpp b/include/boost/mp11/map.hpp
index b9581ac..5141d2e 100644
--- a/include/boost/mp11/map.hpp
+++ b/include/boost/mp11/map.hpp
@@ -38,11 +38,19 @@ template<template<class...> class M, class... U, class T> struct mp_map_replace_
 {
     using K = mp_first<T>;
 
-    // mp_replace_if is inlined here using a struct _f because of msvc-14.0
+#if BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1920 )
 
     template<class V> struct _f { using type = mp_if< std::is_same<mp_first<V>, K>, T, V >; };
 
     using type = mp_if< mp_map_contains<M<U...>, K>, M<typename _f<U>::type...>, M<U..., T> >;
+
+#else
+
+    template<class V> using _f = mp_if< std::is_same<mp_first<V>, K>, T, V >;
+
+    using type = mp_if< mp_map_contains<M<U...>, K>, M<_f<U>...>, M<U..., T> >;
+
+#endif
 };
 
 } // namespace detail