Add caching to Config::Info

The goal of this change is to make Config::Get(const Info<T>&)
fast so that we can use it in hot paths.

Source/Core/Common/Config/ConfigInfo.h

@@ -4,9 +4,13 @@
 
 #pragma once
 
+#include <mutex>
+#include <shared_mutex>
 #include <string>
 #include <type_traits>
+#include <utility>
 
+#include "Common/CommonTypes.h"
 #include "Common/Config/Enums.h"
 
 namespace Config
@@ -29,30 +33,93 @@ struct Location
   bool operator<(const Location& other) const;
 };
 
+template <typename T>
+struct CachedValue
+{
+  T value;
+  u64 config_version;
+};
+
 template <typename T>
 class Info
 {
 public:
   constexpr Info(const Location& location, const T& default_value)
-      : m_location{location}, m_default_value{default_value}
+      : m_location{location}, m_default_value{default_value}, m_cached_value{default_value, 0}
   {
   }
 
+  Info(const Info<T>& other) { *this = other; }
+
+  // Not thread-safe
+  Info(Info<T>&& other) { *this = std::move(other); }
+
+  // Make it easy to convert Info<Enum> into Info<UnderlyingType<Enum>>
+  // so that enum settings can still easily work with code that doesn't care about the enum values.
+  template <typename Enum,
+            std::enable_if_t<std::is_same<T, detail::UnderlyingType<Enum>>::value>* = nullptr>
+  Info(const Info<Enum>& other)
+  {
+    *this = other;
+  }
+
+  Info<T>& operator=(const Info<T>& other)
+  {
+    m_location = other.GetLocation();
+    m_default_value = other.GetDefaultValue();
+    m_cached_value = other.GetCachedValue();
+    return *this;
+  }
+
+  // Not thread-safe
+  Info<T>& operator=(Info<T>&& other)
+  {
+    m_location = std::move(other.m_location);
+    m_default_value = std::move(other.m_default_value);
+    m_cached_value = std::move(other.m_cached_value);
+    return *this;
+  }
+
   // Make it easy to convert Info<Enum> into Info<UnderlyingType<Enum>>
   // so that enum settings can still easily work with code that doesn't care about the enum values.
   template <typename Enum,
             std::enable_if_t<std::is_same<T, detail::UnderlyingType<Enum>>::value>* = nullptr>
-  constexpr Info(const Info<Enum>& other)
-      : m_location{other.GetLocation()}, m_default_value{static_cast<detail::UnderlyingType<Enum>>(
-                                             other.GetDefaultValue())}
+  Info<T>& operator=(const Info<Enum>& other)
   {
+    m_location = other.GetLocation();
+    m_default_value = static_cast<T>(other.GetDefaultValue());
+    m_cached_value = other.template GetCachedValueCasted<T>();
+    return *this;
   }
 
   constexpr const Location& GetLocation() const { return m_location; }
   constexpr const T& GetDefaultValue() const { return m_default_value; }
 
+  CachedValue<T> GetCachedValue() const
+  {
+    std::shared_lock lock(m_cached_value_mutex);
+    return m_cached_value;
+  }
+
+  template <typename U>
+  CachedValue<U> GetCachedValueCasted() const
+  {
+    std::shared_lock lock(m_cached_value_mutex);
+    return CachedValue<U>{static_cast<U>(m_cached_value.value), m_cached_value.config_version};
+  }
+
+  void SetCachedValue(const CachedValue<T>& cached_value) const
+  {
+    std::unique_lock lock(m_cached_value_mutex);
+    if (m_cached_value.config_version < cached_value.config_version)
+      m_cached_value = cached_value;
+  }
+
 private:
   Location m_location;
   T m_default_value;
+
+  mutable CachedValue<T> m_cached_value;
+  mutable std::shared_mutex m_cached_value_mutex;
 };
 }  // namespace Config