sdl_impl: Reduce allocations in GetButtonMappingForDevice()

These maps can be constexpr arrays of std::pair.

src/input_common/sdl/sdl_impl.cpp

@@ -3,6 +3,7 @@
 // Refer to the license.txt file included.
 
 #include <algorithm>
+#include <array>
 #include <atomic>
 #include <cmath>
 #include <functional>
@@ -670,11 +671,21 @@ Common::ParamPackage BuildParamPackageForAnalog(int port, const std::string& gui
 } // Anonymous namespace
 
 ButtonMapping SDLState::GetButtonMappingForDevice(const Common::ParamPackage& params) {
+    if (!params.Has("guid") || !params.Has("port")) {
+        return {};
+    }
+    const auto joystick = GetSDLJoystickByGUID(params.Get("guid", ""), params.Get("port", 0));
+    auto* controller = joystick->GetSDLGameController();
+    if (controller == nullptr) {
+        return {};
+    }
+
     // This list is missing ZL/ZR since those are not considered buttons in SDL GameController.
     // We will add those afterwards
     // This list also excludes Screenshot since theres not really a mapping for that
-    std::unordered_map<Settings::NativeButton::Values, SDL_GameControllerButton>
-        switch_to_sdl_button = {
+    using ButtonBindings =
+        std::array<std::pair<Settings::NativeButton::Values, SDL_GameControllerButton>, 17>;
+    static constexpr ButtonBindings switch_to_sdl_button{{
         {Settings::NativeButton::A, SDL_CONTROLLER_BUTTON_B},
         {Settings::NativeButton::B, SDL_CONTROLLER_BUTTON_A},
         {Settings::NativeButton::X, SDL_CONTROLLER_BUTTON_Y},
@@ -692,30 +703,25 @@ ButtonMapping SDLState::GetButtonMappingForDevice(const Common::ParamPackage& pa
         {Settings::NativeButton::SL, SDL_CONTROLLER_BUTTON_LEFTSHOULDER},
         {Settings::NativeButton::SR, SDL_CONTROLLER_BUTTON_RIGHTSHOULDER},
         {Settings::NativeButton::Home, SDL_CONTROLLER_BUTTON_GUIDE},
-        };
-    if (!params.Has("guid") || !params.Has("port")) {
-        return {};
-    }
-    const auto joystick = GetSDLJoystickByGUID(params.Get("guid", ""), params.Get("port", 0));
-    auto* controller = joystick->GetSDLGameController();
-    if (controller == nullptr) {
-        return {};
-    }
+    }};
+
+    // Add the missing bindings for ZL/ZR
+    using ZBindings =
+        std::array<std::pair<Settings::NativeButton::Values, SDL_GameControllerAxis>, 2>;
+    static constexpr ZBindings switch_to_sdl_axis{{
+        {Settings::NativeButton::ZL, SDL_CONTROLLER_AXIS_TRIGGERLEFT},
+        {Settings::NativeButton::ZR, SDL_CONTROLLER_AXIS_TRIGGERRIGHT},
+    }};
+
+    ButtonMapping mapping;
+    mapping.reserve(switch_to_sdl_button.size() + switch_to_sdl_axis.size());
 
-    ButtonMapping mapping{};
     for (const auto& [switch_button, sdl_button] : switch_to_sdl_button) {
         const auto& binding = SDL_GameControllerGetBindForButton(controller, sdl_button);
         mapping.insert_or_assign(
             switch_button,
             BuildParamPackageForBinding(joystick->GetPort(), joystick->GetGUID(), binding));
     }
-
-    // Add the missing bindings for ZL/ZR
-    std::unordered_map<Settings::NativeButton::Values, SDL_GameControllerAxis> switch_to_sdl_axis =
-        {
-            {Settings::NativeButton::ZL, SDL_CONTROLLER_AXIS_TRIGGERLEFT},
-            {Settings::NativeButton::ZR, SDL_CONTROLLER_AXIS_TRIGGERRIGHT},
-        };
     for (const auto& [switch_button, sdl_axis] : switch_to_sdl_axis) {
         const auto& binding = SDL_GameControllerGetBindForAxis(controller, sdl_axis);
         mapping.insert_or_assign(