Fix #9386: compilers failing to compile with LTO by using variants instead of new + unique_ptr

With std::variant all memory can be figured out at compile time, so the compiler needs to keep track of fewer elements. It also saves out a unique_ptr and its memory management, over a slight impact for resolving a setting.

10 files changed, 13 insertions, 11 deletions

diff --git a/src/settings.cpp b/src/settings.cpp
index 5e3ba5be7..9d0e125b0 100644
--- a/src/settings.cpp
+++ b/src/settings.cpp
@@ -87,6 +87,7 @@ std::string _config_file; ///< Configuration file of OpenTTD
 typedef std::list<ErrorMessageData> ErrorList;
 static ErrorList _settings_error_list; ///< Errors while loading minimal settings.
 
+typedef span<const SettingVariant> SettingTable;
 
 typedef void SettingDescProc(IniFile *ini, const SettingTable &desc, const char *grpname, void *object, bool only_startup);
 typedef void SettingDescProcList(IniFile *ini, const char *grpname, StringList &list);
@@ -98,9 +99,9 @@ static bool IsSignedVarMemType(VarType vt);
  * @param desc The type of the iterator of the value in SettingTable.
  * @return The actual pointer to SettingDesc.
  */
-static const SettingDesc *GetSettingDesc(const std::unique_ptr<const SettingDesc> &desc)
+static constexpr const SettingDesc *GetSettingDesc(const SettingVariant &desc)
 {
-	return desc.get();
+	return std::visit([](auto&& arg) -> const SettingDesc * { return &arg; }, desc);
 }
 
 /**
diff --git a/src/settings_internal.h b/src/settings_internal.h
index 5b35d328a..0e6637a5b 100644
--- a/src/settings_internal.h
+++ b/src/settings_internal.h
@@ -10,6 +10,7 @@
 #ifndef SETTINGS_INTERNAL_H
 #define SETTINGS_INTERNAL_H
 
+#include <variant>
 #include "saveload/saveload.h"
 
 enum SettingFlag : uint16 {
@@ -299,7 +300,7 @@ struct NullSettingDesc : SettingDesc {
 	bool IsSameValue(const IniItem *item, void *object) const override { NOT_REACHED(); }
 };
 
-typedef std::initializer_list<std::unique_ptr<const SettingDesc>> SettingTable;
+typedef std::variant<IntSettingDesc, BoolSettingDesc, OneOfManySettingDesc, ManyOfManySettingDesc, StringSettingDesc, ListSettingDesc, NullSettingDesc> SettingVariant;
 
 const SettingDesc *GetSettingFromName(const std::string_view name);
 void GetSettingSaveLoadByPrefix(const std::string_view prefix, std::vector<SaveLoad> &saveloads);
diff --git a/src/table/settings.h.preamble b/src/table/settings.h.preamble
index c9b47626c..5fd1a9bac 100644
--- a/src/table/settings.h.preamble
+++ b/src/table/settings.h.preamble
@@ -54,7 +54,7 @@ static size_t ConvertLandscape(const char *value);
  * on the appropriate macro.
  */
 
-#define NSD(type, ...) std::unique_ptr<const SettingDesc>(new type##SettingDesc(__VA_ARGS__))
+#define NSD(type, ...) SettingVariant { std::in_place_type<type##SettingDesc>, __VA_ARGS__ }
 
 /* Macros for various objects to go in the configuration file.
  * This section is for global variables */
diff --git a/src/table/settings/company_settings.ini b/src/table/settings/company_settings.ini
index 71f99d5a2..e5019305f 100644
--- a/src/table/settings/company_settings.ini
+++ b/src/table/settings/company_settings.ini
@@ -12,7 +12,7 @@ static void UpdateAllServiceInterval(int32 new_value);
 static bool CanUpdateServiceInterval(VehicleType type, int32 &new_value);
 static void UpdateServiceInterval(VehicleType type, int32 new_value);
 
-static const SettingTable _company_settings{
+static const SettingVariant _company_settings[] = {
 [post-amble]
 };
 [templates]
diff --git a/src/table/settings/currency_settings.ini b/src/table/settings/currency_settings.ini
index c8ba3d76c..d0950db8e 100644
--- a/src/table/settings/currency_settings.ini
+++ b/src/table/settings/currency_settings.ini
@@ -7,7 +7,7 @@
 ; Settings for the in-game custom currency.
 
 [pre-amble]
-static const SettingTable _currency_settings{
+static const SettingVariant _currency_settings[] = {
 [post-amble]
 };
 [templates]
diff --git a/src/table/settings/gameopt_settings.ini b/src/table/settings/gameopt_settings.ini
index ce28def63..447400623 100644
--- a/src/table/settings/gameopt_settings.ini
+++ b/src/table/settings/gameopt_settings.ini
@@ -33,7 +33,7 @@ static std::initializer_list<const char*> _osk_activation{"disabled", "double",
 static std::initializer_list<const char*> _settings_profiles{"easy", "medium", "hard"};
 static std::initializer_list<const char*> _news_display{ "off", "summarized", "full"};
 
-static const SettingTable _gameopt_settings{
+static const SettingVariant _gameopt_settings[] = {
 /* In version 4 a new difficulty setting has been added to the difficulty settings,
  * town attitude towards demolishing. Needs special handling because some dimwit thought
  * it funny to have the GameDifficulty struct be an array while it is a struct of
diff --git a/src/table/settings/misc_settings.ini b/src/table/settings/misc_settings.ini
index 453c6e816..9f73573b2 100644
--- a/src/table/settings/misc_settings.ini
+++ b/src/table/settings/misc_settings.ini
@@ -20,7 +20,7 @@ extern bool _allow_hidpi_window;
 #define WITHOUT_COCOA
 #endif
 
-static const SettingTable _misc_settings{
+static const SettingVariant _misc_settings[] = {
 [post-amble]
 };
 [templates]
diff --git a/src/table/settings/settings.ini b/src/table/settings/settings.ini
index 6fe4d9d51..a0a835364 100644
--- a/src/table/settings/settings.ini
+++ b/src/table/settings/settings.ini
@@ -49,7 +49,7 @@ static void UpdateClientConfigValues();
  * assigns its own value. If the setting was company-based, that would mean that
  * vehicles could decide on different moments that they are heading back to a
  * service depot, causing desyncs on a massive scale. */
-const SettingTable _settings{
+static const SettingVariant _settings[] = {
 [post-amble]
 };
 [templates]
diff --git a/src/table/settings/win32_settings.ini b/src/table/settings/win32_settings.ini
index df1e0cb27..51b579629 100644
--- a/src/table/settings/win32_settings.ini
+++ b/src/table/settings/win32_settings.ini
@@ -12,7 +12,7 @@
 #if defined(_WIN32) && !defined(DEDICATED)
 extern bool _window_maximize;
 
-static const SettingTable _win32_settings{
+static const SettingVariant _win32_settings[] = {
 [post-amble]
 };
 #endif /* _WIN32 */
diff --git a/src/table/settings/window_settings.ini b/src/table/settings/window_settings.ini
index 3a7669754..d9327aa92 100644
--- a/src/table/settings/window_settings.ini
+++ b/src/table/settings/window_settings.ini
@@ -9,7 +9,7 @@
 
 [pre-amble]
 
-static const SettingTable _window_settings{
+static const SettingVariant _window_settings[] = {
 [post-amble]
 };
 [templates]