From 4caf0e4cb9153355239294ed96483bf49eb705a2 Mon Sep 17 00:00:00 2001
From: sfan5 <sfan5@live.de>
Date: Sun, 25 Feb 2024 20:58:42 +0100
Subject: [PATCH] Update LTO exclusion list (#14407)

---
 CMakeLists.txt          | 40 ++++++++++++++++++++++++++--------------
 doc/compiling/README.md |  2 +-
 2 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 47f1367a0..fefcef2c9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,6 +42,18 @@ set(DEFAULT_ENABLE_LTO TRUE)
 if(CMAKE_BUILD_TYPE STREQUAL "Debug")
   set(DEFAULT_ENABLE_LTO FALSE)
 endif()
+#### LTO testing list ####
+# - Linux: seems to work always
+# - win32/msvc: works
+# - win32/gcc: fails to link
+# - win32/clang: works
+# - macOS on x86: seems to be fine
+# - macOS on ARM: crashes, see <https://github.com/minetest/minetest/issues/14397>
+# Note: since CMake has no easy architecture detection disabling for Mac entirely
+#### ####
+if((WIN32 AND CMAKE_CXX_COMPILER_ID STREQUAL "GNU") OR APPLE)
+	set(DEFAULT_ENABLE_LTO FALSE)
+endif()
 set(ENABLE_LTO ${DEFAULT_ENABLE_LTO} CACHE BOOL "Use Link Time Optimization")
 
 set(DEFAULT_RUN_IN_PLACE FALSE)
@@ -66,20 +78,6 @@ if(NOT CMAKE_BUILD_TYPE)
 	set(CMAKE_BUILD_TYPE Release CACHE STRING "Build type: Debug or Release" FORCE)
 endif()
 
-# FIXME: Windows build fails in multiple places to link, needs to be investigated.
-if (ENABLE_LTO AND NOT WIN32)
-	include(CheckIPOSupported)
-	check_ipo_supported(RESULT lto_supported OUTPUT lto_output)
-	if(lto_supported)
-		set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
-		message(STATUS "LTO/IPO is enabled")
-	else()
-		message(STATUS "LTO/IPO requested but it is not supported by the compiler: ${lto_output}")
-	endif()
-else()
-	message(STATUS "LTO/IPO is not enabled")
-endif()
-
 set(ENABLE_UPDATE_CHECKER (NOT ${DEVELOPMENT_BUILD}) CACHE BOOL
 	"Whether to enable update checks by default")
 
@@ -163,6 +161,20 @@ elseif(BUILD_CLIENT AND TARGET IrrlichtMt::IrrlichtMt)
 	endif()
 endif()
 
+if (ENABLE_LTO OR CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+	include(CheckIPOSupported)
+	check_ipo_supported(RESULT lto_supported OUTPUT lto_output)
+	if(lto_supported)
+		set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+		message(STATUS "LTO/IPO is enabled")
+	else()
+		set(CMAKE_INTERPROCEDURAL_OPTIMIZATION FALSE)
+		message(STATUS "LTO/IPO was requested but is not supported by the compiler: ${lto_output}")
+	endif()
+else()
+	message(STATUS "LTO/IPO is not enabled")
+endif()
+
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
 	if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "${GCC_MINIMUM_VERSION}")
 		message(FATAL_ERROR "Insufficient gcc version, found ${CMAKE_CXX_COMPILER_VERSION}. "
diff --git a/doc/compiling/README.md b/doc/compiling/README.md
index 7ce06c2de..4ecaa88bb 100644
--- a/doc/compiling/README.md
+++ b/doc/compiling/README.md
@@ -28,7 +28,7 @@ General options and their default values:
     ENABLE_REDIS=ON            - Build with libhiredis; Enables use of Redis map backend
     ENABLE_SPATIAL=ON          - Build with LibSpatial; Speeds up AreaStores
     ENABLE_SOUND=ON            - Build with OpenAL, libogg & libvorbis; in-game sounds
-    ENABLE_LTO=ON              - Build with IPO/LTO optimizations (smaller and more efficient than regular build)
+    ENABLE_LTO=<varies>        - Build with IPO/LTO optimizations (smaller and more efficient than regular build)
     ENABLE_LUAJIT=ON           - Build with LuaJIT (much faster than non-JIT Lua)
     ENABLE_PROMETHEUS=OFF      - Build with Prometheus metrics exporter (listens on tcp/30000 by default)
     ENABLE_SYSTEM_GMP=ON       - Use GMP from system (much faster than bundled mini-gmp)