From fa46ba16bfab6884864eb63936e5b61fa0a8b6bd Mon Sep 17 00:00:00 2001
From: Connor McLaughlin <stenzek@gmail.com>
Date: Fri, 25 Sep 2020 22:00:53 +1000
Subject: [PATCH] CMake: Re-enable LTO for Release builds with CMake >= 3.9

If you're using an earlier version, I suggest you upgrade, CMake 3.9 was
released in 2017....
---
 CMakeLists.txt | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 07c85f387..861662dd0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -145,7 +145,19 @@ if(MSVC)
 
   # Enable LTO/LTCG on Release builds.
   if(${CMAKE_BUILD_TYPE} STREQUAL "Release")
-    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION ON)
+    if (${CMAKE_VERSION} VERSION_LESS "3.9.0")
+      message(WARNING "CMake version is less than 3.9.0, we can't enable LTCG/IPO. This will make the build slightly slower, consider updating your CMake version.")
+    else()
+      cmake_policy(SET CMP0069 NEW)
+      include(CheckIPOSupported)
+      check_ipo_supported(RESULT IPO_IS_SUPPORTED)
+      if(IPO_IS_SUPPORTED)
+        message(STATUS "Enabling LTCG/IPO.")
+        set(CMAKE_INTERPROCEDURAL_OPTIMIZATION ON)
+      else()
+        message(WARNING "LTCG/IPO is not supported, this will make the build slightly slower.")
+      endif()
+    endif()
   endif()
 endif()