From ada23c87e7edb50cb238c19ec6334f2da01422cc Mon Sep 17 00:00:00 2001
From: Kornel Benko <kornel@lyx.org>
Date: Mon, 22 Apr 2019 18:49:03 +0200
Subject: [PATCH] Cmake build: Use interprocedural optimization if possible

With gnu compilers this adds -flto and -fno-fat-lto-objects
to compiler and linker flags.
---
 3rdparty/hunspell/CMakeLists.txt |  6 +++++-
 3rdparty/libiconv/CMakeLists.txt |  7 ++++++-
 3rdparty/mythes/CMakeLists.txt   |  6 +++++-
 3rdparty/zlib/CMakeLists.txt     |  7 ++++++-
 CMakeLists.txt                   | 12 ++++++++++++
 5 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/3rdparty/hunspell/CMakeLists.txt b/3rdparty/hunspell/CMakeLists.txt
index 72e5c52133..9dbb56cd79 100644
--- a/3rdparty/hunspell/CMakeLists.txt
+++ b/3rdparty/hunspell/CMakeLists.txt
@@ -1,5 +1,9 @@
 
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.1)
+
+if (POLICY CMP0069)
+  cmake_policy(SET CMP0069 NEW)
+endif()
 
 project(hunspell)
 
diff --git a/3rdparty/libiconv/CMakeLists.txt b/3rdparty/libiconv/CMakeLists.txt
index 68b7dd76c8..7f5c73bf7f 100644
--- a/3rdparty/libiconv/CMakeLists.txt
+++ b/3rdparty/libiconv/CMakeLists.txt
@@ -5,7 +5,12 @@
 # Please note that the package source code is licensed under its own license.
 
 project ( libiconv C )
-cmake_minimum_required ( VERSION 2.8 )
+cmake_minimum_required(VERSION 3.1)
+
+if (POLICY CMP0069)
+  cmake_policy(SET CMP0069 NEW)
+endif()
+
 set(CMAKE_MODULE_PATH .)
 include ( configure.cmake )
 
diff --git a/3rdparty/mythes/CMakeLists.txt b/3rdparty/mythes/CMakeLists.txt
index c6d11780d9..9457df2b73 100644
--- a/3rdparty/mythes/CMakeLists.txt
+++ b/3rdparty/mythes/CMakeLists.txt
@@ -1,4 +1,8 @@
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.1)
+
+if (POLICY CMP0069)
+  cmake_policy(SET CMP0069 NEW)
+endif()
 
 set(VERSION "1.2.5")
 set(SRCDIR ${CMAKE_CURRENT_SOURCE_DIR}/${VERSION})
diff --git a/3rdparty/zlib/CMakeLists.txt b/3rdparty/zlib/CMakeLists.txt
index a9fad6fa54..a8ca489369 100644
--- a/3rdparty/zlib/CMakeLists.txt
+++ b/3rdparty/zlib/CMakeLists.txt
@@ -1,4 +1,9 @@
-cmake_minimum_required(VERSION 2.4.4)
+cmake_minimum_required(VERSION 3.1)
+
+if (POLICY CMP0069)
+  cmake_policy(SET CMP0069 NEW)
+endif()
+
 set(CMAKE_ALLOW_LOOSE_LOOP_CONSTRUCTS ON)
 
 project(zlib C)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index e421c535b9..e8c3c32c94 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -81,6 +81,18 @@ if(NOT help AND NOT HELP)
       message(FATAL_ERROR "Exiting")
     endif()
   endif()
+  # Enable LTO if supported
+  if (POLICY CMP0069)
+    cmake_policy(SET CMP0069 NEW)
+    include(CheckIPOSupported)
+    check_ipo_supported(RESULT result OUTPUT reason LANGUAGES CXX)
+    if(result)
+      message(STATUS "Setting IPO True")
+      set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+    else()
+      message(STATUS "Not setting IPO , result = ${result}, reason = ${reason}")
+    endif()
+  endif()
 endif()
 
 if(UNIX)
-- 
2.39.5