From 58f0d81925ec055143065f5305cc044240f0ae8b Mon Sep 17 00:00:00 2001
From: Daniel Lemire <lemire@gmail.com>
Date: Thu, 9 May 2019 21:17:13 -0400
Subject: [PATCH] Fixing issue 99

---
 CMakeLists.txt            | 10 +++++++---
 tools/cmake/FindLTO.cmake | 25 -------------------------
 2 files changed, 7 insertions(+), 28 deletions(-)
 delete mode 100644 tools/cmake/FindLTO.cmake

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e572564de..eba125851 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,10 @@
-cmake_minimum_required(VERSION 3.8...3.13)
+cmake_minimum_required(VERSION 3.9) # CMP0069 NEW
+include(CheckIPOSupported)
+check_ipo_supported(RESULT ltoresult)
+if(ltoresult)
+set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+endif()
+
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_MACOSX_RPATH OFF)
@@ -20,14 +26,12 @@ option(SIMDJSON_BUILD_STATIC "Build a static library" OFF) # turning it on disab
 else()
 option(SIMDJSON_BUILD_STATIC "Build a static library" ON) # turning it on disables the production of a dynamic library
 endif()
-option(SIMDJSON_BUILD_LTO "Build library with Link Time Optimization" OFF)
 option(SIMDJSON_SANITIZE "Sanitize addresses" OFF)
 
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/tools/cmake")
 
 find_package(CTargets)
 find_package(Options)
-find_package(LTO)
 
 install(DIRECTORY include/${SIMDJSON_LIB_NAME} DESTINATION include)
 set (TEST_DATA_DIR "${CMAKE_CURRENT_SOURCE_DIR}/jsonchecker/")
diff --git a/tools/cmake/FindLTO.cmake b/tools/cmake/FindLTO.cmake
deleted file mode 100644
index 147470f6a..000000000
--- a/tools/cmake/FindLTO.cmake
+++ /dev/null
@@ -1,25 +0,0 @@
-# gcc and clang require a special 'ar' and 'ranlib' to create a
-# static libX.a that allows for further inlining, but icc does not.
-
-macro(append var string)
-  set(${var} "${${var}} ${string}")
-endmacro(append)
-
-if(BUILD_LTO) 
-  if ("${CMAKE_C_COMPILER_ID}" MATCHES "Intel") # icc 
-    append(CMAKE_CXX_FLAGS "-ipo")
-  elseif("${CMAKE_C_COMPILER_ID}" MATCHES "MSVC") # Microsoft
-    # TODO
-  elseif ("${CMAKE_C_COMPILER_ID}" MATCHES "Clang") # Clang or AppleClang
-    append(CMAKE_CXX_FLAGS "-flto")
-    append(CMAKE_EXE_LINKER_FLAGS "-fuse-ld=gold -flto")
-    append(CMAKE_SHARED_LINKER_FLAGS "-fuse-ld=gold -flto")
-    set(_LLVM_VERSION_STRING "3.8") # FIXME: determine version automatically
-    set(CMAKE_AR "llvm-ar-${_LLVM_VERSION_STRING}")
-    set(CMAKE_RANLIB "llvm-ranlib-${_LLVM_VERSION_STRING}")
-  else() # assume GCC compatible syntax if not matched
-    append(CMAKE_CXX_FLAGS "-flto")
-    set(CMAKE_AR "gcc-ar")
-    set(CMAKE_RANLIB "gcc-ranlib")
-  endif()
-endif(BUILD_LTO)