From 9c8960cf5ffe63ab5a48595d65bed44bad5ba474 Mon Sep 17 00:00:00 2001
From: Luke Street <luke.street@encounterpc.com>
Date: Sat, 30 Nov 2019 23:01:38 -0500
Subject: [PATCH] Use lld with clang, gold with gcc, LTO only on release builds

---
 CMakeLists.txt | 64 +++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 50 insertions(+), 14 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5dbaf06dd..204ed1b69 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -156,24 +156,60 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
   link_directories(/usr/local/lib)
 endif()
 
-if(("${CMAKE_BUILD_TYPE}" STREQUAL "Release" OR "${CMAKE_BUILD_TYPE}" STREQUAL "RelWithDebInfo")
-   AND "${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
-  option(USE_LD_GOLD "Link with GNU Gold and enable LTO" ON)
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
+  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+    option(USE_LD_LLD "Link with LLD" ON)
+  elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
+    option(USE_LD_GOLD "Link with GNU Gold" ON)
+  endif()
+
+  include(CheckIPOSupported)
+  check_ipo_supported(RESULT LTO_SUPPORTED)
+  if(LTO_SUPPORTED AND ("${CMAKE_BUILD_TYPE}" STREQUAL "Release" OR "${CMAKE_BUILD_TYPE}" STREQUAL "RelWithDebInfo"))
+    option(USE_LTO "Enable LTO" ON)
+  else()
+    option(USE_LTO "Enable LTO" OFF)
+  endif()
 else()
-  option(USE_LD_GOLD "Link with GNU Gold and enable LTO" OFF)
+  option(USE_LD_LLD "Link with LLD" OFF)
+  option(USE_LD_GOLD "Link with GNU Gold" OFF)
+  option(USE_LTO "Enable LTO" OFF)
 endif()
-if(USE_LD_GOLD AND ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU"))
-    execute_process(COMMAND ${CMAKE_C_COMPILER} -fuse-ld=gold -Wl,--version ERROR_QUIET OUTPUT_VARIABLE LD_VERSION)
-    if("${LD_VERSION}" MATCHES "GNU gold")
-       set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=gold -Wl,--disable-new-dtags")
-       set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -fuse-ld=gold -Wl,--disable-new-dtags")
-       add_compile_options(-flto=thin)
-       add_link_options(-flto=thin)
-       message(STATUS "GNU gold linker enabled.")
+if(USE_LD_LLD)
+  execute_process(COMMAND ${CMAKE_C_COMPILER} -fuse-ld=lld -Wl,--version ERROR_QUIET OUTPUT_VARIABLE LD_VERSION)
+  if("${LD_VERSION}" MATCHES "LLD")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=lld")
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -fuse-ld=lld")
+    if(USE_LTO)
+      add_compile_options(-flto=thin)
+      add_link_options(-flto=thin)
+      message(STATUS "LLD linker enabled with LTO.")
     else()
-       message(WARNING "GNU gold linker isn't available, using the default system linker.")
-       set(USE_LD_GOLD OFF)
+      message(STATUS "LLD linker enabled.")
     endif()
+    set(USE_LD_GOLD OFF)
+  else()
+    message(WARNING "LLD linker isn't available, using the default system linker.")
+    set(USE_LD_LLD OFF)
+  endif()
+endif()
+if(USE_LD_GOLD)
+  execute_process(COMMAND ${CMAKE_C_COMPILER} -fuse-ld=gold -Wl,--version ERROR_QUIET OUTPUT_VARIABLE LD_VERSION)
+  if("${LD_VERSION}" MATCHES "GNU gold")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=gold -Wl,--disable-new-dtags")
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -fuse-ld=gold -Wl,--disable-new-dtags")
+    if(USE_LTO)
+      add_compile_options(-flto=thin)
+      add_link_options(-flto=thin)
+      message(STATUS "GNU gold linker enabled with LTO.")
+    else()
+      message(STATUS "GNU gold linker enabled.")
+    endif()
+    set(USE_LD_LLD OFF)
+  else()
+    message(WARNING "GNU gold linker isn't available, using the default system linker.")
+    set(USE_LD_GOLD OFF)
+  endif()
 endif()
 
 # Add discord-rpc here