From 4209d418d6fe24b244ef681a12df426ba9aa33e3 Mon Sep 17 00:00:00 2001
From: Ben Barham <ben_barham@apple.com>
Date: Mon, 22 May 2023 17:51:49 -0700
Subject: [PATCH] [CMake] Use WMO for release builds

This has a significant (5x) speed up when running our performance tests
on eg. apple/swift-docc.

(cherry picked from commit d9d09e8cd55933d8f5761349569477636989d4f7)
---
 cmake/modules/AddSwiftHostLibrary.cmake | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/cmake/modules/AddSwiftHostLibrary.cmake b/cmake/modules/AddSwiftHostLibrary.cmake
index 11acde9f52d..4ec93305bf1 100644
--- a/cmake/modules/AddSwiftHostLibrary.cmake
+++ b/cmake/modules/AddSwiftHostLibrary.cmake
@@ -56,6 +56,13 @@ function(add_swift_host_library name)
       -emit-module-interface-path;${module_interface_file}
       >)
 
+  if(NOT CMAKE_BUILD_TYPE STREQUAL "Debug")
+    target_compile_options(${name} PRIVATE
+        $<$<COMPILE_LANGUAGE:Swift>:
+        -wmo
+        >)
+  endif()
+
   # NOTE: workaround for CMake not setting up include flags yet
   set_target_properties(${name} PROPERTIES
     INTERFACE_INCLUDE_DIRECTORIES ${module_dir}