Enable whole-module-optimization in release builds

Author: jmschonfeld

CMakeLists.txt

@@ -112,6 +112,13 @@ if(CMAKE_SYSTEM_NAME STREQUAL "WASI")
         "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xcc -D_WASI_EMULATED_MMAN>")
 endif()
 
+# Enable whole module optimization for release builds & incremental for debug builds
+if(POLICY CMP0157)
+    set(CMAKE_Swift_COMPILATION_MODE "$<IF:$<CONFIG:Release>,wholemodule,incremental>")
+else()
+    add_compile_options($<$<AND:$<COMPILE_LANGUAGE:Swift>,$<IF:$<CONFIG:Release>>>:-wmo>)
+endif()
+
 include(GNUInstallDirs)
 include(SwiftFoundationSwiftSupport)