On Darwin, pass LIBLTO_PATH to 'ar' and 'lipo' commands from CMake (#41243)

Author: kubamracek

cmake/modules/UnixCompileRules.cmake

@@ -11,3 +11,20 @@ set(CMAKE_C_ARCHIVE_FINISH "")
 set(CMAKE_CXX_ARCHIVE_CREATE "<CMAKE_AR> crs <TARGET> <LINK_FLAGS> <OBJECTS>")
 set(CMAKE_CXX_ARCHIVE_APPEND "<CMAKE_AR> qs <TARGET> <LINK_FLAGS> <OBJECTS>")
 set(CMAKE_CXX_ARCHIVE_FINISH "")
+
+# When archiving LTO-based .o files with ar/ranlib/libtool on Darwin, the tools
+# use libLTO.dylib to inspect the bitcode files. However, by default the
+# "host" libLTO.dylib is loaded, which might be too old and not understand our
+# just-built bitcode format. So let's instead ask ar/ranlib/libtool to use the
+# just-built libLTO.dylib from the toolchain that we're using to build.
+if(APPLE AND SWIFT_NATIVE_CLANG_TOOLS_PATH)
+  set(liblto_path "${SWIFT_NATIVE_CLANG_TOOLS_PATH}/../lib/libLTO.dylib")
+
+  set(CMAKE_C_ARCHIVE_CREATE "${CMAKE_COMMAND} -E env LIBLTO_PATH=${liblto_path} <CMAKE_AR> crs <TARGET> <LINK_FLAGS> <OBJECTS>")
+  set(CMAKE_C_ARCHIVE_APPEND "${CMAKE_COMMAND} -E env LIBLTO_PATH=${liblto_path} <CMAKE_AR> qs <TARGET> <LINK_FLAGS> <OBJECTS>")
+  set(CMAKE_C_ARCHIVE_FINISH "")
+
+  set(CMAKE_CXX_ARCHIVE_CREATE "${CMAKE_COMMAND} -E env LIBLTO_PATH=${liblto_path} <CMAKE_AR> crs <TARGET> <LINK_FLAGS> <OBJECTS>")
+  set(CMAKE_CXX_ARCHIVE_APPEND "${CMAKE_COMMAND} -E env LIBLTO_PATH=${liblto_path} <CMAKE_AR> qs <TARGET> <LINK_FLAGS> <OBJECTS>")
+  set(CMAKE_CXX_ARCHIVE_FINISH "")
+endif()

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -546,9 +546,20 @@ function(_add_swift_lipo_target)
     if(LIPO_CODESIGN)
       set(codesign_command COMMAND "codesign" "-f" "-s" "-" "${LIPO_OUTPUT}")
     endif()
+
+    set(lipo_lto_env)
+    # When lipo-ing LTO-based libraries with lipo on Darwin, the tool uses
+    # libLTO.dylib to inspect the bitcode files. However, by default the "host"
+    # libLTO.dylib is loaded, which might be too old and not understand the
+    # just-built bitcode format. Let's ask lipo to use the just-built
+    # libLTO.dylib from the toolchain that we're using to build.
+    if(APPLE AND SWIFT_NATIVE_CLANG_TOOLS_PATH)
+      set(lipo_lto_env "LIBLTO_PATH=${SWIFT_NATIVE_CLANG_TOOLS_PATH}/../lib/libLTO.dylib")
+    endif()
+
     # Use lipo to create the final binary.
     add_custom_command_target(unused_var
-        COMMAND "${SWIFT_LIPO}" "-create" "-output" "${LIPO_OUTPUT}" ${source_binaries}
+        COMMAND "${CMAKE_COMMAND}" "-E" "env" ${lipo_lto_env} "${SWIFT_LIPO}" "-create" "-output" "${LIPO_OUTPUT}" ${source_binaries}
         ${codesign_command}
         CUSTOM_TARGET_NAME "${LIPO_TARGET}"
         OUTPUT "${LIPO_OUTPUT}"