Document why we don't enable LTO on RelWithDebInfo (#1588)

Signed-off-by: Juan Cruz Viotti <[email protected]>

Author: jviotti

cmake/common/defaults.cmake

@@ -90,19 +90,24 @@ endif()
 # - https://gcc.gnu.org/onlinedocs/gccint/LTO-Overview.html
 # - https://llvm.org/docs/FatLTO.html
 
-if(SOURCEMETA_COMPILER_GCC AND CMAKE_BUILD_TYPE STREQUAL "Release" AND NOT BUILD_SHARED_LIBS)
-  message(STATUS "Enabling Fat LTO")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flto -ffat-lto-objects")
-  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -flto")
-  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -flto")
-endif()
+# Note we don't enable LTO on RelWithDebInfo, as it breaks debugging symbols
+# on at least AppleClang, making stepping through source code impossible.
+
+if(CMAKE_BUILD_TYPE STREQUAL "Release")
+  if(SOURCEMETA_COMPILER_GCC AND NOT BUILD_SHARED_LIBS)
+    message(STATUS "Enabling Fat LTO")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flto -ffat-lto-objects")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -flto")
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -flto")
+  endif()
 
-# TODO: Make this work on Linux on LLVM
-if(SOURCEMETA_COMPILER_LLVM AND CMAKE_BUILD_TYPE STREQUAL "Release" AND NOT BUILD_SHARED_LIBS AND APPLE)
-  message(STATUS "Enabling Fat LTO")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flto=full")
-  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -flto=full")
-  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -flto=full")
+  # TODO: Make this work on Linux on LLVM
+  if(SOURCEMETA_COMPILER_LLVM AND NOT BUILD_SHARED_LIBS AND APPLE)
+    message(STATUS "Enabling Fat LTO")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flto=full")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -flto=full")
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -flto=full")
+  endif()
 endif()
 
 # Attempt to enable SIMD (SSE/AVX/NEON)