[CMake] Revert r200695 and fix the problem with missing -fno-function-sections in a different way.

llvm-svn: 200745

1 files changed, 12 insertions, 10 deletions

diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 8e4b6bbdafd..b40103ca186 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -335,23 +335,25 @@ if (UNIX AND
   append("-fcolor-diagnostics" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 endif()
 
-# Clang prior to 3.5 ignored -fno-function-sections.
-# It's pretty hard to test directly, so we rely on the version number.
-if( ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang") AND (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.5) )
-  set(LLVM_COMPILER_HAS_BROKEN_FNO_FUNCTION_SECTIONS ON)
-endif()
-
 # Add flags for add_dead_strip().
 # FIXME: With MSVS, consider compiling with /Gy and linking with /OPT:REF?
 # But MinSizeRel seems to add that automatically, so maybe disable these
 # flags instead if LLVM_NO_DEAD_STRIP is set.
 if(NOT CYGWIN AND NOT WIN32)
   if(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
-    # Don't add -ffunction-section if it can be disabled with -fno-function-sections.
-    # Doing so will break sanitizers.
-    if (NOT LLVM_COMPILER_HAS_BROKEN_FNO_FUNCTION_SECTIONS)
-      append("-ffunction-sections -fdata-sections" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+    check_c_compiler_flag("-Werror -fno-function-sections" C_SUPPORTS_FNO_FUNCTION_SECTIONS)
+    if (C_SUPPORTS_FNO_FUNCTION_SECTIONS)
+      # Don't add -ffunction-section if it can be disabled with -fno-function-sections.
+      # Doing so will break sanitizers.
+      check_c_compiler_flag("-Werror -ffunction-sections" C_SUPPORTS_FFUNCTION_SECTIONS)
+      check_cxx_compiler_flag("-Werror -ffunction-sections" CXX_SUPPORTS_FFUNCTION_SECTIONS)
+      append_if(C_SUPPORTS_FFUNCTION_SECTIONS "-ffunction-sections" CMAKE_C_FLAGS)
+      append_if(CXX_SUPPORTS_FFUNCTION_SECTIONS "-ffunction-sections" CMAKE_CXX_FLAGS)
     endif()
+    check_c_compiler_flag("-Werror -fdata-sections" C_SUPPORTS_FDATA_SECTIONS)
+    check_cxx_compiler_flag("-Werror -fdata-sections" CXX_SUPPORTS_FDATA_SECTIONS)
+    append_if(C_SUPPORTS_FDATA_SECTIONS "-fdata-sections" CMAKE_C_FLAGS)
+    append_if(CXX_SUPPORTS_FDATA_SECTIONS "-fdata-sections" CMAKE_CXX_FLAGS)
   endif()
 endif()