From 6e259170011cd2fbac069b9d4ff83b42445a96cc Mon Sep 17 00:00:00 2001
From: Eric <eric@efcs.ca>
Date: Mon, 29 Aug 2016 12:43:30 -0600
Subject: [PATCH] Add -DBENCHMARK_USE_LIBCXX:BOOL=<value> option. (#280)

* Add BENCHMARK_USE_LIBCXX option.

* Add comments

* re-add zero null pointer warning
---
 CMakeLists.txt              | 23 ++++++++++++++++++++++-
 cmake/CXXFeatureCheck.cmake |  4 +++-
 src/CMakeLists.txt          |  8 ++++++--
 test/CMakeLists.txt         |  9 ++++++++-
 4 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a1251e74..1ef83007 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,6 +12,7 @@ endforeach()
 
 option(BENCHMARK_ENABLE_TESTING "Enable testing of the benchmark library." ON)
 option(BENCHMARK_ENABLE_LTO "Enable link time optimisation of the benchmark library." OFF)
+option(BENCHMARK_USE_LIBCXX "Build and test using libc++ as the standard library." OFF)
 # Make sure we can import out CMake functions
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 
@@ -78,8 +79,10 @@ else()
   add_cxx_compiler_flag(-pedantic-errors)
   add_cxx_compiler_flag(-Wshorten-64-to-32)
   add_cxx_compiler_flag(-Wfloat-equal)
-  add_cxx_compiler_flag(-Wzero-as-null-pointer-constant)
   add_cxx_compiler_flag(-fstrict-aliasing)
+  if (NOT BENCHMARK_USE_LIBCXX)
+    add_cxx_compiler_flag(-Wzero-as-null-pointer-constant)
+  endif()
   if (HAVE_CXX_FLAG_FSTRICT_ALIASING)
     add_cxx_compiler_flag(-Wstrict-aliasing)
   endif()
@@ -126,6 +129,24 @@ else()
   add_cxx_compiler_flag(--coverage COVERAGE)
 endif()
 
+if (BENCHMARK_USE_LIBCXX)
+  if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+    add_cxx_compiler_flag(-stdlib=libc++)
+  elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" OR
+          "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Intel")
+    add_cxx_compiler_flag(-nostdinc++)
+    message("libc++ header path must be manually specified using CMAKE_CXX_FLAGS")
+    # Adding -nodefaultlibs directly to CMAKE_<TYPE>_LINKER_FLAGS will break
+    # configuration checks such as 'find_package(Threads)'
+    list(APPEND BENCHMARK_CXX_LINKER_FLAGS -nodefaultlibs)
+    # -lc++ cannot be added directly to CMAKE_<TYPE>_LINKER_FLAGS because
+    # linker flags appear before all linker inputs and -lc++ must appear after.
+    list(APPEND BENCHMARK_CXX_LIBRARIES c++)
+  else()
+    message(FATAL "-DBENCHMARK_USE_LIBCXX:BOOL=ON is not supported for compiler")
+  endif()
+endif(BENCHMARK_USE_LIBCXX)
+
 # C++ feature checks
 cxx_feature_check(STD_REGEX)
 cxx_feature_check(GNU_POSIX_REGEX)
diff --git a/cmake/CXXFeatureCheck.cmake b/cmake/CXXFeatureCheck.cmake
index 3059024d..b106f32b 100644
--- a/cmake/CXXFeatureCheck.cmake
+++ b/cmake/CXXFeatureCheck.cmake
@@ -26,7 +26,9 @@ function(cxx_feature_check FILE)
   endif()
   message("-- Performing Test ${FEATURE}")
   try_run(RUN_${FEATURE} COMPILE_${FEATURE}
-          ${CMAKE_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/${FILE}.cpp)
+          ${CMAKE_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/${FILE}.cpp
+          CMAKE_FLAGS ${BENCHMARK_CXX_LINKER_FLAGS}
+          LINK_LIBRARIES ${BENCHMARK_CXX_LIBRARIES})
   if(RUN_${FEATURE} EQUAL 0)
     message("-- Performing Test ${FEATURE} -- success")
     set(HAVE_${VAR} 1 CACHE INTERNAL "Feature test for ${FILE}" PARENT_SCOPE)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 6dab64b7..a65723b0 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,6 +1,11 @@
 # Allow the source files to find headers in src/
 include_directories(${PROJECT_SOURCE_DIR}/src)
 
+if (DEFINED BENCHMARK_CXX_LINKER_FLAGS)
+  list(APPEND CMAKE_SHARED_LINKER_FLAGS ${BENCHMARK_CXX_LINKER_FLAGS})
+  list(APPEND CMAKE_MODULE_LINKER_FLAGS ${BENCHMARK_CXX_LINKER_FLAGS})
+endif()
+
 # Define the source files
 set(SOURCE_FILES "benchmark.cc" "colorprint.cc" "commandlineflags.cc"
                  "console_reporter.cc" "csv_reporter.cc" "json_reporter.cc"
@@ -19,7 +24,6 @@ endif()
 
 add_library(benchmark ${SOURCE_FILES} ${RE_FILES})
 
-
 set_target_properties(benchmark PROPERTIES
   OUTPUT_NAME "benchmark"
   VERSION ${GENERIC_LIB_VERSION}
@@ -27,7 +31,7 @@ set_target_properties(benchmark PROPERTIES
 )
 
 # Link threads.
-target_link_libraries(benchmark ${CMAKE_THREAD_LIBS_INIT})
+target_link_libraries(benchmark  ${BENCHMARK_CXX_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT})
 
 # We need extra libraries on Windows
 if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index acfb48dd..dd77744c 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -2,6 +2,12 @@
 
 find_package(Threads REQUIRED)
 
+# NOTE: These flags must be added after find_package(Threads REQUIRED) otherwise
+# they will break the configuration check.
+if (DEFINED BENCHMARK_CXX_LINKER_FLAGS)
+  list(APPEND CMAKE_EXE_LINKER_FLAGS ${BENCHMARK_CXX_LINKER_FLAGS})
+endif()
+
 add_library(output_test_helper STATIC output_test_helper.cc)
 
 macro(compile_benchmark_test name)
@@ -12,7 +18,8 @@ endmacro(compile_benchmark_test)
 
 macro(compile_output_test name)
   add_executable(${name} "${name}.cc")
-  target_link_libraries(${name} output_test_helper benchmark ${CMAKE_THREAD_LIBS_INIT})
+  target_link_libraries(${name} output_test_helper benchmark
+          ${BENCHMARK_CXX_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT})
 endmacro(compile_output_test)