CMakeLists.txt BENCHMARK_BUILD_32_BITS fails with MSVC

[ghost]

CMakeLists.txt has an option BENCHMARK_BUILD_32_BITS. This works when gcc is used, but it fails with MSVC. In fact this option tries to add -m32 to the compiler options, and this is gcc-specific and doesn't work with MSVC.

With MSVC this option doesn't really make sense, because the CMake MSVC generator determines whether the build is 32-bit or 64-bit. An MSVC user probably doesn't want or expect that setting BENCHMARK_BUILD_32_BITS would make the build fail. Therefore, I propose that BENCHMARK_BUILD_32_BITS be ignored when using MSVC. Doing this is a trivial change to CMakeLists.txt, moving the -m32 stuff so that it is not used with MSVC.

Here's a diff:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4265a6c..74fe2ea 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -37,10 +37,6 @@ include(CheckCXXCompilerFlag)
include(AddCXXCompilerFlag)
include(CXXFeatureCheck)

-if (BENCHMARK_BUILD_32_BITS)

• add_required_cxx_compiler_flag(-m32)
  -endif()

if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")

Turn compiler warnings up to 11

string(REGEX REPLACE "[-/]W[1-4]" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
@@ -72,6 +68,10 @@ if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
set(CMAKE_EXE_LINKER_FLAGS_MINSIZEREL "${CMAKE_EXE_LINKER_FLAGS_MINSIZEREL} /LTCG")
endif()
else()

• if (BENCHMARK_BUILD_32_BITS)
• add_required_cxx_compiler_flag(-m32)
• endif()

• Try and enable C++11. Don't use C++14 because it doesn't work in some

  configurations.

  add_cxx_compiler_flag(-std=c++11)

[dmah42]

sgtm. PR welcome :)