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CMake: Solve compilation error with pre-compiled libraries and new GCC-6

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Since version 6 G++ switched to C++11 by default, which breaks some logic
around WITH_CXX11 checks in out CMake files, leading to compilation errors.
This is easy to solve by explicitly enabling older C++ standard when C++11
was not explicitly enabled by CMake options.

However, G++-6 will also use new ABI by default even if older standard was
specified in the compiler options. This is being addressed by a special
define flag.

This tricks made it possible to use new G++-6 without need to recompile
any of pre-compiled libraries.

However, this might break compilation with existing system libraries, which
might already be using new ABI. We can't address this automatically, so
now we simply default WITH_C11 and WITH_CXX11 options to whatever defaults
of the current compiler are. This means, for G++-6 we'll set WITH_CXX11 to
truth. This should make linking with system libraries working just fine,
but to make pre-compiled libraries we still might need to disable CXX11.

This should work fine work for a new environments with G++-6 and install_deps
script run from scratch there, because C++ standard will be the same for
both Blender dependencies and Blender itself.
This commit is contained in:
Sergey Sharybin
2016-05-22 13:41:55 +02:00
parent e21af38f69
commit 6115267a84
2 changed files with 31 additions and 3 deletions
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24
CMakeLists.txt
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@@ -478,9 +478,19 @@ if(WIN32)
endif()
# Experimental support of C11 and C++11
option(WITH_C11 "Build with C11 standard enabled, for development use only!" OFF)
#
# We default options to whatever default standard in the current compiler.
if(CMAKE_COMPILER_IS_GNUCC AND (NOT "${CMAKE_C_COMPILER_VERSION}" VERSION_LESS "6.0") AND (NOT WITH_CXX11))
set(_c11_init ON)
set(_cxx11_init ON)
else()
set(_c11_init OFF)
set(_cxx11_init OFF)
endif()
option(WITH_C11 "Build with C11 standard enabled, for development use only!" ${_c11_init})
mark_as_advanced(WITH_C11)
option(WITH_CXX11 "Build with C++11 standard enabled, for development use only!" OFF)
option(WITH_CXX11 "Build with C++11 standard enabled, for development use only!" ${_cxx11_init})
mark_as_advanced(WITH_CXX11)
# Dependency graph
@@ -3024,12 +3034,22 @@ endif()
if(WITH_CXX11)
if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID MATCHES "Clang")
# TODO(sergey): Do we want c++11 or gnu-c++11 here?
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
elseif(MSVC12)
# Nothing special is needed, C++11 features are available by default.
else()
message(FATAL_ERROR "Compiler ${CMAKE_C_COMPILER_ID} is not supported for C++11 build yet")
endif()
else()
# GCC-6 switched to C++11 by default, which would break linking with existing libraries
# by default. So we explicitly disable C++11 for a new GCC so no linking issues happens.
if(CMAKE_COMPILER_IS_GNUCC AND (NOT "${CMAKE_C_COMPILER_VERSION}" VERSION_LESS "6.0"))
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++98")
# We also disable any of C++11 ABI from usage, so we wouldn't even try to
# link to stuff from std::__cxx11 namespace.
add_definitions("-D_GLIBCXX_USE_CXX11_ABI=0")
endif()
endif()
# Visual Studio has all standards it supports available by default