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# This module enables precompiled headers. To use:
#
# include(pch)
# add_pch(<path_to_system_header_list> <build_target>) # Optional
#
# For example:
#
# include(pch)
# add_pch(pch/pch_sys_headers.hh mylibrary)
#
# pch_sys_headers.hh must contain a list of #includes for system headers
# that should be precompiled, such as
#
# #include<vector>
# #include<iostream>
# ...
#
# Due to various limitations this implementation only works
# with C++. It is also strongly recommended that the suffix
# of your pch file should be .hh rather than .h.
function(get_gcc_flags target_name)
# CMake does not provide an easy way to get all compiler switches,
# so this function is a fishing expedition to get them.
# http://public.kitware.com/Bug/view.php?id=1260
if(CMAKE_CXX_COMPILER_ARG1)
set(compile_args ${CMAKE_CXX_COMPILER_ARG1})
else()
set(compile_args "")
endif()
if(CMAKE_CXX_COMPILER_ARG2)
list(APPEND compile_args ${CMAKE_CXX_COMPILER_ARG2})
endif()
list(APPEND compile_args ${CMAKE_CXX_FLAGS})
string(TOUPPER "${CMAKE_BUILD_TYPE}" buildtype_name)
if(CMAKE_CXX_FLAGS_${buildtype_name})
list(APPEND compile_args ${CMAKE_CXX_FLAGS_${buildtype_name}})
endif()
get_directory_property(dir_inc INCLUDE_DIRECTORIES)
foreach(item ${dir_inc})
LIST(APPEND compile_args "-I" ${item})
endforeach()
get_directory_property(dir_defs COMPILE_DEFINITIONS)
foreach(item ${dir_defs})
list(APPEND compile_args -D${item})
endforeach()
get_directory_property(dir_buildtype_defs COMPILE_DEFINITIONS_${buildtype_name})
foreach(item ${dir_buildtype_defs})
list(APPEND compile_args -D${item})
endforeach()
get_directory_property(buildtype_defs COMPILE_DEFINITIONS_${buildtype_name})
foreach(item ${buildtype_defs})
list(APPEND compile_args -D${item})
endforeach()
get_target_property(target_type ${target_name} TYPE)
if(${target_type} STREQUAL SHARED_LIBRARY)
list(APPEND compile_args ${CMAKE_CXX_COMPILE_OPTIONS_PIC})
endif()
get_target_property(target_defs ${target_name} COMPILE_DEFINITIONS)
if(target_defs)
foreach(item ${target_defs})
list(APPEND compile_args -D${item})
endforeach()
endif()
get_target_property(target_buildtype_defs ${target_name} COMPILE_DEFINITIONS_${buildtype_name})
if(target_buildtype_defs)
foreach(item ${target_buildtype_defs})
list(APPEND compile_args -D${item})
endforeach()
endif()
get_target_property(target_flags ${target_name} COMPILE_FLAGS)
if(target_flags)
list(APPEND compile_args ${target_flags})
endif()
set(compile_args ${compile_args} PARENT_SCOPE)
#message(STATUS ${compile_args})
endfunction()
function(add_pch_linux header_filename target_name pch_suffix)
set(gch_target_name "${target_name}_pch")
get_filename_component(header_basename ${header_filename} NAME)
set(gch_filename "${CMAKE_CURRENT_BINARY_DIR}/${header_basename}.${pch_suffix}")
get_gcc_flags(${target_name}) # Sets compile_args in this scope. It's even better than Intercal's COME FROM!
#message(STATUS ${compile_args})
list(APPEND compile_args -c ${CMAKE_CURRENT_SOURCE_DIR}/${header_filename} -o ${gch_filename})
separate_arguments(compile_args)
add_custom_command(OUTPUT ${gch_filename}
COMMAND ${CMAKE_CXX_COMPILER} ${compile_args}
DEPENDS ${header_filename})
add_custom_target(${gch_target_name} DEPENDS ${gch_filename})
add_dependencies(${target_name} ${gch_target_name})
# Add the PCH to every source file's include list.
# This is the only way that is supported by both GCC and Clang.
set_property(TARGET ${target_name} APPEND_STRING PROPERTY COMPILE_FLAGS " -include ${header_basename}")
set_property(TARGET ${target_name} APPEND_STRING PROPERTY COMPILE_FLAGS " -Winvalid-pch")
set_property(TARGET ${target_name} APPEND PROPERTY INCLUDE_DIRECTORIES ${CMAKE_CURRENT_BINARY_DIR})
endfunction()
include(CheckCXXSourceCompiles)
CHECK_CXX_SOURCE_COMPILES("#ifdef __clang__\n#else\n#error \"Not clang.\"\n#endif\nint main(int argc, char **argv) { return 0; }" IS_CLANG)
if(UNIX)
if(NOT APPLE)
option(use_pch "Use precompiled headers." TRUE)
endif()
endif()
if(use_pch)
message(STATUS "Using precompiled headers.")
if(IS_CLANG)
set(precompiled_header_extension pch)
else()
set(precompiled_header_extension gch)
endif()
macro(add_pch _header_filename _target_name)
add_pch_linux(${_header_filename} ${_target_name} ${precompiled_header_extension})
endmacro()
else()
message(STATUS "Not using precompiled headers.")
macro(add_pch _header_filename _target_name)
endmacro()
endif()
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