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# - Use only needed imports from libraries
#
# Add the -Wl,--as-needed flag to the default linker flags on Linux
# in order to get only the minimal set of dependencies.
function (prepend var_name value)
# only add the prefix if it is not already at the beginning. this
# prevents the same string to be added at the same place every time
# we check for reconfiguration (e.g. "--as-needed" below)
string (LENGTH "${value}" _val_len)
string (LENGTH "${${var_name}}" _var_len)
if (NOT (${_var_len} LESS ${_val_len}))
string (SUBSTRING "${${var_name}}" 0 ${_val_len} _var_pre)
else (NOT (${_var_len} LESS ${_val_len}))
set (_var_pre)
endif (NOT (${_var_len} LESS ${_val_len}))
if (NOT ("${_var_pre}" STREQUAL "${value}"))
if (${var_name})
set (${var_name} "${value} ${${var_name}}" PARENT_SCOPE)
else (${var_name})
set (${var_name} "${value}")
endif (${var_name})
endif (NOT ("${_var_pre}" STREQUAL "${value}"))
endfunction (prepend var_name value)
option (ONLY_NEEDED_LIBRARIES "Instruct the linker to not use libraries which are unused" OFF)
# only ELF shared objects can be underlinked, and only GNU will accept
# these parameters; otherwise just leave it to the defaults
if ((CMAKE_CXX_PLATFORM_ID STREQUAL "Linux") AND CMAKE_COMPILER_IS_GNUCC AND ONLY_NEEDED_LIBRARIES)
# these are the modules whose probes will turn up incompatible
# flags on some systems
set (_maybe_underlinked
SuiteSparse
)
# check if any modules actually reported problems (by setting an
# appropriate linker flag)
set (_underlinked FALSE)
foreach (_module IN LISTS _maybe_underlinked)
if ("${${_module}_LINKER_FLAGS}" MATCHES "-Wl,--no-as-needed")
set (_underlinked TRUE)
endif ("${${_module}_LINKER_FLAGS}" MATCHES "-Wl,--no-as-needed")
endforeach (_module)
# if we didn't have any problems, then go ahead and add
if (NOT _underlinked)
prepend (CMAKE_EXE_LINKER_FLAGS "-Wl,--as-needed")
prepend (CMAKE_MODULE_LINKER_FLAGS "-Wl,--as-needed")
prepend (CMAKE_SHARED_LINKER_FLAGS "-Wl,--as-needed")
endif (NOT _underlinked)
endif ((CMAKE_CXX_PLATFORM_ID STREQUAL "Linux") AND CMAKE_COMPILER_IS_GNUCC AND ONLY_NEEDED_LIBRARIES)
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