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added: (advanced) support for LTO in buildsystem
while cmake has a generic CMAKE_INTERPROCEDURAL_OPTIMIZATION flag this is problematic since it uses all cores for each linker job, overwhelming the system when there are many linking stages. so we add our own, mostly "borrowed" from opm-common and simplified, with support for setting the number of jobs and for using LTO cache where available. - -DIFEM_USE_LTO to enable - -DIFEM_LTO_JOBS=x to set number of linker optimization job - -DIFEM_LTO_CONFIGURATION_TYPES=xx to enable for a configuration (defaults to Release and RelWithDebubInfo) - -DIFEM_LTO_CACHE_POLICY to override default lto cache policies
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‎CMakeLists.txt‎

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@@ -26,6 +26,7 @@ list(APPEND CMAKE_MODULE_PATH
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include(IFEMOptions)
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include(IFEMBuildTypes)
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include(IFEMLTO)
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add_library(IFEM)
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@@ -38,6 +39,7 @@ set_target_properties(
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SOVERSION
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${IFEM_ABI_VERSION}
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)
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ifem_lto(TARGET IFEM)
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target_compile_definitions(IFEM PUBLIC $<$<CONFIG:Debug>:INDEX_CHECK=2>)
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if(VERBOSE_DEBUG GREATER 0)
@@ -718,6 +720,7 @@ install(
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cmake/IFEMAddTargets.cmake
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cmake/IFEMDoxy.cmake
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cmake/IFEMFindDependencies.cmake
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cmake/IFEMLTO.cmake
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cmake/IFEMOptionsDownstream.cmake
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cmake/IFEMTesting.cmake
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cmake/Modules/FindARPACK.cmake

‎cmake/IFEMAddTargets.cmake‎

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@@ -38,6 +38,7 @@ function(ifem_add_library)
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ARCHIVE_OUTPUT_DIRECTORY
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${CMAKE_BINARY_DIR}/lib
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)
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ifem_lto(TARGET ${PARAM_NAME})
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ifem_add_sca_tests(TARGET ${PARAM_NAME})
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endfunction()
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@@ -68,6 +69,7 @@ function(ifem_add_application)
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RUNTIME_OUTPUT_DIRECTORY
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${CMAKE_BINARY_DIR}/bin
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)
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ifem_lto(TARGET ${PARAM_NAME})
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ifem_add_sca_tests(TARGET ${PARAM_NAME})
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list(APPEND TEST_APPS ${PARAM_NAME})
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set(TEST_APPS ${TEST_APPS} PARENT_SCOPE)

‎cmake/IFEMLTO.cmake‎

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@@ -0,0 +1,134 @@
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include(CheckIPOSupported)
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include(TestCXXAcceptsFlag)
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# ------------------------------------------------------------------------------
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# ifem_lto
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#
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# Configure link-time optimization (IPO) for a target.
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#
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# This function enables LTO (Link Time Optimization) on the specified target.
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# It has extended interfaces for GCC and Clang settings.
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#
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# Enablement is controlled using the IFEM_USE_LTO option.
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#
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# Incremental cache directories are automatically managed under:
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# ${CMAKE_BINARY_DIR}/LTOCache/<config>
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#
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# Usage:
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#
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# ifem_ipo(
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# TARGET <target>
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# [CONFIGURATION_TYPES <config1;config2;...>]
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# )
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#
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# Arguments:
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# TARGET (required) Target to which optimization will be applied.
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# CONFIGURATION_TYPES (optional) List of configuration names (e.g. Release).
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# If omitted, the default list from:
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# IFEM_LTO_CONFIGURATION_TYPES
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# is used.
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#
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# Cache Variables:
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# IFEM_LTO_JOBS (e.g. 1, 8)
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# IFEM_LTO_CACHE_POLICY (e.g. "prune_after=604800")
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# IFEM_LTO_CONFIGURATION_TYPES (e.g. "Release;RelWithDebInfo")
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#
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# ------------------------------------------------------------------------------
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set(IFEM_LTO_CONFIGURATION_TYPES "Release;RelWithDebInfo" CACHE
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STRING "Default configuration types to apply interprocedural optimization.")
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set(IFEM_LTO_JOBS 1 CACHE STRING "Default interprocedural optimization jobs. Set to 'auto' to use all cores")
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set(IFEM_LTO_CACHE_POLICY "" CACHE STRING "Default interprocedural optimization cache policy.")
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mark_as_advanced(IFEM_LTO_CACHE_POLICY)
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mark_as_advanced(IFEM_LTO_CONFIGURATION_TYPES)
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# define possible values for LTO (order matters: first one in the list is used as default type)
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set(ifem_ipo_types)
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check_ipo_supported(LANGUAGES C CXX RESULT ipo_supported)
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if(IFEM_USE_LTO AND NOT ipo_supported)
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message(STATUS "Link-time optimization not supported")
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set(IFEM_USE_LTO OFF)
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endif()
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if(IFEM_USE_LTO)
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message(STATUS "Link-time optimization enabled")
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endif()
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function(ifem_lto)
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if(NOT IFEM_USE_LTO)
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return()
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endif()
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cmake_parse_arguments(PARAM "" "TARGET" "CONFIGURATION_TYPES" ${ARGN})
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# if not set, use the default configuration types
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if(NOT PARAM_CONFIGURATION_TYPES)
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set(PARAM_CONFIGURATION_TYPES ${IFEM_LTO_CONFIGURATION_TYPES})
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endif()
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foreach(config ${PARAM_CONFIGURATION_TYPES})
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if(CMAKE_CONFIGURATION_TYPES MATCHES ${config} OR CMAKE_BUILD_TYPE MATCHES ${config})
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set(LTO_CACHE_PATH ${CMAKE_BINARY_DIR}/LTOCache/${config})
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if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
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# https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/Optimize-Options.html
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target_compile_options(${PARAM_TARGET} PRIVATE $<$<CONFIG:${config}>:-flto=${IFEM_LTO_JOBS}>)
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target_link_options(${PARAM_TARGET} INTERFACE $<$<CONFIG:${config}>:-flto=${IFEM_LTO_JOBS}>)
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if(CMAKE_CXX_COMPILER_VERSION GREATER_EQUAL 15.0.0)
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# use incremental LTO https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Optimize-Options.html
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target_compile_options(${PARAM_TARGET} PRIVATE $<$<CONFIG:${config}>:-flto-incremental=${LTO_CACHE_PATH}>)
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target_link_options(${PARAM_TARGET} INTERFACE $<$<CONFIG:${config}>:-flto-incremental=${LTO_CACHE_PATH}>)
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# Configure cache directory
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file(MAKE_DIRECTORY ${LTO_CACHE_PATH})
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set_property(DIRECTORY APPEND PROPERTY ADDITIONAL_CLEAN_FILES ${LTO_CACHE_PATH})
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endif()
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elseif(CMAKE_CXX_COMPILER_ID STREQUAL Clang)
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# Use ThinLTO and reuse cache (see https://releases.llvm.org/20.1.0/tools/clang/docs/ThinLTO.html)
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if(${CMAKE_CXX_COMPILER_LINKER_ID} MATCHES "GNU")
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message(FATAL_ERROR "Cannot use ThinLTO with BFD linker")
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endif()
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target_compile_options(${PARAM_TARGET} PRIVATE $<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CONFIG:${config}>>:-flto=thin>)
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target_link_options(${PARAM_TARGET} INTERFACE $<$<CONFIG:${config}>:-flto=thin>)
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# Configure cache directory
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file(MAKE_DIRECTORY ${LTO_CACHE_PATH})
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set_property(DIRECTORY APPEND PROPERTY ADDITIONAL_CLEAN_FILES ${LTO_CACHE_PATH})
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# Parallel and cache options are linker dependent
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if(${CMAKE_CXX_COMPILER_LINKER_ID} MATCHES "LLD")
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target_link_options(${PARAM_TARGET} INTERFACE
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$<$<CONFIG:${config}>:LINKER:--thinlto-jobs=${IFEM_LTO_JOBS}>
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$<$<CONFIG:${config}>:LINKER:--thinlto-cache-dir=${LTO_CACHE_PATH}>
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)
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if(IFEM_LTO_CACHE_POLICY)
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target_link_options(${PARAM_TARGET} INTERFACE
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$<$<CONFIG:${config}>:LINKER:--thinlto-cache-policy=${IFEM_LTO_CACHE_POLICY}>
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)
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endif()
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elseif(${CMAKE_CXX_COMPILER_LINKER_ID} MATCHES "GNU|GNUgold|MOLD")
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target_link_options(${PARAM_TARGET} INTERFACE
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$<$<CONFIG:${config}>:LINKER:-plugin-opt,jobs=${IFEM_LTO_JOBS}>
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$<$<CONFIG:${config}>:LINKER:-plugin-opt,cache-dir=${LTO_CACHE_PATH}>
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)
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if(IFEM_LTO_CACHE_POLICY)
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target_link_options(${PARAM_TARGET} INTERFACE
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$<$<CONFIG:${config}>:LINKER:-plugin-opt,cache-policy=${IFEM_LTO_CACHE_POLICY}>
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)
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endif()
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elseif(${CMAKE_CXX_COMPILER_LINKER_ID} MATCHES "AppleClang")
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target_link_options(${PARAM_TARGET} INTERFACE
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$<$<CONFIG:${config}>:LINKER:-mllvm,-threads=${IFEM_LTO_JOBS}>
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$<$<CONFIG:${config}>:LINKER:-cache_path_lto,${LTO_CACHE_PATH}>
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)
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else()
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message(DEBUG "LTO for Clang is supported, but linker type '${CMAKE_CXX_COMPILER_LINKER_ID}' is unrecognized. Skip adding parallelism or cache flags.")
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endif()
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endif()
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endif()
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endforeach()
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endfunction()

‎cmake/IFEMOptions.cmake‎

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@@ -15,6 +15,7 @@ option(IFEM_USE_UMFPACK "Compile with UMFPACK support?" ON)
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option(IFEM_USE_CEREAL "Compile with cereal support?" ON)
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option(IFEM_USE_ZOLTAN "Compile with zoltan support?" OFF)
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option(IFEM_USE_TRACY "Enable tracer profiler?" OFF)
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option(IFEM_USE_LTO "Enable link-time optimizoation?" OFF)
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set(IFEM_USE_SPR "OFF" CACHE STRING "Compile with SPR support?")
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set_property(CACHE IFEM_USE_SPR PROPERTY STRINGS ON I32 I64 OFF)

‎cmake/IFEMSetupDependencies.cmake‎

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@@ -12,6 +12,8 @@ target_link_libraries(IFEM PUBLIC
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${CMAKE_Fortran_IMPLICIT_LINK_LIBRARIES}
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)
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target_link_directories(IFEM PUBLIC ${CMAKE_Fortran_IMPLICIT_LINK_DIRECTORIES})
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if(IFEM_USE_SUPERLU OR IFEM_USE_SUPERLU_MT)
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if(IFEM_USE_SUPERLU_MT AND TARGET SuperLU::SuperLUMT)
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target_link_libraries(IFEM PUBLIC SuperLU::SuperLUMT)

‎cmake/Templates/IFEMConfig-install.cmake.in‎

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@@ -26,6 +26,7 @@ list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR})
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMFindDependencies.cmake")
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMOptionsDownstream.cmake")
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMTargets.cmake")
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMLTO.cmake")
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMAddTargets.cmake")
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMTesting.cmake")
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMDoxy.cmake")

‎cmake/Templates/IFEMConfig.cmake.in‎

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@@ -21,6 +21,7 @@ set(IFEM_PATH @IFEM_PATH@)
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list(APPEND CMAKE_MODULE_PATH ${IFEM_PATH}/cmake ${IFEM_PATH}/cmake/Modules)
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include(IFEMSetupVariables)
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include(IFEMFindDependencies)
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include(IFEMLTO)
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include(IFEMAddTargets)
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include(IFEMOptionsDownstream)
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include("${CMAKE_CURRENT_LIST_DIR}/IFEMTargets.cmake")

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