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CMake: AMReX::Flags_FASTMATH Interface Helper Target (#4591)
## Summary This PR _changes no defaults_. It just refactors #4545 a bit further prior to adding the option `AMReX_FASTMATH` in a first AMReX release, providing a better internal implementation and a user-friendly helper target (fully optional). Add an interface target for the fast-math flags. This makes it easier to re-use them downstream when AMReX is pre-compiled w/o fast-math (default in all of our current package managers), but the main code wants to still use fast-math on the side of the application code. ## Additional background Follow-up to #4545, see comment #4545 (comment)
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‎Docs/sphinx_documentation/source/BuildingAMReX.rst‎

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@@ -443,7 +443,7 @@ The list of available options is reported in the :ref:`table <tab:cmakevar>` bel
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+------------------------------+-------------------------------------------------+-------------------------+-----------------------+
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| AMReX_BUILD_SHARED_LIBS | Build as shared C++ library | NO (unless xSDK) | YES, NO |
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+------------------------------+-------------------------------------------------+-------------------------+-----------------------+
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| AMReX_FASTMATH | Enable fast-math optimizations | NO (CPU), YES (CUDA) | YES, NO |
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| AMReX_FASTMATH | Enable fast-math optimizations | NO (CUDA is ON) | YES, NO |
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+------------------------------+-------------------------------------------------+-------------------------+-----------------------+
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| AMReX_FORTRAN | Enable Fortran language | NO | YES, NO |
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+------------------------------+-------------------------------------------------+-------------------------+-----------------------+

‎Src/CMakeLists.txt‎

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Original file line numberDiff line numberDiff line change
@@ -79,6 +79,10 @@ foreach(D IN LISTS AMReX_SPACEDIM)
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)
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endif ()
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82+
if (AMReX_FASTMATH)
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target_link_libraries(amrex_${D}d PUBLIC AMReX::Flags_FASTMATH)
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endif ()
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if (AMReX_FPE)
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target_link_libraries(amrex_${D}d
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PUBLIC

‎Tools/CMake/AMReXFlagsTargets.cmake‎

Lines changed: 36 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,7 @@
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#
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# Flags_CXX --> Optional flags for C++ code
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# Flags_Fortran --> Optional flags for Fortran code
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# Flags_FASTMATH --> Optional flags for fast-math (floating-point)
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# Flags_FPE --> Floating-Point Exception flags for both C++ and Fortran
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# Flags_INLINE --> Optional flags for inlining
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#
@@ -21,15 +22,15 @@ include_guard(GLOBAL)
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#
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# for every combination of
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#
24-
# <lang> = cxx,fortran
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# <id> = gnu,intel,pgi,cray,clang,appleclang,intelllvm,msvc
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# <lang> = cxx,fortran,cuda
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# <id> = gnu,intel,pgi,cray,clang,appleclang,crayclang,ibmclang,intelllvm,msvc,nvidia,nvhpc,xlclang
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#
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if (CMAKE_VERSION VERSION_LESS 3.20)
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foreach (_language CXX Fortran )
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foreach (_language CXX Fortran CUDA )
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set(_comp_lang "$<COMPILE_LANGUAGE:${_language}>")
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string(TOLOWER "${_language}" _lang)
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32-
foreach (_comp GNU Intel PGI Cray Clang AppleClang IntelLLVM MSVC )
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foreach (_comp GNU Intel PGI Cray Clang AppleClang CrayClang IBMClang IntelLLVM MSVC NVIDIA NVHPC XLClang )
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string(TOLOWER "${_comp}" _id)
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# Define variables
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set(_comp_id "$<${_language}_COMPILER_ID:${_comp}>")
@@ -44,10 +45,10 @@ if (CMAKE_VERSION VERSION_LESS 3.20)
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unset(_lang)
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endforeach ()
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else ()
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foreach (_language CXX Fortran )
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foreach (_language CXX Fortran CUDA )
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string(TOLOWER "${_language}" _lang)
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foreach (_comp GNU Intel PGI Cray Clang AppleClang IntelLLVM MSVC )
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foreach (_comp GNU Intel PGI Cray Clang AppleClang CrayClang IBMClang IntelLLVM MSVC NVIDIA NVHPC XLClang )
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string(TOLOWER "${_comp}" _id)
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# Define variables
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set(_${_lang}_${_id} "$<COMPILE_LANG_AND_ID:${_language},${_comp}>")
@@ -127,6 +128,35 @@ target_compile_options( Flags_Fortran
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)
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#
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# Fast-Math (for floating point)
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#
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add_library(Flags_FASTMATH INTERFACE)
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add_library(AMReX::Flags_FASTMATH ALIAS Flags_FASTMATH)
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target_compile_options( Flags_FASTMATH
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INTERFACE
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$<${_cuda_nvidia}:--use_fast_math>
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$<${_cuda_nvhpc}:-fast>
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$<${_fortran_gnu}:-ffast-math>
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$<${_cxx_gnu}:-ffast-math>
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$<${_fortran_intel}:-ffast-math>
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$<${_cxx_intel}:-ffast-math>
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$<${_fortran_pgi}:-ffast-math>
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$<${_cxx_pgi}:-ffast-math>
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$<${_fortran_cray}:-ffast-math>
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$<${_cxx_cray}:-ffast-math>
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$<${_fortran_clang}:-ffast-math>
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$<${_cxx_clang}:-ffast-math>
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$<${_cxx_appleclang}:-ffast-math>
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$<${_cxx_crayclang}:-ffast-math>
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$<${_cxx_ibmclang}:-ffast-math>
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$<${_cxx_intelllvm}:-ffast-math>
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$<${_cxx_xlclang}:-ffast-math>
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$<${_cxx_msvc}:/fp:fast>
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)
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#
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# Floating point exceptions
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#

‎Tools/CMake/AMReXOptions.cmake‎

Lines changed: 1 addition & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -256,14 +256,8 @@ print_option(AMReX_GPU_RDC)
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#
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# Fast Math ================================================================
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#
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set(_FASTMATH_default OFF)
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if(AMReX_GPU_BACKEND STREQUAL CUDA) # note: historic settings
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# if(NOT AMReX_GPU_BACKEND STREQUAL NONE) # note: this would be more consistent for GPUs
262-
set(_FASTMATH_default ON)
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endif()
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option(AMReX_FASTMATH "Enable fast-math optimizations" ${_FASTMATH_default})
259+
option(AMReX_FASTMATH "Enable fast-math optimizations" OFF)
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print_option(AMReX_FASTMATH)
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unset(_FASTMATH_default)
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#
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# Parallel backends ========================================================

‎Tools/CMake/AMReXParallelBackends.cmake‎

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Original file line numberDiff line numberDiff line change
@@ -217,11 +217,6 @@ if (AMReX_SYCL)
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include(AMReXSYCL)
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foreach(D IN LISTS AMReX_SPACEDIM)
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target_link_libraries(amrex_${D}d PUBLIC SYCL)
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# fast math
222-
if(AMReX_FASTMATH)
223-
target_compile_options(amrex_${D}d PUBLIC -ffast-math)
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endif()
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endforeach()
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endif ()
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@@ -367,11 +362,6 @@ if (AMReX_HIP)
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foreach(D IN LISTS AMReX_SPACEDIM)
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target_compile_options(amrex_${D}d PUBLIC $<$<COMPILE_LANGUAGE:CXX>:-m64>)
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370-
# fast math
371-
if(AMReX_FASTMATH)
372-
target_compile_options(amrex_${D}d PUBLIC -ffast-math)
373-
endif()
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375365
# ROCm 4.5: use unsafe floating point atomics, otherwise atomicAdd is much slower
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#
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target_compile_options(amrex_${D}d PUBLIC $<$<COMPILE_LANGUAGE:CXX>:-munsafe-fp-atomics>)

‎Tools/CMake/AMReX_Config.cmake‎

Lines changed: 10 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -12,6 +12,13 @@
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#
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function (configure_amrex AMREX_TARGET)
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15+
#
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# Include the required modules
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#
18+
include( AMReX_ThirdPartyProfilers )
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include( AMReXGenexHelpers )
20+
include( AMReXFlagsTargets )
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#
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# Check if target "amrex" has been defined before
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# calling this macro
@@ -24,16 +31,11 @@ function (configure_amrex AMREX_TARGET)
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# Check that needed options have already been defined
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#
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if ( ( NOT ( DEFINED AMReX_MPI ) ) OR ( NOT (DEFINED AMReX_OMP) )
27-
OR ( NOT (DEFINED AMReX_PIC) ) OR (NOT (DEFINED AMReX_FPE)))
34+
OR ( NOT (DEFINED AMReX_PIC) ) OR (NOT (DEFINED AMReX_FASTMATH))
35+
OR (NOT (DEFINED AMReX_FPE)))
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message ( AUTHOR_WARNING "Required options are not defined" )
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endif ()
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31-
#
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# Include the required modules
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#
34-
include( AMReX_ThirdPartyProfilers )
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include( AMReXGenexHelpers )
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3739
#
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# Setup compilers
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#
@@ -147,19 +149,7 @@ function (configure_amrex AMREX_TARGET)
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148150
# fast math
149151
if (AMReX_FASTMATH)
150-
# GPU specific backends set in AMReXParallelBackends.cmake
151-
if (AMReX_GPU_BACKEND STREQUAL NONE)
152-
# See https://cmake.org/cmake/help/v4.1/variable/CMAKE_LANG_COMPILER_ID.html#variable:CMAKE_%3CLANG%3E_COMPILER_ID
153-
target_compile_options(${AMREX_TARGET} PUBLIC
154-
$<$<CXX_COMPILER_ID:AppleClang,Clang,CrayClang,GNU,IBMClang,IntelLLVM,XLClang>:-ffast-math>
155-
$<${_cxx_msvc}:"/fp:fast"> # MSVC
156-
)
157-
if (CMAKE_Fortran_COMPILER_LOADED)
158-
target_compile_options(${AMREX_TARGET} PUBLIC
159-
$<$<Fortran_COMPILER_ID:AppleClang,Clang,CrayClang,GNU,IBMClang,IntelLLVM,XLClang>:-ffast-math>
160-
)
161-
endif ()
162-
endif()
152+
target_link_libraries(${AMREX_TARGET} PUBLIC AMReX::Flags_FASTMATH)
163153
endif()
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#

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