Design and expression of compilation and run time options

[suvarchal]

Consider the following points:

• CMakeLists.txt in the root directory has a few options :

  fesom2/CMakeLists.txt

  Lines 13 to 19 in 21470c4

  	option(BUILD_SHARED_LIBS "Build using shared libraries" OFF) # cmake-internal switch to toggle if library targets are being build as STATIC or SHARED, see https://cmake.org/cmake/help/latest/guide/tutorial/Selecting%20Static%20or%20Shared%20Libraries.html
  	set(TOPLEVEL_DIR ${CMAKE_CURRENT_LIST_DIR})
  	set(FESOM_COUPLED OFF CACHE BOOL "compile fesom standalone or with oasis support (i.e. coupled)")
  	set(OIFS_COUPLED OFF CACHE BOOL "compile fesom coupled to OpenIFS. (Also needs FESOM_COUPLED to work)")
  	set(CRAY OFF CACHE BOOL "compile with cray ftn")
  	set(USE_ICEPACK OFF CACHE BOOL "compile fesom with the Iceapck modules for sea ice column physics.")
  	set(OPENMP_REPRODUCIBLE OFF CACHE BOOL "serialize OpenMP loops that are critical for reproducible results")

  
  that seems could be a nice way to consolidate all fesom specific build options into one file but then there are fesom specific options like ENABLE_OPENMP, others defined in src/CMakeLists.txt. This, apart from making main CMakeLists.txt somewhat irrelevant and makes one not to trust the options in it and one always has to check whats set in src/CMakeLists.txt.
• I am finding it hard to take scattered machine specific options in src/CMakeLists.txt, for instance machine specific options exist based on FESOM_PLATFORM_STRATEGY for levante, albedo, aleph etc and are further split using ifs based on what compiler is used . It is not like if based on $FESOM_PLATFORM_STRATEGY is in one block if it can be at-times scattered at different locations. e.g,

  fesom2/src/CMakeLists.txt

  Lines 38 to 40 in 21470c4

  	if(${FESOM_PLATFORM_STRATEGY} STREQUAL levante.dkrz.de )
  	message(STATUS "multithreading disabled for Levante") # multithreading suddenly produces an error, disable it until a fix is found. issue #413
  	option(DISABLE_MULTITHREADING "disable asynchronous operations" ON)

  and compiler ifs

  fesom2/src/CMakeLists.txt

  Lines 147 to 154 in 21470c4

  	if(${CMAKE_Fortran_COMPILER_ID} STREQUAL Intel )
  	if(${BUILD_FESOM_AS_LIBRARY})
  	target_compile_options(${PROJECT_NAME} PRIVATE -r8 -i4 -fp-model precise -no-prec-div -no-prec-sqrt -fimf-use-svml -xHost -ip -init=zero -no-wrap-margin -fpe0) # add -fpe0 for RAPS environment
  	else()
  	target_compile_options(${PROJECT_NAME} PRIVATE -r8 -i4 -fp-model precise -no-prec-div -no-prec-sqrt -fimf-use-svml -ip -init=zero -no-wrap-margin)
  	endif()
  	if(${FESOM_PLATFORM_STRATEGY} STREQUAL levante.dkrz.de )
  	target_compile_options(${PROJECT_NAME} PRIVATE -march=core-avx2 -mtune=core-avx2)

• env/machine/shell.xx seems to me a somewhat modular/elegant way to add a new machine with different compilers, this is currently just part of the story for building and running on that machine: one may need to add machine and compiler specific options in src/CMakelists.txt and at run time also change paths for input data for a machine in namelist.forcing,config even though we know we are on a specific machine paths are likely to be same, and find template job script from a different directory work. I wonder can this all be simplified by putting all relevant files for a particular machine in env. This also i think can reduce maintaining src/CMakeLists.txt (for example a machine reached EOL) and delegate burden of maintenance of machine specific options to users of the machine.

I think this needs to be thought of otherwise we make a mini RAPS, that may become a burden on developers and new comers.

This is to open a discussion on the issue and solutions.