if (CMAKE_Fortran_COMPILER_ID STREQUAL "GNU")
  set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -ffree-form -std=f2008ts -fimplicit-none -Werror=aliasing -Werror=ampersand -Werror=c-binding-type -Werror=intrinsic-shadow -Werror=intrinsics-std -Werror=line-truncation -Werror=tabs -Werror=target-lifetime -Werror=underflow -Werror=unused-but-set-parameter -Werror=unused-but-set-variable -Werror=unused-variable -Werror=unused-dummy-argument -Werror=conversion -Werror=zerotrip -Wno-maybe-uninitialized -Werror=unused-parameter")
  if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 10) # comparison against CXX version rather than GFortran version
    set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -fallow-argument-mismatch") # required for 10+ (MPI wrap)
   else ()
    set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -Werror=argument-mismatch")  # gcc 10+ has this automatically
  endif ()
  if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 13) # comparison against CXX version rather than GFortran version
    set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -Wno-error=uninitialized") # false positive (allocatable array)
  endif ()
  set(CMAKE_Fortran_FLAGS_RELEASE  "-O3 -g -funroll-loops")
  set(CMAKE_Fortran_FLAGS_COVERAGE "-O0 -g --coverage -fno-omit-frame-pointer -fcheck=all,no-array-temps -ffpe-trap=invalid,zero,overflow -fbacktrace -finit-real=snan -finit-integer=-42 -finit-derived -Werror=realloc-lhs -finline-matmul-limit=0 -Werror")
  set(CMAKE_Fortran_FLAGS_DEBUG    "-O2 -ggdb -fno-omit-frame-pointer -fcheck=all -ffpe-trap=invalid,zero,overflow -fbacktrace -finit-real=snan -finit-integer=-42 -finit-derived -finline-matmul-limit=0 -fsanitize=undefined -fsanitize=address -fsanitize-recover=all -Wall -Wextra -Werror -Werror=realloc-lhs -Wno-error=array-temporaries -Wno-error=compare-reals -Wno-error=function-elimination -Wno-error=surprising")
  if ((NOT (USE_MPI)) OR (NOT ("${MPI_Fortran_LIBRARY_VERSION_STRING}" MATCHES "Open MPI")))
    set(CMAKE_Fortran_FLAGS_DEBUG "${CMAKE_Fortran_FLAGS_DEBUG} -fsanitize=leak")
  endif ()
elseif (CMAKE_Fortran_COMPILER_ID STREQUAL "Intel")
  set(CMAKE_Fortran_FLAGS          "${CMAKE_Fortran_FLAGS} -free -stand=f18 -fpp -heap-arrays")
  set(CMAKE_Fortran_FLAGS_RELEASE  "-O3 -g")
  set(CMAKE_Fortran_FLAGS_DEBUG    "-O2 -debug")
elseif (CMAKE_Fortran_COMPILER_ID STREQUAL "PGI")
  set(CMAKE_Fortran_FLAGS          "${CMAKE_Fortran_FLAGS} -Mfreeform -Mextend -Mallocatable=03")  # -Mallocatable=03: enable F2003+ assignment semantics
  set(CMAKE_Fortran_FLAGS_RELEASE  "-fast")
  set(CMAKE_Fortran_FLAGS_DEBUG    "-g")
elseif (CMAKE_Fortran_COMPILER_ID STREQUAL "NAG")
  set(CMAKE_Fortran_FLAGS          "${CMAKE_Fortran_FLAGS} -f2008 -free -Warn=reallocation -Warn=subnormal")
  set(CMAKE_Fortran_FLAGS_RELEASE  "-O2")
  set(CMAKE_Fortran_FLAGS_DEBUG    "-g -C")
  if (NOT OpenMP_FOUND)
    set(CMAKE_Fortran_FLAGS_RELEASE  "${CMAKE_Fortran_FLAGS_RELEASE} -gline")  # -gline is only supported without OpenMP
    set(CMAKE_Fortran_FLAGS_DEBUG  "${CMAKE_Fortran_FLAGS_DEBUG} -C=all")  # some checks are not available with OpenMP
  endif ()
elseif (CMAKE_Fortran_COMPILER_ID STREQUAL "Cray")
  set(CMAKE_Fortran_FLAGS          "${CMAKE_Fortran_FLAGS} -f free -M3105 -ME7212")  # -M3105: hide a false-positive warning about modified loop variables due to loop fusing, promote warning 7212 to an error
  set(CMAKE_Fortran_FLAGS_RELEASE  "-O2 -G2")
  set(CMAKE_Fortran_FLAGS_DEBUG    "-G2")
  set(CMAKE_Fortran_MODOUT_FLAG    "-ef")  # override to get lower-case module file names
else ()
  message(WARNING "\
Unknown Fortran compiler, trying without any additional (optimization) flags.\n\
You will most likely have to specify extra options for free-form Fortran 2008 for your compiler!\n\
Please open an issue at https://github.com/cp2k/dbcsr/issues with the reported compiler name and the required flags.")
  message("-- CMAKE_Fortran_COMPILER_ID: " ${CMAKE_Fortran_COMPILER_ID})
  message("-- CMAKE_Fortran_COMPILER full path: " ${CMAKE_Fortran_COMPILER})
endif ()

if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
  set(CMAKE_CXX_FLAGS_RELEASE      "-O3 -g -funroll-loops -Wall -Wextra -Werror -Wno-missing-field-initializers")
  set(CMAKE_CXX_FLAGS_COVERAGE     "-O0 -g --coverage -Wall -Wextra -Werror -Wno-missing-field-initializers")
  set(CMAKE_CXX_FLAGS_DEBUG        "-O2 -ggdb -Wall -Wextra -Werror -Wno-missing-field-initializers -fsanitize=undefined -fsanitize=address -fsanitize-recover=all")
  if ((NOT (USE_MPI)) OR (NOT ("${MPI_Fortran_LIBRARY_VERSION_STRING}" MATCHES "Open MPI")))
    set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -fsanitize=leak")
  endif ()
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
  set(CMAKE_CXX_FLAGS_RELEASE      "-O3 -funroll-loops")
  set(CMAKE_CXX_FLAGS_COVERAGE     "-O0 -g --coverage")
  set(CMAKE_CXX_FLAGS_DEBUG        "-O0 -g")
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang")
  set(CMAKE_CXX_FLAGS_RELEASE      "-O3 -funroll-loops")
  set(CMAKE_CXX_FLAGS_COVERAGE     "-O0 -g --coverage")
  set(CMAKE_CXX_FLAGS_DEBUG        "-O0 -g")
  set(CMAKE_EXE_LINKER_FLAGS_COVERAGE "-lgcov")  # Apple's Clang needs an extra
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "Intel")
  set(CMAKE_CXX_FLAGS_RELEASE      "-O3 -g")
  set(CMAKE_CXX_FLAGS_DEBUG        "-O0 -debug")
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "PGI")
  set(CMAKE_CXX_FLAGS_RELEASE      "-fast")
  set(CMAKE_CXX_FLAGS_DEBUG        "-g")
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "Cray")
  set(CMAKE_CXX_FLAGS_RELEASE      "-O3")
  set(CMAKE_CXX_FLAGS_DEBUG        "-G2")
  if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9)
    # prevent deallocation failures due to tcmalloc's free with glibc's aligned_alloc, see https://bugzilla.redhat.com/show_bug.cgi?id=1569391
    set(CMAKE_C_FLAGS              "${CMAKE_C_FLAGS} -h system_alloc")
    set(CMAKE_CXX_FLAGS            "${CMAKE_CXX_FLAGS} -h system_alloc")
    set(CMAKE_Fortran_FLAGS        "${CMAKE_Fortran_FLAGS} -h system_alloc")
    # since the detection of the implicitly linked libraries occurs before we can intervene, filter them out again
    list(FILTER CMAKE_C_IMPLICIT_LINK_LIBRARIES EXCLUDE REGEX "tcmalloc")
    list(FILTER CMAKE_Fortran_IMPLICIT_LINK_LIBRARIES EXCLUDE REGEX "tcmalloc")
  endif ()
  # OpenACC support with CCE is EOL: causes https://github.com/cp2k/dbcsr/issues/261
  # eventually check compiler version (similar to -h system_alloc)
  set(CMAKE_C_FLAGS                "${CMAKE_C_FLAGS} -hnoacc -h nomessage=1234")
  set(CMAKE_CXX_FLAGS              "${CMAKE_CXX_FLAGS} -hnoacc -h nomessage=1234")
  set(CMAKE_Fortran_FLAGS          "${CMAKE_Fortran_FLAGS} -hnoacc -M1234")
else ()
  message(WARNING "\
Unknown C++ compiler, trying without any additional (optimization) flags.\n\
You may have to specify flags for C++11/14 support manually.\n\
Please open an issue at https://github.com/cp2k/dbcsr/issues with the reported compiler name and the required flags.")
  message("-- CMAKE_CXX_COMPILER_ID: " ${CMAKE_CXX_COMPILER_ID})
  message("-- CMAKE_CXX_COMPILER full path: " ${CMAKE_CXX_COMPILER})
endif ()

# inherit C flags from CXX
set(CMAKE_C_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
set(CMAKE_C_FLAGS_COVERAGE ${CMAKE_CXX_FLAGS_COVERAGE})
set(CMAKE_C_FLAGS_DEBUG ${CMAKE_CXX_FLAGS_DEBUG})