[OpenMP] Fix gfortran bugzilla build bug 41755

[jlpeyton]

Summary

This patch provides workaround to allow gfortran to compile the OpenMP Fortran modules.

From the gfortran manual: https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gfortran/BOZ-literal-constants.html

"Note that initializing an INTEGER variable with a statement such as DATA i/Z'FFFFFFFF'/ will give an integer overflow error rather than the desired result of -1 when i is a 32-bit integer on a system that supports 64-bit integers. The `-fno-range-check' option can be used as a workaround for legacy code that initializes integers in this manner.

Bug filed: https://bugs.llvm.org/show_bug.cgi?id=41755

[Hahnfeld]

runtime/src/CMakeLists.txt

242–244

I think this should be CMAKE_Fortran_COMPILER_ID STREQUAL "GNU" if I finally understood variable expansion in its full glory from what we discussed in many other revisions. (Yeah, many places are still wrong, but we can start by not making it worse.)

Do we need a configure check that this flag is indeed available? Just thinking, but it seems that GCC has this flag since ages, even in 4.8.5. So maybe that's just unnecessary work.

In any case, please add a comment explaining that this is to workaround a bug in GCC (if I read the bug and @AndreyChurbanov's explanation correctly).

[jlpeyton]

Added comment and removed the variable expansion for CMAKE_Fortran_COMPILER_ID

I don't think we need to check for the flag since llvm requires gcc >= 5.1 and OpenMP runtime by itself requires 4.8.x.

[AndreyChurbanov]

LGTM

runtime/src/CMakeLists.txt

 endif()
 
 # Building the Fortran module files
 # One compilation step creates both omp_lib.mod and omp_lib_kinds.mod
 if(${LIBOMP_FORTRAN_MODULES})
   configure_file(${LIBOMP_INC_DIR}/omp_lib.h.var omp_lib.h @ONLY)
   configure_file(${LIBOMP_INC_DIR}/omp_lib.f.var omp_lib.f @ONLY)
   configure_file(${LIBOMP_INC_DIR}/omp_lib.f90.var omp_lib.f90 @ONLY)
+  if ("${CMAKE_Fortran_COMPILER_ID}" STREQUAL "GNU")
+    set(ADDITIONAL_Fortran_FLAGS "-fno-range-check")
+  endif()
   add_custom_target(libomp-mod ALL DEPENDS omp_lib.mod omp_lib_kinds.mod)
   libomp_get_fflags(LIBOMP_CONFIGURED_FFLAGS)
   if(CMAKE_Fortran_COMPILER_SUPPORTS_F90)
     set(LIBOMP_FORTRAN_SOURCE_FILE omp_lib.f90)
   else()
     set(LIBOMP_FORTRAN_SOURCE_FILE omp_lib.f)
   endif()
   add_custom_command(
     OUTPUT omp_lib.mod omp_lib_kinds.mod
-    COMMAND ${CMAKE_Fortran_COMPILER} -c ${LIBOMP_CONFIGURED_FFLAGS} ${LIBOMP_FORTRAN_SOURCE_FILE}
+    COMMAND ${CMAKE_Fortran_COMPILER} -c ${ADDITIONAL_Fortran_FLAGS}
+            ${LIBOMP_CONFIGURED_FFLAGS} ${LIBOMP_FORTRAN_SOURCE_FILE}
     DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${LIBOMP_FORTRAN_SOURCE_FILE}
       ${CMAKE_CURRENT_BINARY_DIR}/omp_lib.h
   )
   set_directory_properties(PROPERTIES ADDITIONAL_MAKE_CLEAN_FILES omp_lib${CMAKE_C_OUTPUT_EXTENSION})
 endif()
 
 # Move files to exports/ directory if requested
 if(${LIBOMP_COPY_EXPORTS})