Portable Compiler Flags

To simplify the development of code that is portable across different architectures and compilers, BLT provides the blt_append_custom_compiler_flag macro, which allows users to easily place a compiler dependent flag into a CMake variable.


To use this macro, supply a cmake variable in which to append a flag (FLAGS_VAR), and the appropriate flag for each of our supported compilers.

This macro currently supports the following compilers:

  • GNU


  • XL (IBM compiler)

  • INTEL (Intel compiler)

  • MSVC (Microsoft Visual Studio)

  • MSVC_INTEL (Intel toolchain in Microsoft Visual Studio)

  • PGI

Here is an example for setting the appropriate flag to treat warnings as errors:

  DEFAULT  "-Werror"
  MSVC     "/WX"
  XL       "qhalt=w"

Since values for GNU, CLANG and INTEL are not supplied, they will get the default value, -Werror, which is supplied by the macro’s DEFAULT argument.

BLT also provides a simple macro to add compiler flags to a target. You can append the above compiler flag to an already defined executable, such as example_1 with the following line:

blt_add_target_compile_flags(TO example_1
                             FLAGS BLT_WARNINGS_AS_ERRORS_FLAG )

Here is another example to disable warnings about unknown OpenMP pragmas in the code:

# Flag for disabling warnings about omp pragmas in the code
    DEFAULT "-Wno-unknown-pragmas"
    XL      "-qignprag=omp"
    INTEL   "-diag-disable 3180"
    MSVC    "/wd4068"


GNU does not have a way to only disable warnings about OpenMP pragmas, so you must disable warnings about all unknown pragmas on this compiler.