# CheckIPOSupported

New in version 3.9.

Check whether the compiler supports an interprocedural optimization (IPO/LTO). Use this before enabling the `INTERPROCEDURAL_OPTIMIZATION` target property.

`check_ipo_supported`

      check_ipo_supported([RESULT <result>] [OUTPUT <output>]
                          [LANGUAGES <lang>...])

  Options are:

  `RESULT <result>`

    Set `<result>` variable to `YES` if IPO is supported by the compiler and `NO` otherwise. If this option is not given then the command will issue a fatal error if IPO is not supported.

  `OUTPUT <output>`

    Set `<output>` variable with details about any error.

  `LANGUAGES <lang>...`

    Specify languages whose compilers to check. Languages `C`, `CXX`, and `Fortran` are supported.

It makes no sense to use this module when `CMP0069` is set to `OLD` so module will return error in this case. See policy `CMP0069` for details.

## Examples

    check_ipo_supported() # fatal error if IPO is not supported
    set_property(TARGET foo PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)

    # Optional IPO. Do not use IPO if it's not supported by compiler.
    check_ipo_supported(RESULT result OUTPUT output)
    if(result)
      set_property(TARGET foo PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
    else()
      message(WARNING "IPO is not supported: ${output}")
    endif()