# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
# file Copyright.txt or https://cmake.org/licensing for details.

#[=======================================================================[.rst:
CheckIPOSupported
-----------------

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

.. command:: 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`` and ``CXX`` are supported.

Examples
^^^^^^^^

.. code-block:: cmake

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

.. code-block:: cmake

  # 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()

#]=======================================================================]

include(CMakeParseArguments) # cmake_parse_arguments

# X_RESULT - name of the final result variable
# X_OUTPUT - name of the variable with information about error
macro(_ipo_not_supported output)
  string(COMPARE EQUAL "${X_RESULT}" "" is_empty)
  if(is_empty)
    message(FATAL_ERROR "IPO is not supported (${output}).")
  endif()

  set("${X_RESULT}" NO PARENT_SCOPE)
  set("${X_OUTPUT}" "${output}" PARENT_SCOPE)
endmacro()

# Run IPO/LTO test
macro(_ipo_run_language_check language)
  set(testdir "${CMAKE_CURRENT_BINARY_DIR}/_CMakeLTOTest-${language}")

  file(REMOVE_RECURSE "${testdir}")
  file(MAKE_DIRECTORY "${testdir}")

  set(bindir "${testdir}/bin")
  set(srcdir "${testdir}/src")

  file(MAKE_DIRECTORY "${bindir}")
  file(MAKE_DIRECTORY "${srcdir}")

  set(TRY_COMPILE_PROJECT_NAME "lto-test")

  set(try_compile_src "${CMAKE_ROOT}/Modules/CheckIPOSupported")

  # Use:
  # * TRY_COMPILE_PROJECT_NAME
  # * CMAKE_VERSION
  configure_file(
      "${try_compile_src}/CMakeLists-${language}.txt.in"
      "${srcdir}/CMakeLists.txt"
      @ONLY
  )

  string(COMPARE EQUAL "${language}" "C" is_c)
  string(COMPARE EQUAL "${language}" "CXX" is_cxx)

  if(is_c)
    set(copy_sources foo.c main.c)
  elseif(is_cxx)
    set(copy_sources foo.cpp main.cpp)
  else()
    message(FATAL_ERROR "Language not supported")
  endif()

  foreach(x ${copy_sources})
    configure_file(
        "${try_compile_src}/${x}"
        "${srcdir}/${x}"
        COPYONLY
    )
  endforeach()

  try_compile(
      result
      "${bindir}"
      "${srcdir}"
      "${TRY_COMPILE_PROJECT_NAME}"
      CMAKE_FLAGS
      "-DCMAKE_VERBOSE_MAKEFILE=ON"
      "-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON"
      OUTPUT_VARIABLE output
  )

  if(NOT result)
    _ipo_not_supported("${output}")
    return()
  endif()
endmacro()

function(check_ipo_supported)
  # TODO: IPO policy

  set(optional)
  set(one RESULT OUTPUT)
  set(multiple LANGUAGES)

  # Introduce:
  # * X_RESULT
  # * X_OUTPUT
  # * X_LANGUAGES
  cmake_parse_arguments(X "${optional}" "${one}" "${multiple}" "${ARGV}")

  string(COMPARE NOTEQUAL "${X_UNPARSED_ARGUMENTS}" "" has_unparsed)
  if(has_unparsed)
    message(FATAL_ERROR "Unparsed arguments: ${X_UNPARSED_ARGUMENTS}")
  endif()

  string(COMPARE EQUAL "${X_LANGUAGES}" "" no_languages)
  if(no_languages)
    # User did not set any languages, use defaults
    get_property(enabled_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
    string(COMPARE EQUAL "${enabled_languages}" "" no_languages)
    if(no_languages)
      _ipo_not_supported(
          "no languages found in ENABLED_LANGUAGES global property"
      )
      return()
    endif()

    set(languages "")
    list(FIND enabled_languages "CXX" result)
    if(NOT result EQUAL -1)
      list(APPEND languages "CXX")
    endif()

    list(FIND enabled_languages "C" result)
    if(NOT result EQUAL -1)
      list(APPEND languages "C")
    endif()

    list(FIND enabled_languages "Fortran" result)
    if(NOT result EQUAL -1)
      list(APPEND languages "Fortran")
    endif()

    string(COMPARE EQUAL "${languages}" "" no_languages)
    if(no_languages)
      _ipo_not_supported(
          "no C/CXX/Fortran languages found in ENABLED_LANGUAGES global property"
      )
      return()
    endif()
  else()
    set(languages "${X_LANGUAGES}")

    set(unsupported_languages "${languages}")
    list(REMOVE_ITEM unsupported_languages "C" "CXX" "Fortran")
    string(COMPARE NOTEQUAL "${unsupported_languages}" "" has_unsupported)
    if(has_unsupported)
      _ipo_not_supported(
          "language(s) '${unsupported_languages}' not supported"
      )
      return()
    endif()
  endif()

  list(FIND languages "Fortran" result)
  if(NOT result EQUAL -1)
    _ipo_not_supported("Fortran is not supported")
    return()
  endif()

  if(NOT _CMAKE_IPO_SUPPORTED_BY_CMAKE)
    _ipo_not_supported("CMake doesn't support IPO for current compiler")
    return()
  endif()

  if(NOT _CMAKE_IPO_MAY_BE_SUPPORTED_BY_COMPILER)
    _ipo_not_supported("compiler doesn't support IPO")
    return()
  endif()

  foreach(x ${languages})
    _ipo_run_language_check(${x})
  endforeach()

  set("${X_RESULT}" YES PARENT_SCOPE)
endfunction()