if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
  # Rely on llvm-config.
  set(CONFIG_OUTPUT)
  find_program(LLVM_CONFIG "llvm-config")
  if(DEFINED LLVM_PATH)
    set(LLVM_INCLUDE_DIR ${LLVM_INCLUDE_DIR} CACHE PATH "Path to llvm/include")
    set(LLVM_PATH ${LLVM_PATH} CACHE PATH "Path to LLVM source tree")
    set(LLVM_MAIN_SRC_DIR ${LLVM_PATH})
    set(LLVM_CMAKE_PATH "${LLVM_PATH}/cmake/modules")
  elseif(LLVM_CONFIG)
    message(STATUS "Found LLVM_CONFIG as ${LLVM_CONFIG}")
    set(CONFIG_COMMAND ${LLVM_CONFIG}
      "--includedir"
      "--prefix"
      "--src-root")
    execute_process(
      COMMAND ${CONFIG_COMMAND}
      RESULT_VARIABLE HAD_ERROR
      OUTPUT_VARIABLE CONFIG_OUTPUT
    )
    if(NOT HAD_ERROR)
      string(REGEX REPLACE
        "[ \t]*[\r\n]+[ \t]*" ";"
        CONFIG_OUTPUT ${CONFIG_OUTPUT})
    else()
      string(REPLACE ";" " " CONFIG_COMMAND_STR "${CONFIG_COMMAND}")
      message(STATUS "${CONFIG_COMMAND_STR}")
      message(FATAL_ERROR "llvm-config failed with status ${HAD_ERROR}")
    endif()

    list(GET CONFIG_OUTPUT 0 INCLUDE_DIR)
    list(GET CONFIG_OUTPUT 1 LLVM_OBJ_ROOT)
    list(GET CONFIG_OUTPUT 2 MAIN_SRC_DIR)

    set(LLVM_INCLUDE_DIR ${INCLUDE_DIR} CACHE PATH "Path to llvm/include")
    set(LLVM_BINARY_DIR ${LLVM_OBJ_ROOT} CACHE PATH "Path to LLVM build tree")
    set(LLVM_MAIN_SRC_DIR ${MAIN_SRC_DIR} CACHE PATH "Path to LLVM source tree")
    set(LLVM_CMAKE_PATH "${LLVM_BINARY_DIR}/share/llvm/cmake")
  else()
    message(FATAL_ERROR "llvm-config not found and LLVM_MAIN_SRC_DIR not defined. "
                        "Reconfigure with -DLLVM_CONFIG=path/to/llvm-config "
                        "or -DLLVM_PATH=path/to/llvm-source-root.")
  endif()

  if (NOT EXISTS ${LLVM_MAIN_SRC_DIR})
    message(FATAL_ERROR "Not found: ${LLVM_MAIN_SRC_DIR}")
  endif()

  if(NOT EXISTS ${LLVM_CMAKE_PATH})
    message(FATAL_ERROR "Not found: ${LLVM_CMAKE_PATH}")
  endif()

  list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
  list(APPEND CMAKE_MODULE_PATH "${LLVM_MAIN_SRC_DIR}/cmake/modules")


  if(LLVM_LIT)
    # Define the default arguments to use with 'lit', and an option for the user
    # to override.
    set(LIT_ARGS_DEFAULT "-sv --show-xfail --show-unsupported")
    if (MSVC OR XCODE)
      set(LIT_ARGS_DEFAULT "${LIT_ARGS_DEFAULT} --no-progress-bar")
    endif()
    set(LLVM_LIT_ARGS "${LIT_ARGS_DEFAULT}" CACHE STRING "Default options for lit")

    # On Win32 hosts, provide an option to specify the path to the GnuWin32 tools.
    if( WIN32 AND NOT CYGWIN )
      set(LLVM_LIT_TOOLS_DIR "" CACHE PATH "Path to GnuWin32 tools")
    endif()
  else()
    set(LLVM_INCLUDE_TESTS OFF)
  endif()

  include(AddLLVM) # Include the LLVM CMake functions.
  include(HandleLLVMOptions)
  set(LIBCXX_BUILT_STANDALONE 1)
else()
  set(LLVM_MAIN_SRC_DIR "${CMAKE_SOURCE_DIR}" CACHE PATH "Path to LLVM source tree")
  set(LLVM_LIT "${CMAKE_SOURCE_DIR}/utils/lit/lit.py")
endif()