[flang] Handle Flang examples consistently with LLVM.

[vzakhari]

Summary

Without this change the problem is that flangOmpReport and
flangPrintFunctionNames libraries are not built under 'all',
but they are imported targets via LLVMExports.cmake so that
any out-of-tree build that configures upon LLVM+Flang package
will get this CMake error:

The imported target "flangPrintFunctionNames" references the file

    ".../lib/flangPrintFunctionNames.so"

but this file does not exist.

flang-aarch64-out-of-tree buildbot (https://lab.llvm.org/buildbot/#/builders/175)
does not catch this issue, because it does not enable Flang on the first stage.

The change is to adapt the LLVM macros from AddLLVM.cmake.
This is mostly a copy-paste, and it adds some maintenance burden
for Flang. Another option is to replace FLANG_BUILD_EXAMPLES
with LLVM_BUILD_EXAMPLES and just use the LLVM macros.

[PeteSteinfeld]

Thanks, Slava. You're a prince!

All builds and tests correctly and looks good.

[vzakhari]

In D145992#4190978, @PeteSteinfeld wrote:

Thanks, Slava. You're a prince!

All builds and tests correctly and looks good.

Thank you for the review, Pete :)

[awarzynski]

Thanks for these improvements, @vzakhari !

Another option is to replace FLANG_BUILD_EXAMPLES with LLVM_BUILD_EXAMPLES and just use the LLVM macros.

That would make sense to me. Also, why not re-use LLVM's add_llvm_example?

[vzakhari]

Got rid of FLANG_BUILD_EXAMPLES in favor of LLVM_BUILD_EXAMPLES.

[PeteSteinfeld]

Still looks good. Merge at will!

[awarzynski]

flang/CMakeLists.txt

433–434

[vzakhari]

flang/CMakeLists.txt

433–434

Good catch! Thanks!

flang/CMakeLists.txt

 
 option(FLANG_BUILD_TOOLS
   "Build the Flang tools. If OFF, just generate build targets." ON)
 if (FLANG_BUILD_TOOLS)
   add_subdirectory(tools)
 endif()
 add_subdirectory(runtime)
 
-option(FLANG_BUILD_EXAMPLES "Build Flang example programs by default." OFF)
-if (FLANG_BUILD_EXAMPLES AND FLANG_STANDALONE_BUILD)
-  message(FATAL_ERROR "Examples are not supported in out-of-tree builds.")
-endif()
+if (LLVM_INCLUDE_EXAMPLES)
   add_subdirectory(examples)
+endif()
 
 if (FLANG_INCLUDE_TESTS)
   add_subdirectory(test)
   if (FLANG_GTEST_AVAIL)
     add_subdirectory(unittests)
   endif ()
 endif()
 

flang/cmake/modules/AddFlang.cmake

macro(add_flang_tool name)
   endif()
 endmacro()
 
 macro(add_flang_symlink name dest)
   llvm_add_tool_symlink(FLANG ${name} ${dest} ALWAYS_GENERATE)
   # Always generate install targets
   llvm_install_symlink(FLANG ${name} ${dest} ALWAYS_GENERATE)
 endmacro()
-

flang/docs/FlangDriver.md

 `PluginAction`, through which it searches the plugin registry for the plugin
 name from `<name>`. If found, it returns the instantiated plugin, otherwise it
 reports an error diagnostic and returns `nullptr`.
 
 ## Enabling In-Tree Plugins
 For in-tree plugins, there is the CMake flag `FLANG_PLUGIN_SUPPORT`, enabled by
 default, that controls the exporting of executable symbols from `flang-new`,
 which plugins need access to. Additionally, there is the CMake flag
-`FLANG_BUILD_EXAMPLES`, turned off by default, that is used to control if the
+`LLVM_BUILD_EXAMPLES`, turned off by default, that is used to control if the
 example programs are built. This includes plugins that are in the
 `flang/example` directory and added as a `sub_directory` to the
 `flang/examples/CMakeLists.txt`, for example, the `PrintFlangFunctionNames`
 plugin. It is also possible to develop plugins out-of-tree.
 
 ## Limitations
 Note that the traversal API presented here is under active development and
 might change in the future. We expect it to evolve as support for new

flang/examples/CMakeLists.txt

-if(NOT FLANG_BUILD_EXAMPLES)
-  set_property(DIRECTORY PROPERTY EXCLUDE_FROM_ALL ON)
-endif()
-
 add_subdirectory(ExternalHelloWorld)
 add_subdirectory(PrintFlangFunctionNames)
 add_subdirectory(FlangOmpReport)

flang/examples/ExternalHelloWorld/CMakeLists.txt

-# This test is not run by default as it requires input.
-add_executable(external-hello-world
-  external-hello.cpp
+set(LLVM_LINK_COMPONENTS
+  FortranRuntime
   )
 
-target_link_libraries(external-hello-world
-  FortranRuntime
+# This test is not run by default as it requires input.
+add_llvm_example(external-hello-world
+  external-hello.cpp
 )

flang/examples/FlangOmpReport/CMakeLists.txt

-add_llvm_library(flangOmpReport
+add_llvm_example_library(flangOmpReport
   MODULE
   FlangOmpReport.cpp
   FlangOmpReportVisitor.cpp
 
   DEPENDS
   acc_gen
   flangFrontend
   omp_gen
 )

flang/examples/PrintFlangFunctionNames/CMakeLists.txt

 # TODO: Note that this is currently only available on Linux.
 # On Windows, we would also have to specify e.g. `PLUGIN_TOOL`.
-add_llvm_library(flangPrintFunctionNames
+add_llvm_example_library(flangPrintFunctionNames
     MODULE
     PrintFlangFunctionNames.cpp
 
     DEPENDS
     acc_gen
     flangFrontend
     omp_gen
 )

flang/test/CMakeLists.txt

 # Test runner infrastructure for Flang. This configures the Flang test trees
 # for use by Lit, and delegates to LLVM's lit test handlers.
 add_subdirectory(lib)
 
 llvm_canonicalize_cmake_booleans(
-  FLANG_BUILD_EXAMPLES
   FLANG_STANDALONE_BUILD
+  LLVM_BUILD_EXAMPLES
   LLVM_BYE_LINK_INTO_TOOLS
   LLVM_ENABLE_PLUGINS
 )
 
 set(FLANG_TOOLS_DIR ${FLANG_BINARY_DIR}/bin)
 
 # FIXME In out-of-tree builds, "SHLIBDIR" is undefined and passing it to
 # `configure_lit_site_cfg` leads to a configuration error. This is currently

 endif()
 
 if (FLANG_INCLUDE_TESTS)
   if (FLANG_GTEST_AVAIL)
     list(APPEND FLANG_TEST_DEPENDS FlangUnitTests)
   endif()
 endif()
 
-if (FLANG_BUILD_EXAMPLES)
+if (LLVM_BUILD_EXAMPLES)
   list(APPEND FLANG_TEST_DEPENDS
     flangPrintFunctionNames
     flangOmpReport
     )
 endif ()
 
 add_custom_target(flang-test-depends DEPENDS ${FLANG_TEST_DEPENDS})
 

flang/test/Examples/print-fns-calls.f90

 ! Check the Flang Print Function Names example plugin doesn't count/print function/subroutine calls (should only count definitions)
-! This requires that the examples are built (FLANG_BUILD_EXAMPLES=ON) to access flangPrintFunctionNames.so
+! This requires that the examples are built (LLVM_BUILD_EXAMPLES=ON) to access flangPrintFunctionNames.so
 
 ! REQUIRES: plugins, examples, shell
 
 ! RUN: %flang_fc1 -load %llvmshlibdir/flangPrintFunctionNames%pluginext -plugin print-fns %s 2>&1 | FileCheck %s
 
 ! CHECK: ==== Functions: 0 ====
 ! CHECK-NEXT: ==== Subroutines: 0 ====
 
 program main
     call subroutine1
     fn1 = function1()
     fn2 = function2()
 end program main

flang/test/Examples/print-fns-definitions.f90

 ! Check the Flang Print Function Names example plugin prints and counts function/subroutine definitions
 ! This includes internal and external Function/Subroutines, but not Statement Functions
-! This requires that the examples are built (FLANG_BUILD_EXAMPLES=ON) to access flangPrintFunctionNames.so
+! This requires that the examples are built (LLVM_BUILD_EXAMPLES=ON) to access flangPrintFunctionNames.so
 
 ! REQUIRES: plugins, examples, shell
 
 ! RUN: %flang_fc1 -load %llvmshlibdir/flangPrintFunctionNames%pluginext -plugin print-fns %s 2>&1 | FileCheck %s
 
 ! CHECK: Function: external_func1
 ! CHECK-NEXT: Function: external_func2
 ! CHECK-NEXT: Subroutine: external_subr

flang/test/Examples/print-fns-interfaces.f90

 ! Check the Flang Print Function Names example plugin doesn't count/print Functions/Subroutines in interfaces
 ! (It should only count definitions, which will appear elsewhere for interfaced functions/subroutines)
-! This requires that the examples are built (FLANG_BUILD_EXAMPLES=ON) to access flangPrintFunctionNames.so
+! This requires that the examples are built (LLVM_BUILD_EXAMPLES=ON) to access flangPrintFunctionNames.so
 
 ! REQUIRES: plugins, examples, shell
 
 ! RUN: %flang_fc1 -load %llvmshlibdir/flangPrintFunctionNames%pluginext -plugin print-fns %s 2>&1 | FileCheck %s
 
 ! CHECK: ==== Functions: 0 ====
 ! CHECK-NEXT: ==== Subroutines: 0 ====
 

flang/test/lit.site.cfg.py.in

 config.errc_messages = "@LLVM_LIT_ERRC_MESSAGES@"
 config.flang_obj_root = "@FLANG_BINARY_DIR@"
 config.flang_src_dir = "@FLANG_SOURCE_DIR@"
 config.flang_tools_dir = lit_config.substitute("@FLANG_TOOLS_DIR@")
 config.flang_intrinsic_modules_dir = "@FLANG_INTRINSIC_MODULES_DIR@"
 config.flang_llvm_tools_dir = "@CMAKE_BINARY_DIR@/bin"
 config.flang_lib_dir = "@CMAKE_BINARY_DIR@/lib"
 config.flang_test_triple = "@FLANG_TEST_TARGET_TRIPLE@"
-config.flang_examples = @FLANG_BUILD_EXAMPLES@
+config.flang_examples = @LLVM_BUILD_EXAMPLES@
 config.python_executable = "@PYTHON_EXECUTABLE@"
 config.flang_standalone_build = @FLANG_STANDALONE_BUILD@
 config.has_plugins = @LLVM_ENABLE_PLUGINS@
 config.linked_bye_extension = @LLVM_BYE_LINK_INTO_TOOLS@
 config.cc = "@CMAKE_C_COMPILER@"
 config.targets_to_build = "@TARGETS_TO_BUILD@"
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@FLANG_SOURCE_DIR@/test/lit.cfg.py")