[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

438

[vzakhari]

flang/CMakeLists.txt

438

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)
+set(FLANG_EXAMPLES_INSTALL_DIR "examples" CACHE STRING
+    "Path for examples subdirectory (enabled by FLANG_BUILD_EXAMPLES=ON) (defaults to 'examples')")
+mark_as_advanced(FLANG_EXAMPLES_INSTALL_DIR)
 if (FLANG_BUILD_EXAMPLES AND FLANG_STANDALONE_BUILD)
   message(FATAL_ERROR "Examples are not supported in out-of-tree builds.")
 endif()
 add_subdirectory(examples)
 
 if (FLANG_INCLUDE_TESTS)
   add_subdirectory(test)
   if (FLANG_GTEST_AVAIL)
     add_subdirectory(unittests)
   endif ()

flang/cmake/modules/AddFlang.cmake

 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()
 
+macro(add_flang_example name)
+  if (NOT FLANG_BUILD_EXAMPLES)
+    set(EXCLUDE_FROM_ALL ON)
+  endif()
+  add_llvm_executable(${name} ${ARGN})
+  if (FLANG_BUILD_EXAMPLES)
+    install(TARGETS ${name} RUNTIME DESTINATION "${FLANG_EXAMPLES_INSTALL_DIR}")
+  endif()
+  set_target_properties(${name} PROPERTIES FOLDER "Examples")
+endmacro(add_flang_example name)
+
+macro(add_flang_example_library name)
+  if (NOT FLANG_BUILD_EXAMPLES)
+    set(EXCLUDE_FROM_ALL ON)
+    add_llvm_library(${name} BUILDTREE_ONLY ${ARGN})
+  else()
+    add_llvm_library(${name} ${ARGN})
+  endif()
+
+  set_target_properties(${name} PROPERTIES FOLDER "Examples")
+endmacro(add_flang_example_library name)

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_flang_example(external-hello-world
+  external-hello.cpp
 )

flang/examples/FlangOmpReport/CMakeLists.txt

-add_llvm_library(flangOmpReport
+add_flang_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_flang_example_library(flangPrintFunctionNames
     MODULE
     PrintFlangFunctionNames.cpp
 
     DEPENDS
     acc_gen
     flangFrontend
     omp_gen
 )