[Flang] Remove FLANG_INCLUDE_RUNTIME (#124126)

Remove the FLANG_INCLUDE_RUNTIME option which was replaced by
LLVM_ENABLE_RUNTIMES=flang-rt.

The FLANG_INCLUDE_RUNTIME option was added in #122336 which disables the
non-runtimes build instructions for the Flang runtime so they do not
conflict with the LLVM_ENABLE_RUNTIMES=flang-rt option added in #110217.
In order to not maintain multiple build instructions for the same thing,
this PR completely removes the old build instructions (effectively
forcing FLANG_INCLUDE_RUNTIME=OFF).

As per discussion in
https://discourse.llvm.org/t/buildbot-changes-with-llvm-enable-runtimes-flang-rt/83571/2
we now implicitly add LLVM_ENABLE_RUNTIMES=flang-rt whenever Flang is
compiled in a bootstrapping (non-standalone) build. Because it is
possible to build Flang-RT separately, this behavior can be disabled
using `-DFLANG_ENABLE_FLANG_RT=OFF`. Also see the discussion an
implicitly adding runtimes/projects in #123964.

Author: Meinersbur

flang-rt/README.md

@@ -91,7 +91,12 @@ can be any compiler supporting the same ABI.
 In addition to the compiler, the build must be able to find LLVM development
 tools such as `lit` and `FileCheck` that are not found in an LLVM's install
 directory. Use `CMAKE_BINARY_DIR` to point to directory where LLVM has
-been built. A simple build configuration might look like the following:
+been built. When building Flang as part of a bootstrapping build
+(`LLVM_ENABLE_PROJECTS=flang`), Flang-RT is automatically added
+unless configured with `-DFLANG_ENABLE_FLANG_RT=OFF`. Add that option to avoid
+having two conflicting versions of the same library.
+
+A simple build configuration might look like the following:
 
 ```bash
 cmake -S <path-to-llvm-project-source>/runtimes              \

flang/CMakeLists.txt

@@ -23,7 +23,6 @@ if (LLVM_ENABLE_EH)
 endif()
 
 set(FLANG_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
-set(FLANG_RT_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../flang-rt")
 
 # Python is needed for symbol extracting tool
 set(LLVM_MINIMUM_PYTHON_VERSION 3.8)
@@ -259,24 +258,10 @@ else()
   include_directories(SYSTEM ${MLIR_TABLEGEN_OUTPUT_DIR})
 endif()
 
-set(FLANG_INCLUDE_RUNTIME_default ON)
-if ("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
-  set(FLANG_INCLUDE_RUNTIME_default OFF)
-endif ()
-option(FLANG_INCLUDE_RUNTIME "Build the runtime in-tree (deprecated; to be replaced with LLVM_ENABLE_RUNTIMES=flang-rt)" ${FLANG_INCLUDE_RUNTIME_default})
-if (FLANG_INCLUDE_RUNTIME)
-  if ("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
-    message(WARNING "Building Flang-RT using LLVM_ENABLE_RUNTIMES. FLANG_INCLUDE_RUNTIME=${FLANG_INCLUDE_RUNTIME} ignored.")
-    set(FLANG_INCLUDE_RUNTIME OFF)
-  else ()
-     message(STATUS "Building Flang-RT in-tree")
-  endif ()
-else ()
-  if ("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
-    message(STATUS "Building Flang-RT using LLVM_ENABLE_RUNTIMES")
-  else ()
-    message(STATUS "Not building Flang-RT. For a usable Fortran toolchain, either add LLVM_ENABLE_RUNTIMES=flang-rt, or compile a standalone Flang-RT.")
-  endif ()
+if (FLANG_STANDALONE_BUILD)
+  message(STATUS "Not building Flang-RT. For a usable Fortran toolchain, compile a standalone Flang-RT.")
+elseif (NOT "flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
+  message(STATUS "Not building Flang-RT. For a usable Fortran toolchain, either set FLANG_ENABLE_FLANG_RT=ON, add LLVM_ENABLE_RUNTIMES=flang-rt, or compile a standalone Flang-RT.")
 endif ()
 
 set(FLANG_TOOLS_INSTALL_DIR "${CMAKE_INSTALL_BINDIR}" CACHE PATH
@@ -501,12 +486,6 @@ if (FLANG_INCLUDE_TESTS)
   add_compile_definitions(FLANG_INCLUDE_TESTS=1)
 endif()
 
-option(FLANG_CUF_RUNTIME
-  "Compile CUDA Fortran runtime sources" OFF)
-if (FLANG_CUF_RUNTIME)
-  find_package(CUDAToolkit REQUIRED)
-endif()
-
 add_subdirectory(include)
 add_subdirectory(lib)
 add_subdirectory(cmake/modules)
@@ -517,10 +496,6 @@ if (FLANG_BUILD_TOOLS)
   add_subdirectory(tools)
 endif()
 
-if (FLANG_INCLUDE_RUNTIME)
-  add_subdirectory(runtime)
-endif ()
-
 if (LLVM_INCLUDE_EXAMPLES)
   add_subdirectory(examples)
 endif()

flang/cmake/modules/AddFlangOffloadRuntime.cmake

@@ -1,6 +1,3 @@
-if (FLANG_INCLUDE_RUNTIME)
-  add_subdirectory(ExternalHelloWorld)
-endif ()
 add_subdirectory(PrintFlangFunctionNames)
 add_subdirectory(FlangOmpReport)
 add_subdirectory(FeatureList)