[runtimes] Add the ability to include out of tree runtimes

[ldionne]

Summary

LLVM_EXTERNAL_RUNTIMES is similar to LLVM_EXTERNAL_PROJECTS: the
source directory for the external runtime is resolved through the
LLVM_EXTERNAL_<proj>_SOURCE_DIR variable.

This makes it easier to experiment with additional runtimes locally
and provides a relatively low maintenance hook for downstreams to
add their own runtimes outside of the LLVM tree.

[Mordante]

llvm/docs/CMake.rst

634

IMO There should be a way to pass additional arguments to CMake for the external libraries, including documentation how to do that.

llvm/docs/CMake.rst

 **LLVM_EXTERNAL_PROJECTS**:STRING
   Semicolon-separated list of additional external projects to build as part of
   llvm. For each project LLVM_EXTERNAL_<NAME>_SOURCE_DIR have to be specified
   with the path for the source code of the project. Example:
   ``-DLLVM_EXTERNAL_PROJECTS="Foo;Bar"
   -DLLVM_EXTERNAL_FOO_SOURCE_DIR=/src/foo
   -DLLVM_EXTERNAL_BAR_SOURCE_DIR=/src/bar``.
 
+**LLVM_EXTERNAL_RUNTIMES**:STRING
+  Semicolon-separated list of additional external runtimes to build. For each
+  additional runtime LLVM_EXTERNAL_<NAME>_SOURCE_DIR has to be specified with
+  the path for the source code of the project. Example:
+  ``-DLLVM_EXTERNAL_RUNTIMES="mylib1;mylib2"
+  -DLLVM_EXTERNAL_MYLIB1_SOURCE_DIR=/src/mylib1
+  -DLLVM_EXTERNAL_MYLIB2_SOURCE_DIR=/src/mylib2``.
+
 **LLVM_EXTERNALIZE_DEBUGINFO**:BOOL
   Generate dSYM files and strip executables and libraries (Darwin Only).
   Defaults to OFF.
 
 **LLVM_FORCE_USE_OLD_TOOLCHAIN**:BOOL
   If enabled, the compiler and standard library versions won't be checked. LLVM
   may not compile at all, or might fail at runtime due to known bugs in these
   toolchains.

llvm/runtimes/CMakeLists.txt

if(IS_DIRECTORY ${proj_dir} AND EXISTS ${proj_dir}/CMakeLists.txt)
     list(APPEND runtimes ${proj_dir})
   else()
     message(FATAL_ERROR "LLVM_ENABLE_RUNTIMES requests ${proj} but directory not found: ${proj_dir}")
   endif()
   string(TOUPPER "${proj}" canon_name)
   STRING(REGEX REPLACE "-" "_" canon_name ${canon_name})
   set(LLVM_EXTERNAL_${canon_name}_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../../${proj}")
 endforeach()
+if(LLVM_EXTERNAL_RUNTIMES)
+  string(REPLACE ";" "|" LLVM_EXTERNAL_RUNTIMES_PASSTHROUGH "${LLVM_EXTERNAL_RUNTIMES}")
+  list(APPEND EXTERNAL_RUNTIMES_CMAKE_ARGS -DLLVM_EXTERNAL_RUNTIMES=${LLVM_EXTERNAL_RUNTIMES_PASSTHROUGH})
+endif()
+foreach(proj ${LLVM_EXTERNAL_RUNTIMES})
+  string(TOUPPER "${proj}" canon_name)
+  STRING(REGEX REPLACE "-" "_" canon_name ${canon_name})
+  set(LLVM_EXTERNAL_${canon_name}_SOURCE_DIR
+    "${LLVM_EXTERNAL_${canon_name}_SOURCE_DIR}"
+    CACHE PATH "Path to ${proj} source directory")
+  list(APPEND EXTERNAL_RUNTIMES_CMAKE_ARGS
+    "-DLLVM_EXTERNAL_${canon_name}_SOURCE_DIR=${LLVM_EXTERNAL_${canon_name}_SOURCE_DIR}")
+endforeach()
 
 function(get_compiler_rt_path path)
   foreach(entry ${runtimes})
     get_filename_component(projName ${entry} NAME)
     if("${projName}" MATCHES "compiler-rt")
       set(${path} ${entry} PARENT_SCOPE)
       return()
     endif()
llvm_ExternalProject_Add(runtimes
                                       -DLLVM_DEFAULT_TARGET_TRIPLE=${LLVM_TARGET_TRIPLE}
                                       -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
                                       -DLLVM_BUILD_TOOLS=${LLVM_BUILD_TOOLS}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
+                                      ${EXTERNAL_RUNTIMES_CMAKE_ARGS}
                                       ${RUNTIMES_CMAKE_ARGS}
                                       ${ARG_CMAKE_ARGS}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                                                 LLVM_USE_LINKER
                                                 ${ARG_PREFIXES}
                            EXTRA_TARGETS ${extra_targets}
                                          ${test_targets}
                                          ${SUB_COMPONENTS}
llvm_ExternalProject_Add(runtimes-${name}
                                       -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON
                                       -DLLVM_RUNTIMES_TARGET=${name}
                                       ${COMMON_CMAKE_ARGS}
+                                      ${EXTERNAL_RUNTIMES_CMAKE_ARGS}
                                       ${${name}_extra_args}
                            EXTRA_TARGETS ${${name}_extra_targets}
                                          ${${name}_test_targets}
                            USE_TOOLCHAIN
                            ${EXTRA_ARGS} ${ARG_EXTRA_ARGS})
 endfunction()
 
 if(runtimes)

runtimes/CMakeLists.txt

foreach(proj ${LLVM_ENABLE_RUNTIMES})
   else()
     message(FATAL_ERROR "LLVM_ENABLE_RUNTIMES requests ${proj} but directory not found: ${proj_dir}")
   endif()
   string(TOUPPER "${proj}" canon_name)
   STRING(REGEX REPLACE "-" "_" canon_name ${canon_name})
   set(LLVM_EXTERNAL_${canon_name}_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../${proj}")
 endforeach()
 
+foreach(proj ${LLVM_EXTERNAL_RUNTIMES})
+  string(TOUPPER "${proj}" canon_name)
+  STRING(REGEX REPLACE "-" "_" canon_name ${canon_name})
+  set(proj_dir "${LLVM_EXTERNAL_${canon_name}_SOURCE_DIR}")
+  if(IS_DIRECTORY ${proj_dir} AND EXISTS ${proj_dir}/CMakeLists.txt)
+    list(APPEND runtimes ${proj_dir})
+  else()
+    message(FATAL_ERROR "LLVM_EXTERNAL_RUNTIMES requests ${proj} but directory not found: ${proj_dir}")
+  endif()
+endforeach()
+
 function(runtime_register_component name)
   set_property(GLOBAL APPEND PROPERTY SUB_COMPONENTS ${name})
 endfunction()
 
 find_package(LLVM PATHS "${LLVM_BINARY_DIR}" NO_DEFAULT_PATH NO_CMAKE_FIND_ROOT_PATH)
 find_package(Clang PATHS "${LLVM_BINARY_DIR}" NO_DEFAULT_PATH NO_CMAKE_FIND_ROOT_PATH)
 
 set(LLVM_THIRD_PARTY_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../third-party")