[CMake] Support building libLLVM.a archive

[phosek]

Summary

When distributing LLVM libraries as static archive, it's useful in
some cases to distribute a single combined archive rather than a
set of libraries, since users of this archive don't need to know
the dependencies between individual LLVM libraries.

[dangyi]

I'm wondering how LLVM_BUILD_LLVM_ARCHIVE interacts with LLVM_DISTRIBUTION_COMPONENTS? More specifically, can we only include a portion of LLVM libraries in libLLVM.a?

[phosek]

In D99155#2645953, @dangyi wrote:

I'm wondering how LLVM_BUILD_LLVM_ARCHIVE interacts with LLVM_DISTRIBUTION_COMPONENTS? More specifically, can we only include a portion of LLVM libraries in libLLVM.a?

llvm-archive would be in LLVM_DISTRIBUTION_COMPONENTS, we would need a separate option to select which archives are merged into libLLVM.a.

[phosek]

In D99155#2646001, @phosek wrote:

In D99155#2645953, @dangyi wrote:

I'm wondering how LLVM_BUILD_LLVM_ARCHIVE interacts with LLVM_DISTRIBUTION_COMPONENTS? More specifically, can we only include a portion of LLVM libraries in libLLVM.a?

llvm-archive would be in LLVM_DISTRIBUTION_COMPONENTS, we would need a separate option to select which archives are merged into libLLVM.a.

We could make LLVM_BUILD_LLVM_ARCHIVE either a boolean, in which case it includes everything, or a list of libraries to include, that should be a simple change.

[tstellar]

I have this uncommitted change: D95727 which updates libLLVM.so to use object libraries, would you be able to also use object libraries to avoid adding this python script?

[phosek]

In D99155#2657221, @tstellar wrote:

I have this uncommitted change: D95727 which updates libLLVM.so to use object libraries, would you be able to also use object libraries to avoid adding this python script?

Yes I think so.

[smeenai]

Is this still relevant? Requesting changes to clear my queue.

llvm/CMakeLists.txt

 else()
   option(LLVM_LINK_LLVM_DYLIB "Link tools against the libllvm dynamic library" OFF)
   option(LLVM_BUILD_LLVM_C_DYLIB "Build libllvm-c re-export library (Darwin only)" OFF)
   set(LLVM_BUILD_LLVM_DYLIB_default OFF)
   if(LLVM_LINK_LLVM_DYLIB OR LLVM_BUILD_LLVM_C_DYLIB)
     set(LLVM_BUILD_LLVM_DYLIB_default ON)
   endif()
   option(LLVM_BUILD_LLVM_DYLIB "Build libllvm dynamic library" ${LLVM_BUILD_LLVM_DYLIB_default})
+  option(LLVM_BUILD_LLVM_ARCHIVE "Build libllvm static archive" OFF)
 endif()
 
 if (LLVM_LINK_LLVM_DYLIB AND BUILD_SHARED_LIBS)
   message(FATAL_ERROR "Cannot enable BUILD_SHARED_LIBS with LLVM_LINK_LLVM_DYLIB.  We recommend disabling BUILD_SHARED_LIBS.")
 endif()
 
 option(LLVM_OPTIMIZED_TABLEGEN "Force TableGen to be built with optimization" OFF)
 if(CMAKE_CROSSCOMPILING OR (LLVM_OPTIMIZED_TABLEGEN AND (LLVM_ENABLE_ASSERTIONS OR CMAKE_CONFIGURATION_TYPES)))
if (NOT LLVM_ENABLE_IDE)
     add_llvm_install_targets(install-llvm-libraries
                              DEPENDS llvm-libraries
                              COMPONENT llvm-libraries)
   endif()
 
   get_property(LLVM_LIBS GLOBAL PROPERTY LLVM_LIBS)
   if(LLVM_LIBS)
     list(REMOVE_DUPLICATES LLVM_LIBS)
+    if(LLVM_BUILD_LLVM_ARCHIVE)
+      set(LLVM_ARCHIVE_LIBRARIES "${LLVM_LIBS}" CACHE STRING "Libraries to include in libllvm archive")
+      mark_as_advanced(LLVM_ARCHIVE_LIBRARIES)
+      set(libs "")
+      foreach(lib ${LLVM_LIBS})
+        if(lib IN_LIST LLVM_ARCHIVE_LIBRARIES)
+          list(APPEND libs "$<$<STREQUAL:$<TARGET_LINKER_FILE_SUFFIX:${lib}>,${CMAKE_STATIC_LIBRARY_SUFFIX}>:$<TARGET_LINKER_FILE:${lib}>>")
+        endif()
+      endforeach()
+      if(${CMAKE_LIBTOOL})
+        set(LIBTOOL_ARG --libtool ${CMAKE_LIBTOOL})
+      endif()
+      set(libllvm ${LLVM_LIBRARY_OUTPUT_INTDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}LLVM${CMAKE_STATIC_LIBRARY_SUFFIX})
+      add_custom_command(
+        OUTPUT ${libllvm}
+          COMMAND ${CMAKE_COMMAND} -E remove ${libllvm}
+          COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/utils/merge-archives.py --ar ${CMAKE_AR} ${LIBTOOL_ARG} -o ${libllvm} ${libs}
+      )
+      install(FILES ${libllvm} DESTINATION lib COMPONENT llvm-archive)
+      add_custom_target(llvm-archive DEPENDS ${libllvm})
+      add_llvm_install_targets(install-llvm-archive COMPONENT llvm-archive DEPENDS ${libllvm})
+      add_dependencies(install-llvm-libraries install-llvm-archive)
+      add_dependencies(install-llvm-libraries-stripped install-llvm-archive-stripped)
+    else()
       foreach(lib ${LLVM_LIBS})
         add_dependencies(llvm-libraries ${lib})
         if (NOT LLVM_ENABLE_IDE)
           add_dependencies(install-llvm-libraries install-${lib})
           add_dependencies(install-llvm-libraries-stripped install-${lib}-stripped)
         endif()
       endforeach()
     endif()
   endif()
+endif()
 
 # This must be at the end of the LLVM root CMakeLists file because it must run
 # after all targets are created.
 include(LLVMDistributionSupport)
 llvm_distribution_add_targets()
 process_llvm_pass_plugins(GEN_CONFIG)
 
 # This allows us to deploy the Universal CRT DLLs by passing -DCMAKE_INSTALL_UCRT_LIBRARIES=ON to CMake

llvm/utils/merge-archives.py

+#!/usr/bin/env python
+#===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+#===----------------------------------------------------------------------===##
+
+from argparse import ArgumentParser
+import tempfile
+import subprocess
+import sys
+
+
+def main():
+    parser = ArgumentParser(
+        description="Merge multiple archives into a single library")
+    parser.add_argument('--ar',
+                        required=True,
+                        type=str,
+                        help='The ar executable to use')
+    parser.add_argument('--libtool',
+                        required=False,
+                        type=str,
+                        help='The libtool executable to use')
+    parser.add_argument('-o',
+                        '--output',
+                        dest='output',
+                        required=True,
+                        help='The output file',
+                        type=str,
+                        action='store')
+    parser.add_argument('archives',
+                        metavar='archives',
+                        nargs='+',
+                        help='The archives to merge')
+
+    args = parser.parse_args()
+
+    if 'llvm-ar' in args.ar:
+        subprocess.check_call([args.ar, 'DqcsL', args.output] + args.archives)
+        return 0
+
+    with tempfile.TemporaryDirectory('.merge-archives') as tmpdir:
+        files = []
+        for archive in args.archives:
+            subprocess.check_call([args.ar, 'x', archive], cwd=tmpdir)
+            out = subprocess.check_output([args.ar, 't', archive])
+            files.extend(
+                [f for f in out.splitlines() if not f.startswith('__.SYMDEF')])
+
+        if args.libtool:
+            subprocess.check_call(
+                [args.libtool, '-static', '-o', args.output] + files,
+                cwd=tmpdir)
+        else:
+            subprocess.check_call([args.ar, 'Drcs', args.output] + files,
+                                  cwd=tmpdir)
+
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())