build: add support for standalone lld build

[compnerd]

Summary

Enable building lld as a standalone project. This is motivated by the desire to package lld for inclusion in a linux distribution. This allows building lld against an existing paired llvm installation. Now that lld is usable on x86_64, it makes sense to revive this configuration to allow distributions to package it.

[ruiu]

I'm not very familiar with the build system. Can Clang be built as a standalone project?

[compnerd]

@ruiu, yes, clang and lldb can both be built in the standalone configuration.

[ruiu]

Me too. LGTM but please get a review from someone who knows CMake well.

[chapuni]

I think the use of llvm-config would be outdated. (Clang's should be rewritten)
That said, I have no idea what would be better as modern CMake.

I implemented such a snippet to clang before Brad King started to advise us.

That said, I think this may be fed to trunk atm if this just works. Delegating to Chris.

[davide]

Can you please update again with context? @Bigcheese/@beanz are probably in a good position to review this.

[mgorny]

CMakeLists.txt

156

Is there a reason for an additional conditional like this? find_program makes LLVM_CONFIG_PATH a cache variable, so I think this would be cleaner without the outer conditional.

[beanz]

Mostly this patch LGTM, but I'd like to make a few minor tweaks to modernize it a bit. Comments below.

[beanz]

CMakeLists.txt

172

I think this is the only variable from llvm-config that you need. The others can all be read from LLVMConfig.cmake.

Even this one we could potentially get rid of if we made use of CMake's find_package mechanism.

173

This is equivalent to LLVM_TOOLS_BINARY_DIR which is set in LLVMConfig.cmake.

174

If you're building against a build tree, instead of an install, this is exposed as LLVM_BUILD_MAIN_SRC_DIR in LLVMConfig.cmake. If you're not building against a build tree, we actually don't know if you have a source dir, so there is no path.

175

This is equivalent to LLVM_INCLUDE_DIRS which is set in LLVMConfig.cmake.

176

This is equivalent to LLVM_LIBRARY_DIRS which is set in LLVMConfig.cmake.

[Eugene.Zelenko]

In D27386#612797, @compnerd wrote:

@ruiu, yes, clang and lldb can both be built in the standalone configuration.

Unfortunately standalone LLDB build was broken recently. See PR31104.

[beanz]

In D27386#613569, @Eugene.Zelenko wrote:

Unfortunately standalone LLDB build was broken recently. See PR31104.

LLDB should be fixed in r288691.

[compnerd]

Address comments from @beanz and @mgrony

[beanz]

One minor nit below, and a question. Otherwise LGTM!

CMakeLists.txt

16

Since you're only outputting one field now you should be able to just write the result directly into OBJ_ROOT. Then you can get rid of the string processing below.

44

Do you need to define LLVM_LIBRARY_OUTPUT_INTDIR or LLVM_SHLIB_OUTPUT_INTDIR?

[compnerd]

Thanks for the review!

CMakeLists.txt

16

Sure, Ill simplify it. I thought keeping it generic would be good. But, given that we want to modernise the usage here, it makes sense to simplify and then replace it across all the projects.

44

It wouldnt hurt to define them, however, they are not currently used by the lld build afaik.

[compnerd]

SVN r289421.

Had to undo the simplification because the include dir needs to be added (as discussed offline with @beanz).

CMakeLists.txt

+# Check if lld is built as a standalone project.
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  project(lld)
+  cmake_minimum_required(VERSION 3.4.3)
+
+  set(CMAKE_INCLUDE_CURRENT_DIR ON)
+  set(LLD_BUILT_STANDALONE TRUE)
+
+  find_program(LLVM_CONFIG_PATH "llvm-config" DOC "Path to llvm-config binary")
+  if(NOT LLVM_CONFIG_PATH)
+    message(FATAL_ERROR "llvm-config not found: specify LLVM_CONFIG_PATH")
+  endif()
+
+  execute_process(COMMAND "${LLVM_CONFIG_PATH}" "--obj-root"
+                  RESULT_VARIABLE HAD_ERROR
+                  OUTPUT_VARIABLE LLVM_CONFIG_OUTPUT
+                  OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(HAD_ERROR)
+    message(FATAL_ERROR "llvm-config failed with status ${HAD_ERROR}")
+  endif()
+
+  string(REGEX REPLACE "[ \t]*[\r\n]+[ \t]*" ";" LLVM_CONFIG_OUTPUT ${LLVM_CONFIG_OUTPUT})
+  list(GET LLVM_CONFIG_OUTPUT 0 OBJ_ROOT)
+
+  set(LLVM_OBJ_ROOT ${OBJ_ROOT} CACHE PATH "path to LLVM build tree")
+
+  file(TO_CMAKE_PATH ${LLVM_OBJ_ROOT} LLVM_BINARY_DIR)
+  set(LLVM_CMAKE_PATH "${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/cmake/llvm")
+
+  if(NOT EXISTS "${LLVM_CMAKE_PATH}/LLVMConfig.cmake")
+    message(FATAL_ERROR "LLVMConfig.cmake not found")
+  endif()
+  include("${LLVM_CMAKE_PATH}/LLVMConfig.cmake")
+
+  set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}")
+  include_directories("${LLVM_BINARY_DIR}/include" ${LLVM_INCLUDE_DIRS})
+  link_directories(${LLVM_LIBRARY_DIRS})
+
+  list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
+
+  include(AddLLVM)
+  include(TableGen)
+
+  set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
+  find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+endif()
+
 set(LLD_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 set(LLD_INCLUDE_DIR ${LLD_SOURCE_DIR}/include )
 set(LLD_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
 
 # Compute the LLD version from the LLVM version.
 string(REGEX MATCH "[0-9]+\\.[0-9]+(\\.[0-9]+)?" LLD_VERSION
   ${PACKAGE_VERSION})
 message(STATUS "LLD version: ${LLD_VERSION}")

 
 if (LLVM_INCLUDE_TESTS)
   add_subdirectory(test)
   add_subdirectory(unittests)
 endif()
 
 add_subdirectory(docs)
 add_subdirectory(COFF)
 add_subdirectory(ELF)

COFF/CMakeLists.txt

 set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(COFFOptionsTableGen)
 
+if(NOT LLD_BUILT_STANDALONE)
+  set(tablegen_deps intrinsics_gen)
+endif()
+
 add_lld_library(lldCOFF
   Chunks.cpp
   DLL.cpp
   Driver.cpp
   DriverUtils.cpp
   Error.cpp
   ICF.cpp
   InputFiles.cpp
add_lld_library(lldCOFF
   Support
 
   LINK_LIBS
   lldCore
   ${PTHREAD_LIB}
 
   DEPENDS
   COFFOptionsTableGen
-  intrinsics_gen
+  ${tablegen_deps}
   )

ELF/CMakeLists.txt

 set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(ELFOptionsTableGen)
 
+if(NOT LLD_BUILT_STANDALONE)
+  set(tablegen_deps intrinsics_gen)
+endif()
+
 add_lld_library(lldELF
   Driver.cpp
   DriverUtils.cpp
   EhFrame.cpp
   Error.cpp
   GdbIndex.cpp
   ICF.cpp
   InputFiles.cpp
add_lld_library(lldELF
 
   LINK_LIBS
   lldConfig
   lldCore
   ${PTHREAD_LIB}
 
   DEPENDS
   ELFOptionsTableGen
-  intrinsics_gen
+  ${tablegen_deps}
   )