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I think the use of llvm-config would be outdated.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

6

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

22

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.

23

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

24

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.

25

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

26

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

-28

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.

0

Do you need to define LLVM_LIBRARY_OUTPUT_INTDIR or LLVM_SHLIB_OUTPUT_INTDIR?

[compnerd]

Thanks for the review!

CMakeLists.txt

-28

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.

0

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)
+
+  if(NOT LLVM_CONFIG_PATH)
+    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()
+  endif()
+
+  execute_process(COMMAND "${LLVM_CONFIG_PATH}" "--obj-root" "--bindir" "--src-root" "--includedir" "--libdir"
+                  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)
+  list(GET LLVM_CONFIG_OUTPUT 1 TOOLS_BINARY_DIR)
+  list(GET LLVM_CONFIG_OUTPUT 2 MAIN_SRC_DIR)
+  list(GET LLVM_CONFIG_OUTPUT 3 MAIN_INCLUDE_DIR)
+  list(GET LLVM_CONFIG_OUTPUT 4 LIBRARY_DIR)
+
+  set(LLVM_OBJ_ROOT ${OBJ_ROOT} CACHE PATH "path to LLVM build tree")
+  set(LLVM_TOOLS_BINARY_DIR ${TOOLS_BINARY_DIR} CACHE PATH "path to LLVM tools")
+  set(LLVM_MAIN_SRC_DIR ${MAIN_SRC_DIR} CACHE PATH "path to LLVM source tree")
+  set(LLVM_MAIN_INCLUDE_DIR ${MAIN_INCLUDE_DIR} CACHE PATH "path to LLVM includes")
+  set(LLVM_LIBRARY_DIR ${LIBRARY_DIR} CACHE PATH "path to LLVM libraries")
+
+  find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+
+  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(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
+
+  list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
+
+  include(AddLLVM)
+  include(TableGen)
+
+  set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}")
+
+  set(CMAKE_INCLUDE_CURRENT_DIR ON)
+  include_directories("${LLVM_BINARY_DIR}/include" "${LLVM_MAIN_INCLUDE_DIR}")
+  link_directories("${LLVM_LIBRARY_DIR}")
+
+  set(LLD_BUILT_STANDALONE TRUE)
+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})

COFF/CMakeLists.txt

 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

 
   DEPENDS
   COFFOptionsTableGen
-  intrinsics_gen
+  ${tablegen_deps}
   )

ELF/CMakeLists.txt

 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

 
   DEPENDS
   ELFOptionsTableGen
-  intrinsics_gen
+  ${tablegen_deps}
   )