[llvm-dev] D16945: LLVM overhaul to avoid linking LLVM component libraries with libLLVM

[Jack Howarth via llvm-dev]

Hans,
      I have posted a complete patch for solving the linkage issues
with LLVM_LINK_LLVM_DYLIB on Phabricator at
http://reviews.llvm.org/D16945.  The bulk of the fix the simple
changes of...

Index: cmake/modules/AddLLVM.cmake
===================================================================
--- cmake/modules/AddLLVM.cmake (revision 259743)
+++ cmake/modules/AddLLVM.cmake (working copy)
@@ -475,13 +475,15 @@
   # property has been set to an empty value.
   get_property(lib_deps GLOBAL PROPERTY LLVMBUILD_LIB_DEPS_${name})

-  if (LLVM_LINK_LLVM_DYLIB AND NOT ARG_STATIC AND NOT
ARG_DISABLE_LLVM_LINK_LLVM_DYLIB)
-    set(llvm_libs LLVM)
-  else()
-    llvm_map_components_to_libnames(llvm_libs
-      ${ARG_LINK_COMPONENTS}
-      ${LLVM_LINK_COMPONENTS}
-      )
+  if (DEFINED LLVM_LINK_COMPONENTS OR DEFINED ARG_LINK_COMPONENTS)
+    if (LLVM_LINK_LLVM_DYLIB AND NOT ARG_DISABLE_LLVM_LINK_LLVM_DYLIB)
+      set(llvm_libs LLVM)
+    else()
+      llvm_map_components_to_libnames(llvm_libs
+        ${ARG_LINK_COMPONENTS}
+        ${LLVM_LINK_COMPONENTS}
+        )
+    endif()
   endif()

   if(CMAKE_VERSION VERSION_LESS 2.8.12)
Index: cmake/modules/LLVM-Config.cmake
===================================================================
--- cmake/modules/LLVM-Config.cmake     (revision 259743)
+++ cmake/modules/LLVM-Config.cmake     (working copy)
@@ -40,10 +40,17 @@
     # done in case libLLVM does not contain all of the components
     # the target requires.
     #
-    # TODO strip LLVM_DYLIB_COMPONENTS out of link_components.
+    # Strip LLVM_DYLIB_COMPONENTS out of link_components.
     # To do this, we need special handling for "all", since that
     # may imply linking to libraries that are not included in
     # libLLVM.
+    if (DEFINED link_components AND DEFINED LLVM_DYLIB_COMPONENTS)
+      if("${LLVM_DYLIB_COMPONENTS}" STREQUAL "all")
+        set(link_components "")
+      else()
+        list(REMOVE_ITEM link_components ${LLVM_DYLIB_COMPONENTS})
+      endif()
+    endif()
     target_link_libraries(${executable} LLVM)
   endif()

However the avoiding the accidental linkage of libLLVMSupport with
libLLVM and libgtest for the unittests was really tricky as two
different mechanisms to pass LLVMSupport are in play.  The underlying
problem was that the python based llvm-build tool was forcing a
dependency on LLVMSupport for libgtest according to the
required_libraries entry for the gtest library in
utils/unittest/LLVMBuild.txt.  Since the llvm-build tool has no access
to the cmake defines, I had to solve this problem by adding a new
--enable-llvm-link-llvm-dylib option in
utils/llvm-build/llvmbuild/main.py to allow the LLVM_LINK_LLVM_DYLIB
build to prune 'Support' from the the required library dependencies of
the gtest library before the creation of
tools/llvm-config/LibraryDependencies.inc. Now the
LLVM_LINK_LLVM_DYLIB build contains...

{ "gtest", "libgtest.a", false, { } },

rather than

{ "gtest", "libgtest.a", false, { "support" } },

in that file.  If there are specific maintainers for the llvm-build
code, please add them to the review.
          Thanks in advance.
               Jack