Determine up front which projects are enabled.

Some projects need to add conditional dependencies on other projects.
compiler-rt is already doing this, and I attempted to add this to
debuginfo-tests when I ran into the ordering problem, that you can't
conditionally add a dependency unless that dependency's CMakeLists.txt
has already been run (which would allow you to say if (TARGET foo).

The solution to this seems to be to determine very early on the entire
set of projects which is enabled. This is complicated by the fact that
there are multiple ways to enable projects, and different tree layouts
(e.g. mono-repo, out of -tree, external, etc). This patch attempts to
centralize all of this into one place, and then updates compiler-rt to
demonstrate as a proof of concept how this can simplify code.

Differential Revision: https://reviews.llvm.org/D37637

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313091 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 52 insertions, 2 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d08fd67ddaf..cdeaf4ac706 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -823,6 +823,25 @@ endif()
 include(AddLLVM)
 include(TableGen)
 
+
+# Find all subprojects which are either enabled in a side-by-side layout, or
+# cloned into a non-side-by-side layout.  Do this before adding any
+# subdirectories so that any project can check for the existence of any other
+# project.  Each call takes priority over the next call, so any project which
+# is enabled via LLVM_ENABLE_PROJECTS will not have its location or enabled
+# status overwritten via a subsequent call.
+
+# First look for all projects explicitly enabled at the root.
+find_llvm_enabled_projects("${LLVM_SOURCE_DIR}/.." "${LLVM_ENABLE_PROJECTS}")
+
+# Then pick up any projects explicitly cloned into llvm/projects or llvm/runtimes
+find_llvm_enabled_projects("${LLVM_SOURCE_DIR}/runtimes")
+find_llvm_enabled_projects("${LLVM_SOURCE_DIR}/projects")
+
+# Then pick up a few specific projects which can be explicit cloned into llvm/tools
+find_llvm_enabled_projects("${LLVM_SOURCE_DIR}/tools" "clang;lldb;lld")
+
+
 if( MINGW )
   # People report that -O3 is unreliable on MinGW. The traditional
   # build also uses -O2 for that reason:
diff --git a/cmake/modules/AddLLVM.cmake b/cmake/modules/AddLLVM.cmake
index 66abb2486d9..a23bb263038 100644
--- a/cmake/modules/AddLLVM.cmake
+++ b/cmake/modules/AddLLVM.cmake
@@ -687,7 +687,7 @@ macro(add_llvm_executable name)
     # it forces Xcode to properly link the static library.
     list(APPEND ALL_FILES "${LLVM_MAIN_SRC_DIR}/cmake/dummy.cpp")
   endif()
-  
+
   if( EXCLUDE_FROM_ALL )
     add_executable(${name} EXCLUDE_FROM_ALL ${ALL_FILES})
   else()
@@ -920,6 +920,37 @@ function(canonicalize_tool_name name output)
   set(${output} "${nameUPPER}" PARENT_SCOPE)
 endfunction(canonicalize_tool_name)
 
+macro(find_llvm_enabled_projects base_dir)
+  set(specific_project_list "${ARGN}")
+  if("${specific_project_list}" STREQUAL "")
+    file(GLOB entries "${base_dir}/*")
+    set(list_of_project_dirs "")
+    foreach(entry ${entries})
+      if(IS_DIRECTORY ${entry} AND EXISTS ${entry}/CMakeLists.txt)
+        get_filename_component(filename "${entry}" NAME)
+        list(APPEND specific_project_list "${filename}")
+      endif()
+    endforeach(entry)
+  endif()
+
+  foreach(proj ${specific_project_list})
+    canonicalize_tool_name(${proj} projUPPER)
+
+    if (${LLVM_PROJECT_${projUPPER}_ENABLED})
+      if (EXISTS "${base_dir}/${proj}")
+        message(WARNING "Project ${projUPPER} in ${base_dir}/${proj} previously found in ${LLVM_PROJECT_${projUPPER}_SOURCE_DIR}")
+      endif()
+      continue()
+    elseif(EXISTS "${LLVM_EXTERNAL_${projUPPER}_SOURCE_DIR}")
+      set(LLVM_PROJECT_${projUPPER}_ENABLED ON)
+      set(LLVM_PROJECT_${projUPPER}_SOURCE_DIR "${LLVM_EXTERNAL_${projUPPER}_SOURCE_DIR}")
+    elseif(EXISTS "${base_dir}/${proj}")
+      set(LLVM_PROJECT_${projUPPER}_ENABLED ON)
+      set(LLVM_PROJECT_${projUPPER}_SOURCE_DIR "${base_dir}/${proj}")
+    endif()
+  endforeach()
+endmacro()
+
 # Custom add_subdirectory wrapper
 # Takes in a project name (i.e. LLVM), the subdirectory name, and an optional
 # path if it differs from the name.
@@ -1350,7 +1381,7 @@ function(add_llvm_tool_symlink link_name target)
   # magic. First we grab one of the types, and a type-specific path. Then from
   # the type-specific path we find the last occurrence of the type in the path,
   # and replace it with CMAKE_CFG_INTDIR. This allows the build step to be type
-  # agnostic again. 
+  # agnostic again.
   if(NOT ARG_OUTPUT_DIR)
     # If you're not overriding the OUTPUT_DIR, we can make the link relative in
     # the same directory.