[projects] Use add_llvm_external_project for implicit projects

[smeenai]

Summary

This allows disabling implicit projects via the LLVM_TOOL_*_BUILD
variables, similar to how implicit tools can be disabled. They'll still
be enabled by default, since add_llvm_external_project defaults the
LLVM_TOOL_*_BUILD variables to ON for in-tree implciit projects.

[smeenai]

Correct patch

[smeenai]

Testing

[phosek]

LGTM

llvm/cmake/modules/AddLLVM.cmake

function(canonicalize_tool_name name output)
   string(REPLACE "-" "_" nameUNDERSCORE ${nameStrip})
   string(TOUPPER ${nameUNDERSCORE} nameUPPER)
   set(${output} "${nameUPPER}" PARENT_SCOPE)
 endfunction(canonicalize_tool_name)
 
 # 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.
-macro(add_llvm_subdirectory project type name)
+function(add_llvm_subdirectory project type name)
   set(add_llvm_external_dir "${ARGN}")
   if("${add_llvm_external_dir}" STREQUAL "")
     set(add_llvm_external_dir ${name})
   endif()
   canonicalize_tool_name(${name} nameUPPER)
+  set(canonical_full_name ${project}_${type}_${nameUPPER})
+  get_property(already_processed GLOBAL PROPERTY ${canonical_full_name}_PROCESSED)
+  if(already_processed)
+    return()
+  endif()
+  set_property(GLOBAL PROPERTY ${canonical_full_name}_PROCESSED YES)
+
   if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${add_llvm_external_dir}/CMakeLists.txt)
     # Treat it as in-tree subproject.
-    option(${project}_${type}_${nameUPPER}_BUILD
+    option(${canonical_full_name}_BUILD
            "Whether to build ${name} as part of ${project}" On)
     mark_as_advanced(${project}_${type}_${name}_BUILD)
-    if(${project}_${type}_${nameUPPER}_BUILD)
+    if(${canonical_full_name}_BUILD)
       add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${add_llvm_external_dir} ${add_llvm_external_dir})
-      # Don't process it in add_llvm_implicit_projects().
-      set(${project}_${type}_${nameUPPER}_BUILD OFF)
     endif()
   else()
     set(LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR
       "${LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR}"
       CACHE PATH "Path to ${name} source directory")
-    set(${project}_${type}_${nameUPPER}_BUILD_DEFAULT ON)
+    set(${canonical_full_name}_BUILD_DEFAULT ON)
     if(NOT LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR OR NOT EXISTS ${LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR})
-      set(${project}_${type}_${nameUPPER}_BUILD_DEFAULT OFF)
+      set(${canonical_full_name}_BUILD_DEFAULT OFF)
     endif()
     if("${LLVM_EXTERNAL_${nameUPPER}_BUILD}" STREQUAL "OFF")
-      set(${project}_${type}_${nameUPPER}_BUILD_DEFAULT OFF)
+      set(${canonical_full_name}_BUILD_DEFAULT OFF)
     endif()
-    option(${project}_${type}_${nameUPPER}_BUILD
+    option(${canonical_full_name}_BUILD
       "Whether to build ${name} as part of LLVM"
-      ${${project}_${type}_${nameUPPER}_BUILD_DEFAULT})
-    if (${project}_${type}_${nameUPPER}_BUILD)
+      ${${canonical_full_name}_BUILD_DEFAULT})
+    if (${canonical_full_name}_BUILD)
       if(EXISTS ${LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR})
         add_subdirectory(${LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR} ${add_llvm_external_dir})
       elseif(NOT "${LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR}" STREQUAL "")
         message(WARNING "Nonexistent directory for ${name}: ${LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR}")
       endif()
-      # FIXME: It'd be redundant.
-      set(${project}_${type}_${nameUPPER}_BUILD Off)
     endif()
   endif()
-endmacro()
+endfunction()
 
 # Add external project that may want to be built as part of llvm such as Clang,
 # lld, and Polly. This adds two options. One for the source directory of the
 # project, which defaults to ${CMAKE_CURRENT_SOURCE_DIR}/${name}. Another to
 # enable or disable building it with everything else.
 # Additional parameter can be specified as the name of directory.
 macro(add_llvm_external_project name)
   add_llvm_subdirectory(LLVM TOOL ${name} ${ARGN})

llvm/projects/CMakeLists.txt

 # Discover the projects that use CMake in the subdirectories.
 # Note that explicit cmake invocation is required every time a new project is
 # added or removed.
 file(GLOB entries *)
 foreach(entry ${entries})
   if(IS_DIRECTORY ${entry} AND EXISTS ${entry}/CMakeLists.txt)
     if((NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/compiler-rt) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/dragonegg) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/libcxx) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/libcxxabi) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/libunwind) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/test-suite) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/parallel-libs) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/openmp) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/debuginfo-tests))
-      add_subdirectory(${entry})
+      add_llvm_external_project(${entry})
     endif()
   endif()
 endforeach(entry)
 
 # Also add in libc++ and compiler-rt trees if present (and we have
 # a sufficiently recent version of CMake where required).
 if(${LLVM_BUILD_RUNTIME})
   # MSVC isn't quite working with libc++ yet, disable it until issues are