[runtimes] Generalize how we reorder projects

[ldionne]

Summary

This way, we could use it for LLVM_ENABLE_PROJECTS too if desired.

[phosek]

runtimes/CMakeLists.txt

16

I searched for if(TARGET asan) and we don't seem to use that anywhere so I'm not sure if this comment is still true. It's possible that this is outdated and we no longer need to do this.

compiler-rt can depend on libcxx so I think it would make more sense to put compiler-rt after libcxx, we just need to check that nothing breaks if we do that.

19

I think that libc and libunwind should come before libcxxabi and libcxx since that matches how these libraries are layered.

[ldionne]

Address review comments.

[ldionne]

Rebase onto main (should fix CI)

[ldionne]

Rebase onto main for CI.

[phosek]

LGTM

[cjdb]

runtimes/CMakeLists.txt

25

This patch makes it impossible to build llvm-libgcc because LLVM_ALL_RUNTIMES deliberately doesn't include llvm-libgcc. I think this can be fixed by changing the first parameter to "${LLVM_ALL_RUNTIMES};llvm-libgcc", or by adding a variable that genuinely has all the runtimes (in reality, that would be spelt LLVM_ALL_RUNTIMES, and the current LLVM_ALL_RUNTIMES becomes LLVM_USER_ALL_RUNTIMES).

cmake/Modules/SortSubset.cmake

+# Sort a subset of a list according to the ordering in the full list.
+#
+# Given a list and a subset of that list, this function sorts the subset
+# according to the order in the full list, and returns that in the given
+# output variable.
+#
+# full_list:
+#   The list containing the desired order of elements in the sub-list.
+#
+# sub_list:
+#   A subset of the elements in `full_list`. Those elements will be sorted
+#   according to the order in `full_list`.
+#
+# out_var:
+#   A variable to store the resulting sorted sub-list in.
+function(sort_subset full_list sub_list out_var)
+  set(result "${full_list}")
+  foreach(project IN LISTS full_list)
+    if (NOT project IN_LIST sub_list)
+      list(REMOVE_ITEM result ${project})
+    endif()
+  endforeach()
+
+  set(${out_var} "${result}" PARENT_SCOPE)
+endfunction()

runtimes/CMakeLists.txt

 # This file handles building LLVM runtime sub-projects.
 cmake_minimum_required(VERSION 3.13.4)
 project(Runtimes C CXX ASM)
 
-set(LLVM_ALL_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi;libunwind;openmp")
+# Add path for custom and the LLVM build's modules to the CMake module path.
+set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
+list(INSERT CMAKE_MODULE_PATH 0
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
+  "${LLVM_COMMON_CMAKE_UTILS}"
+  "${LLVM_COMMON_CMAKE_UTILS}/Modules"
+  "${CMAKE_CURRENT_SOURCE_DIR}/../llvm/cmake"
+  "${CMAKE_CURRENT_SOURCE_DIR}/../llvm/cmake/modules"
+)
+
+# We order libraries to mirror roughly how they are layered, except that compiler-rt can depend
+# on libc++, so we put it after.
+set(LLVM_ALL_RUNTIMES "libc;libunwind;libcxxabi;libcxx;compiler-rt;openmp")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build (${LLVM_ALL_RUNTIMES}), or \"all\".")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all" )
   set(LLVM_ENABLE_RUNTIMES ${LLVM_ALL_RUNTIMES})
 endif()
-
-# Some of the runtimes will conditionally use the compiler-rt sanitizers.
-# To make this work smoothly, we ensure that compiler-rt is added first in
-# the list of sub-projects. This allows other sub-projects to have checks
-# like `if(TARGET asan)` to enable building with asan.
-if (compiler-rt IN_LIST LLVM_ENABLE_RUNTIMES)
-  list(REMOVE_ITEM LLVM_ENABLE_RUNTIMES compiler-rt)
-  if(NOT DEFINED LLVM_BUILD_COMPILER_RT OR LLVM_BUILD_COMPILER_RT)
-    list(PREPEND LLVM_ENABLE_RUNTIMES compiler-rt)
-  endif()
-endif()
-
-# If both libc++ and libc++abi are being built, always configure libc++abi before libc++.
-# This allows libc++ to depend on targets set up by libc++abi when it needs to.
-if (libcxx IN_LIST LLVM_ENABLE_RUNTIMES AND libcxxabi IN_LIST LLVM_ENABLE_RUNTIMES)
-  list(FIND LLVM_ENABLE_RUNTIMES libcxx _libcxx_index)
-  list(FIND LLVM_ENABLE_RUNTIMES libcxxabi _libcxxabi_index)
-  if (_libcxx_index LESS _libcxxabi_index)
-    list(TRANSFORM LLVM_ENABLE_RUNTIMES REPLACE "^libcxx$" "libcxxabi" AT ${_libcxx_index})
-    list(TRANSFORM LLVM_ENABLE_RUNTIMES REPLACE "^libcxxabi$" "libcxx" AT ${_libcxxabi_index})
-  endif()
-endif()
+include(SortSubset)
+sort_subset("${LLVM_ALL_RUNTIMES}" "${LLVM_ENABLE_RUNTIMES}" LLVM_ENABLE_RUNTIMES)
 
 foreach(proj ${LLVM_ENABLE_RUNTIMES})
   set(proj_dir "${CMAKE_CURRENT_SOURCE_DIR}/../${proj}")
   if(IS_DIRECTORY ${proj_dir} AND EXISTS ${proj_dir}/CMakeLists.txt)
     list(APPEND runtimes ${proj_dir})
   else()
     message(FATAL_ERROR "LLVM_ENABLE_RUNTIMES requests ${proj} but directory not found: ${proj_dir}")
   endif()
   string(TOUPPER "${proj}" canon_name)
   STRING(REGEX REPLACE "-" "_" canon_name ${canon_name})
   set(LLVM_EXTERNAL_${canon_name}_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../${proj}")
 endforeach()
 
 function(runtime_register_component name)
   set_property(GLOBAL APPEND PROPERTY SUB_COMPONENTS ${name})
 endfunction()
 
 find_package(LLVM PATHS "${LLVM_BINARY_DIR}" NO_DEFAULT_PATH NO_CMAKE_FIND_ROOT_PATH)
 find_package(Clang PATHS "${LLVM_BINARY_DIR}" NO_DEFAULT_PATH NO_CMAKE_FIND_ROOT_PATH)
 
-set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
-
-# Add path for custom and the LLVM build's modules to the CMake module path.
-list(INSERT CMAKE_MODULE_PATH 0
-  "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
-  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
-  "${LLVM_COMMON_CMAKE_UTILS}"
-  "${LLVM_COMMON_CMAKE_UTILS}/Modules"
-  "${CMAKE_CURRENT_SOURCE_DIR}/../llvm/cmake"
-  "${CMAKE_CURRENT_SOURCE_DIR}/../llvm/cmake/modules"
-)
-
 set(LLVM_THIRD_PARTY_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../third-party")
 
 # If building standalone by pointing CMake at this runtimes directory,
 # LLVM_BINARY_DIR isn't set, find_package(LLVM) will fail and these
 # intermediate paths are unset.
 if (NOT LLVM_BINARY_DIR)
   set(LLVM_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
 endif()