[runtimes][NFC] Colocate handling of LLVM_ENABLE_PROJECTS and LLVM_ENABLE_RUNTIMES

[ldionne]

Summary

This will make the following patches to migrate projects off of the
LLVM_ENABLE_PROJECTS build onto the LLVM_ENABLE_RUNTIMES build much
easier to comprehend. This patch should be a NFC since it keeps the
same set of runtimes being built by default.

[ldionne]

Make llvm/CMakeLists.txt and runtimes/CMakeLists.txt consistent, and stop lying in runtimes/CMakeLists.txt (the option documentation did not reflect what we really did).

[Ericson2314]

So this is in preparation for LLVM_DEFAULT_RUNTIMES in llvm/CMakeLists.txt doing a runtimes/ instead of llvm/runtimes/ build (among other changes)?

[ldionne]

In D132478#3743644, @Ericson2314 wrote:

So this is in preparation for LLVM_DEFAULT_RUNTIMES in llvm/CMakeLists.txt doing a runtimes/ instead of llvm/runtimes/ build (among other changes)?

No, that doesn't change. We currently have two places where we define the set of things valid inside LLVM_ENABLE_RUNTIMES: <root>/runtimes/CMakeLists.txt and <root>/llvm/runtimes/CMakeLists.txt. This makes the two of them consistent, and also moves the one in <root>/llvm/runtimes/CMakeLists.txt to <root>/llvm/CMakeLists.txt so it can be close to the place where we define LLVM_ENABLE_PROJECTS, since the two are strongly related.

[Ericson2314]

Ah right, runtimes/ and llvm/runtimes are the two ways that remain per the plan.

It is generally nice to more narrowly "scope" LLVM_DEFAULT_RUNTIMES to where it is used, but I do see the concrete benefits when you are shuffling things between the lists.

[phosek]

LGTM

llvm/CMakeLists.txt

if (NOT "mlir" IN_LIST LLVM_ENABLE_PROJECTS)
     list(APPEND LLVM_ENABLE_PROJECTS "mlir")
   endif()
 
   if (NOT "clang" IN_LIST LLVM_ENABLE_PROJECTS)
     message(FATAL_ERROR "Clang is not enabled, but is required for the Flang driver")
   endif()
 endif()
 
+# Select the runtimes to build
+set(LLVM_DEFAULT_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi;libunwind;openmp")
+set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc")
+set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
+  "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
+if(LLVM_ENABLE_RUNTIMES STREQUAL "all")
+  set(LLVM_ENABLE_RUNTIMES ${LLVM_DEFAULT_RUNTIMES})
+endif()
+foreach(proj IN LISTS LLVM_ENABLE_RUNTIMES)
+  if (NOT "${proj}" IN_LIST LLVM_SUPPORTED_RUNTIMES)
+    message(FATAL_ERROR "Runtime ${proj} is not a supported runtime. Supported runtimes are: ${LLVM_SUPPORTED_RUNTIMES}")
+  endif()
+endforeach()
+
 # LLVM_ENABLE_PROJECTS_USED is `ON` if the user has ever used the
 # `LLVM_ENABLE_PROJECTS` CMake cache variable.  This exists for
 # several reasons:
 #
 # * As an indicator that the `LLVM_ENABLE_PROJECTS` list is now the single
 # source of truth for which projects to build. This means we will ignore user
 # supplied `LLVM_TOOL_<project>_BUILD` CMake cache variables and overwrite
 # them.

llvm/runtimes/CMakeLists.txt

 # TODO: This file assumes the Clang toolchain so it'd be better if it lived in
 # Clang, except there already is clang/runtime directory which contains
 # similar although simpler functionality. We should figure out how to merge
 # the two files.
 
-# TODO: Selecting runtimes should be always performed inside the runtimes
-# build, see runtimes/CMakeLists.txt, except that we currently check whether
-# compiler-rt is being built to determine whether to first build builtins
-# or not so we need that information in this file as well.
-set(LLVM_ALL_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi;libunwind;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()
 set(COMMON_CMAKE_ARGS "-DHAVE_LLVM_LIT=ON")
 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()

runtimes/CMakeLists.txt

list(INSERT CMAKE_MODULE_PATH 0
   "${LLVM_COMMON_CMAKE_UTILS}/Modules"
   "${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_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp")
-set(LLVM_ALL_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc")
+set(LLVM_SUPPORTED_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
-  "Semicolon-separated list of runtimes to build (${LLVM_ALL_RUNTIMES}), or \"all\".")
+  "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all" )
   set(LLVM_ENABLE_RUNTIMES ${LLVM_DEFAULT_RUNTIMES})
 endif()
 include(SortSubset)
-sort_subset("${LLVM_ALL_RUNTIMES}" "${LLVM_ENABLE_RUNTIMES}" LLVM_ENABLE_RUNTIMES)
+sort_subset("${LLVM_SUPPORTED_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()