[CMake][compiler-rt] Don't load LLVM config in the runtimes build

[phosek]

Summary

LLVM runtimes build already loads the LLVM config and sets all
appropriate variables, no need to do it again.

[mstorsjo]

compiler-rt/CMakeLists.txt

82–84

Isn’t this condition unnecessary? This is in a block guarded with if (COMPILER_RT_STANDALONE_BUILD), and if that’s true, LLVM_RUNTIMES_BUILD won’t be set?

compiler-rt/lib/builtins/CMakeLists.txt

28–30

Ditto here?

[phosek]

compiler-rt/CMakeLists.txt

82–84

We currently set COMPILER_RT_STANDALONE_BUILD in the runtimes build, see https://github.com/llvm/llvm-project/blob/f53fde8e150553c194b3325fe2781775aa40ac3a/runtimes/CMakeLists.txt#L183. I'd like to eventually remove that, but we need to do a bunch of cleanup first.

[mstorsjo]

compiler-rt/CMakeLists.txt

82–84

Ah, I see.

Ok, in that case, this is a step in the right direction indeed. And I can see that it'll take a couple patches to untangle it - the compiler-rt cmake files are notoriously complex.

[phosek]

compiler-rt/CMakeLists.txt

82–84

Yeah, I'd like to improve the runtimes build support in compiler-rt with the eventual goal of deprecating the standalone build the same way we've done for libc++, but that's difficult if we have to make all changes in a way that doesn't break the standalone build. So I'm thinking about taking a different strategy which is to put the integration behind LLVM_RUNTIMES_BUILD until we're ready to deprecate the standalone build. It's not the cleanest solution, but hopefully it's just temporary.

[mgorny]

Thanks for the explanation. This indeed makes sense then. Perhaps leave an explanatory comment/FIXME above it, so we know why it's like that in the future.

[mstorsjo]

compiler-rt/CMakeLists.txt

82–84

Sounds reasonable, as long as there’s a simple way to only build the builtins. IIRC llvm/runtimes builds those in a separate pass before building all other runtimes?

Currently in my bootstraps, I build the builtins in a super-standalone way by pointing cmake at compiler-rt/lib/builtins.

[phosek]

compiler-rt/CMakeLists.txt

82–84

We use the same approach in the bootstrapping build: https://github.com/llvm/llvm-project/blob/d6494524490e0d4ffb99dcf21d633c11108b6bf6/llvm/runtimes/CMakeLists.txt#L107

compiler-rt/CMakeLists.txt

 set(COMPILER_RT_BAREMETAL_BUILD OFF CACHE BOOL
   "Build for a bare-metal target.")
 
 if (COMPILER_RT_STANDALONE_BUILD)
   set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
   set(CMAKE_CXX_STANDARD_REQUIRED YES)
   set(CMAKE_CXX_EXTENSIONS NO)
 
+  if (NOT LLVM_RUNTIMES_BUILD)
     load_llvm_config()
+  endif()
   if (TARGET intrinsics_gen)
     # Loading the llvm config causes this target to be imported so place it
     # under the appropriate folder in an IDE.
     set_target_properties(intrinsics_gen PROPERTIES FOLDER "Compiler-RT Misc")
   endif()
 
   find_package(Python3 COMPONENTS Interpreter)
   if(NOT Python3_Interpreter_FOUND)

compiler-rt/lib/builtins/CMakeLists.txt

list(INSERT CMAKE_MODULE_PATH 0
     "${COMPILER_RT_SOURCE_DIR}/cmake/Modules"
     "${LLVM_COMMON_CMAKE_UTILS}"
     "${LLVM_COMMON_CMAKE_UTILS}/Modules"
     )
 
   include(base-config-ix)
   include(CompilerRTUtils)
 
+  if (NOT LLVM_RUNTIMES_BUILD)
     load_llvm_config()
+  endif()
   construct_compiler_rt_default_triple()
 
   include(SetPlatformToolchainTools)
   if(APPLE)
     include(CompilerRTDarwinUtils)
   endif()
   if(APPLE)
     include(UseLibtool)

runtimes/CMakeLists.txt

 # 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()
 if (NOT LLVM_FOUND)
   set(LLVM_TOOLS_BINARY_DIR ${LLVM_BINARY_DIR}/bin)
+  set(LLVM_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include)
   set(LLVM_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR}/lib)
 endif()
 
 # Setting these variables will allow the sub-build to put their outputs into
 # the library and bin directories of the top-level build.
 set(LLVM_LIBRARY_OUTPUT_INTDIR ${LLVM_LIBRARY_DIR})
 set(LLVM_RUNTIME_OUTPUT_INTDIR ${LLVM_TOOLS_BINARY_DIR})