[CMake] Add `CLANG_ENABLE_HLSL` CMake option

[beanz]

Summary

The HLSL support in clang is in proress and not fully functioning. As
such we don't want to install the related optional build components by
default (yet), but we do need an option to build and install them
locally for testing and for some key users.

This adds the CLANG_ENABLE_HLSL option which is off by default and can
be enabled to install the HLSL clang headers and the clang-dxc symlink.

[phosek]

LGTM (there's a typo in your summary in case you use it for the commit message: "proress" instead of "progress").

clang/CMakeLists.txt

set(LIBCLANG_LIBRARY_VERSION
     "${CLANG_VERSION_MAJOR}" CACHE STRING
     "Major version number that will be appended to the libclang library")
 mark_as_advanced(CLANG_EXECUTABLE_VERSION LIBCLANG_LIBRARY_VERSION)
 
 option(CLANG_INCLUDE_TESTS
        "Generate build targets for the Clang unit tests."
        ${LLVM_INCLUDE_TESTS})
 
+option(CLANG_ENABLE_HLSL "Include HLSL build products" Off)
+# While HLSL support is experimental this should stay hidden.
+mark_as_advanced(CLANG_ENABLE_HLSL)
+
 add_subdirectory(utils/TableGen)
 
 # Export CLANG_TABLEGEN_EXE for use by flang docs.
 set(CLANG_TABLEGEN_EXE "${CLANG_TABLEGEN_EXE}" CACHE INTERNAL "")
 
 add_subdirectory(include)
 
 # All targets below may depend on all tablegen'd files.

clang/cmake/caches/HLSL.cmake

 # Including the native target is important because some of LLVM's tests fail if
 # you don't.
 set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
 
 # Include the DirectX target for DXIL code generation, eventually we'll include
 # SPIR-V here too.
 set(LLVM_EXPERIMENTAL_TARGETS_TO_BUILD DirectX CACHE STRING "")
 
 # HLSL support is currently limted to clang, eventually it will expand to
 # clang-tools-extra too.
 set(LLVM_ENABLE_PROJECTS "clang" CACHE STRING "")
+
+set(CLANG_ENABLE_HLSL On CACHE BOOL "")

clang/lib/Headers/CMakeLists.txt

 
 set(hip_files
   __clang_hip_libdevice_declares.h
   __clang_hip_cmath.h
   __clang_hip_math.h
   __clang_hip_runtime_wrapper.h
   )
 
-set(hlsl_files
-  hlsl.h
+set(hlsl_h hlsl.h)
+set(hlsl_subdir_files
   hlsl/hlsl_basic_types.h
   hlsl/hlsl_intrinsics.h
   )
+set(hlsl_files
+  ${hlsl_h}
+  ${hlsl_subdir_files}
+  )
 
 set(mips_msa_files
   msa.h
   )
 
 set(opencl_files
   opencl-c.h
   opencl-c-base.h
install(
   COMPONENT webassembly-resource-headers)
 
 install(
   FILES ${x86_files}
   DESTINATION ${header_install_dir}
   EXCLUDE_FROM_ALL
   COMPONENT x86-resource-headers)
 
+if(NOT CLANG_ENABLE_HLSL)
+  set(EXCLUDE_HLSL EXCLUDE_FROM_ALL)
+endif()
+
 install(
-  FILES ${hlsl_files}
+  FILES ${hlsl_h}
   DESTINATION ${header_install_dir}
-  EXCLUDE_FROM_ALL
+  ${EXCLUDE_HLSL}
+  COMPONENT hlsl-resource-headers)
+
+install(
+  FILES ${hlsl_subdir_files}
+  DESTINATION ${header_install_dir}/hlsl
+  ${EXCLUDE_HLSL}
   COMPONENT hlsl-resource-headers)
 
 install(
   FILES ${opencl_files}
   DESTINATION ${header_install_dir}
   EXCLUDE_FROM_ALL
   COMPONENT opencl-resource-headers)
 

clang/tools/driver/CMakeLists.txt

 endif()
 
 add_dependencies(clang clang-resource-headers)
 
 if(NOT CLANG_LINKS_TO_CREATE)
   set(CLANG_LINKS_TO_CREATE clang++ clang-cl clang-cpp)
 endif()
 
-foreach(link ${CLANG_LINKS_TO_CREATE})
+if (CLANG_ENABLE_HLSL)
+  set(HLSL_LINK clang-dxc)
+endif()
+
+foreach(link ${CLANG_LINKS_TO_CREATE} ${HLSL_LINK})
   add_clang_symlink(${link} clang)
 endforeach()
 
 # Configure plist creation for OS X.
 set (TOOL_INFO_PLIST "Info.plist" CACHE STRING "Plist name")
 if (APPLE)
   if (CLANG_VENDOR)
     set(TOOL_INFO_NAME "${CLANG_VENDOR} clang")