[SYCL][NativeCPU][CMake] Simplify OCK CMake handling (#19704)

I'm trying to make this repo more easily packaged by Linux distros, and
OCK came up in some feedback from NixOS (see linked issue).

Overall, the external dependency behavior should work as follows:

1) Use the user specified directory if given
2) If not, search the system for the dependency's install location and
use that
3) If not found, fetch it

OCK seems a bit special because installing OCK locally doesn't seem to
install any CMake files nor does it install the files required to use it
to build NativeCPU support. Seems we actually need the git tree, not the
installed result of a built OCK. Strange but let's go with it.

You can already provide a precreated clone to use to build with
`FetchContent` using `FETCHCONTENT_SOURCE_DIR_<uppercaseName>`, so there
is no need for variable to set the directory and a custom repo and tag.

Remove variables that duplicate functionality that already exists in
`FetchContent`, and add a simple search for the source directory on the
system.

Issue: #19635

---------

Signed-off-by: Sarnie, Nick <[email protected]>

Author: sarnex

llvm/lib/SYCLNativeCPUUtils/CMakeLists.txt

@@ -19,10 +19,6 @@ add_llvm_component_library(LLVMSYCLNativeCPUUtils
   ipo
   )
 
-set(OCK_SOURCE_DIR "" CACHE PATH "Root of the local checkout of the oneAPI Construction Kit")
-set(OCK_GIT_REPO "" CACHE STRING "Git repository for the oneAPI Construction Kit FetchContent")
-set(OCK_GIT_TAG "" CACHE STRING "Git tag for the oneAPI Construction Kit FetchContent")
-option(NATIVECPU_OCK_USE_FETCHCONTENT "Use FetchContent to acquire oneAPI Construction Kit source code" On)
 option(NATIVECPU_USE_OCK "Use the oneAPI Construction Kit for Native CPU" ON)
 
 # Don't fetch OCK if Native CPU is not enabled.
@@ -31,8 +27,16 @@ if(NOT "native_cpu" IN_LIST SYCL_ENABLE_BACKENDS)
 endif()
 
 if(NATIVECPU_USE_OCK)
-  if(NATIVECPU_OCK_USE_FETCHCONTENT)
-    set(OCK_GIT_INTERNAL_REPO "https://github.com/uxlfoundation/oneapi-construction-kit.git")
+  set(OCK_SEARCH_LOC "oneapi-construction-kit/compiler_passes")
+  if(NOT FETCHCONTENT_SOURCE_DIR_ONEAPI-CK)
+    find_path(OCK_SOURCE_DIR ${OCK_SEARCH_LOC} PATHS ${CMAKE_PREFIX_PATH})
+  endif()
+  if(OCK_SOURCE_DIR)
+    message(STATUS "Found system source location of oneAPI Construction Kit in ${OCK_SOURCE_DIR}")
+    set(OCK_SOURCE_DIR "${OCK_SOURCE_DIR}/${OCK_SEARCH_LOC}")
+    set(OCK_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/oneapi-construction-kit")
+  else()
+    set(OCK_GIT_REPO "https://github.com/uxlfoundation/oneapi-construction-kit.git")
     # commit d0a32d701e34b3285de7ce776ea36abfec673df7
     # Merge: a9f848e0e8 56473a8c25
     # Author: Harald van Dijk <[email protected]>
@@ -41,39 +45,31 @@ if(NATIVECPU_USE_OCK)
     #     Merge pull request #878 from hvdijk/specify-fuse-ld-lld
     #     
     #     [RefSi] Explicitly specify -fuse-ld=lld.
-    set(OCK_GIT_INTERNAL_TAG d0a32d701e34b3285de7ce776ea36abfec673df7)
-
-    # Overwrite OCK_GIT_INTERNAL_REPO/OCK_GIT_INTERNAL_TAG if the corresponding options are set
-    if(OCK_GIT_REPO)
-      set(OCK_GIT_INTERNAL_REPO "${OCK_GIT_REPO}")
-    endif()
-    if(OCK_GIT_TAG)
-      set(OCK_GIT_INTERNAL_TAG "${OCK_GIT_TAG}")
-    endif()
+    set(OCK_GIT_TAG d0a32d701e34b3285de7ce776ea36abfec673df7)
+   
     include(FetchContent)
     FetchContent_Declare(oneapi-ck
-     GIT_REPOSITORY "${OCK_GIT_INTERNAL_REPO}"
-     GIT_TAG "${OCK_GIT_INTERNAL_TAG}"
+     GIT_REPOSITORY "${OCK_GIT_REPO}"
+     GIT_TAG "${OCK_GIT_TAG}"
     )
     FetchContent_GetProperties(oneapi-ck)
     if(NOT oneapi-ck_POPULATED)
-      message(STATUS "Cloning oneAPI Construction Kit from ${OCK_GIT_INTERNAL_REPO}, tag ${OCK_GIT_INTERNAL_TAG}")
+      if(FETCHCONTENT_SOURCE_DIR_ONEAPI-CK)
+        message(STATUS "Using specified oneAPI Construction Kit repo location at ${FETCHCONTENT_SOURCE_DIR_ONEAPI-CK}")
+      else()
+        message(STATUS "Cloning oneAPI Construction Kit from ${OCK_GIT_REPO}, tag ${OCK_GIT_TAG}")
+      endif()
       FetchContent_Populate(oneapi-ck)
       message(STATUS "oneAPI Construction Kit cloned in ${oneapi-ck_SOURCE_DIR}")
-      set(OCK_SOURCE_DIR_INTERNAL ${oneapi-ck_SOURCE_DIR}/compiler_passes)
-      set(OCK_BINARY_DIR_INTERNAL ${oneapi-ck_BINARY_DIR})
+      set(OCK_SOURCE_DIR ${oneapi-ck_SOURCE_DIR}/compiler_passes)
+      set(OCK_BINARY_DIR ${oneapi-ck_BINARY_DIR})
     endif()
-  elseif(OCK_SOURCE_DIR)
-    set(OCK_SOURCE_DIR_INTERNAL "${OCK_SOURCE_DIR}/compiler_passes")
-    set(OCK_BINARY_DIR_INTERNAL "${CMAKE_CURRENT_BINARY_DIR}/oneapi-construction-kit")
-  else()
-    message(FATAL_ERROR "NATIVECPU_OCK_USE_FETCHCONTENT is Off and OCK_SOURCE_DIR not set")
   endif()
 
   set(CA_ENABLE_API "cl" CACHE STRING "" FORCE)
   add_subdirectory(
-    ${OCK_SOURCE_DIR_INTERNAL}
-    ${OCK_BINARY_DIR_INTERNAL} EXCLUDE_FROM_ALL)
+    ${OCK_SOURCE_DIR}
+    ${OCK_BINARY_DIR} EXCLUDE_FROM_ALL)
 
   install(TARGETS compiler-pipeline
   EXPORT;LLVMExports