CMake: Replace open-coded find_package

[chapuni]

I suggest this may be an options when LLVM_CONFIG is not specified.

CMakeLists.txt

36 ↗

(On Diff #96859)

Could we move find_package(LLVM) into here?

[chapuni]

I have investigated what LLVMConfig.cmake actually provides.

With the installed tree, SRC_ROOT (LLVM_BUILD_MAIN_SRC_DIR) is not provided.
It shouldn't be included in installed LLVMConfig.cmake. Just "llvm-config --src-root" knows. And LLVM_MAIN_SRC_DIR should be CACHE, optional to be specified manually.

I suggest;

1. Invoke "llvm-config --cmakedir --src-root" if LLVM_CONFIG is specified. (may be removed in future) Do not override LLVM_MAIN_SRC_DIR if it is defined.
2. find_package(LLVM REQUIRED HINTS ${LLVM_CMAKE_PATH}). Without LLVM_CONFIG, CMake will seek LLVMConfig.cmake along CMake's search paths like -DCMAKE_PREFIX_PATH.
3. If LLVM_MAIN_SRC_DIR is unknown, invoke "llvm-config --src-root"

LLVM_MAIN_SRC_DIR is just required to build test tools in llvm/utils.

[tstellar]

In D32577#739097, @chapuni wrote:

I suggest this may be an options when LLVM_CONFIG is not specified.

This is my eventual goal, but for now this is just a NFC clean up to make future changes more simple.

[tstellar]

Rebased this patch on ToT.

[tstellar]

Rebase on trunk.

[mgorny]

LGTM

cfe/trunk/CMakeLists.txt

if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
 
   # Normalize LLVM_CMAKE_PATH. --cmakedir might contain backslashes.
   # CMake assumes slashes as PATH.
   file(TO_CMAKE_PATH ${LLVM_CONFIG_CMAKE_PATH} LLVM_CMAKE_PATH)
 
   find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR}
     NO_DEFAULT_PATH)
 
-  set(LLVMCONFIG_FILE "${LLVM_CMAKE_PATH}/LLVMConfig.cmake")
-  if(EXISTS ${LLVMCONFIG_FILE})
-    list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
-    include(${LLVMCONFIG_FILE})
-  else()
-    message(FATAL_ERROR "Not found: ${LLVMCONFIG_FILE}")
-  endif()
+  find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_PATH}")
+  list(APPEND CMAKE_MODULE_PATH ${LLVM_DIR})
 
   # They are used as destination of target generators.
   set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
   set(LLVM_LIBRARY_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})
   if(WIN32 OR CYGWIN)
     # DLL platform -- put DLLs into bin.
     set(LLVM_SHLIB_OUTPUT_INTDIR ${LLVM_RUNTIME_OUTPUT_INTDIR})
   else()