[CMake] Find python before searching for python modules

[dim]

Summary

In the top-level llvm CMakeLists.txt, we need to call
find_package(Python3) *before* including config-ix.cmake, otherwise
the latter will not be able to successfully search for python modules
using find_python_module(). Also set LLVM_MINIMUM_PYTHON_VERSION
before calling find_package(Python3), moving it to CMakeLists.txt
from HandleLLVMOptions.cmake.

[compnerd]

llvm/CMakeLists.txt

766

I'd move it to L775 since this is speaking to the find_package rather than the setting of the LLVM_MINIMUM_PYTHON_VERSION.

[dim]

Address review comments.

llvm/CMakeLists.txt

else()
   set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default OFF)
 endif()
 set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR ${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR_default} CACHE BOOL
   "Enable per-target runtimes directory")
 
 set(LLVM_PROFDATA_FILE "" CACHE FILEPATH
   "Profiling data file to use when compiling in order to improve runtime performance.")
 
+if(LLVM_INCLUDE_TESTS)
+  # Lit test suite requires at least python 3.6
+  set(LLVM_MINIMUM_PYTHON_VERSION 3.6)
+else()
+  # FIXME: it is unknown if this is the actual minimum bound
+  set(LLVM_MINIMUM_PYTHON_VERSION 3.0)
+endif()
+
+# Find python before including config-ix, since it needs to be able to search
+# for python modules.
+find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION} REQUIRED
+    COMPONENTS Interpreter)
+
 # All options referred to from HandleLLVMOptions have to be specified
 # BEFORE this include, otherwise options will not be correctly set on
 # first cmake run
 include(config-ix)
 
 # By default, we target the host, but this can be overridden at CMake
 # invocation time. Except on 64-bit AIX, where the system toolchain
 # expect 32-bit objects by default.
set(LLVM_ENABLE_NEW_PASS_MANAGER TRUE CACHE BOOL
   "Enable the new pass manager by default.")
 if(NOT LLVM_ENABLE_NEW_PASS_MANAGER)
   message(FATAL_ERROR "Enabling the legacy pass manager on the cmake level is"
                       " no longer supported.")
 endif()
 
 include(HandleLLVMOptions)
 
-find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION} REQUIRED
-    COMPONENTS Interpreter)
-
 ######
 
 # Configure all of the various header file fragments LLVM uses which depend on
 # configuration variables.
 set(LLVM_ENUM_TARGETS "")
 set(LLVM_ENUM_ASM_PRINTERS "")
 set(LLVM_ENUM_ASM_PARSERS "")
 set(LLVM_ENUM_DISASSEMBLERS "")

llvm/cmake/modules/HandleLLVMOptions.cmake

if(LLVM_USE_RELATIVE_PATHS_IN_FILES)
   else()
     set(source_root "${LLVM_MAIN_SRC_DIR}")
   endif()
   file(RELATIVE_PATH relative_root "${source_root}" "${CMAKE_BINARY_DIR}")
   append_if(SUPPORTS_FFILE_PREFIX_MAP "-ffile-prefix-map=${CMAKE_BINARY_DIR}=${relative_root}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
   append_if(SUPPORTS_FFILE_PREFIX_MAP "-ffile-prefix-map=${source_root}/=${LLVM_SOURCE_PREFIX}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
   add_flag_if_supported("-no-canonical-prefixes" NO_CANONICAL_PREFIXES)
 endif()
-
-if(LLVM_INCLUDE_TESTS)
-  # Lit test suite requires at least python 3.6
-  set(LLVM_MINIMUM_PYTHON_VERSION 3.6)
-else()
-  # FIXME: it is unknown if this is the actual minimum bound
-  set(LLVM_MINIMUM_PYTHON_VERSION 3.0)
-endif()