CMake: Use find_package(Python3) (#6675)

Fixes the CMake CMP0148 warning at configure time.

find_package(Python3) is supported since CMake 3.12, and DXC requires at
least CMake 3.17

CMakeLists.txt

@@ -447,7 +447,7 @@ set(TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
 include(HandleLLVMOptions)
 
 # Verify that we can find a Python 3 interpreter and force cmake to use it.
-find_package(PythonInterp 3 REQUIRED)
+find_package(Python3 REQUIRED)
 
 ######
 # LLVMBuild Integration
@@ -481,7 +481,7 @@ endif (LLVM_USE_OPROFILE)
 message(STATUS "Constructing LLVMBuild project information")
 
 execute_process(
-  COMMAND ${PYTHON_EXECUTABLE} ${LLVMBUILDTOOL}
+  COMMAND ${Python3_EXECUTABLE} ${LLVMBUILDTOOL}
             --native-target Unknown
             --enable-targets "${LLVM_TARGETS_TO_BUILD}"
             --enable-optional-components "${LLVMOPTIONALCOMPONENTS}"

cmake/modules/AddLLVM.cmake

@@ -1,5 +1,6 @@
 include(LLVMProcessSources)
 include(LLVM-Config)
+find_package(Python3 REQUIRED)
 
 function(llvm_update_compile_flags name)
   get_property(sources TARGET ${name} PROPERTY SOURCES)
@@ -107,7 +108,7 @@ function(add_llvm_symbol_exports target_name export_file)
     set(native_export_file "${target_name}.def")
 
     add_custom_command(OUTPUT ${native_export_file}
-      COMMAND ${PYTHON_EXECUTABLE} -c "import sys;print(''.join(['EXPORTS\\n']+sys.stdin.readlines(),))"
+      COMMAND ${Python3_EXECUTABLE} -c "import sys;print(''.join(['EXPORTS\\n']+sys.stdin.readlines(),))"
         < ${export_file} > ${native_export_file}
       DEPENDS ${export_file}
       VERBATIM
@@ -867,7 +868,6 @@ function(configure_lit_site_cfg input output)
   # SHLIBDIR points the build tree.
   string(REPLACE ${CMAKE_CFG_INTDIR} ${LLVM_BUILD_MODE} SHLIBDIR "${LLVM_SHLIB_OUTPUT_INTDIR}")
 
-  set(PYTHON_EXECUTABLE ${PYTHON_EXECUTABLE})
   # FIXME: "ENABLE_SHARED" doesn't make sense, since it is used just for
   # plugins. We may rename it.
   if(LLVM_ENABLE_PLUGINS)
@@ -902,7 +902,7 @@ function(add_lit_target target comment)
     list(APPEND LIT_ARGS --param build_mode=${CMAKE_CFG_INTDIR})
   endif ()
   if (LLVM_MAIN_SRC_DIR)
-    set (LIT_COMMAND ${PYTHON_EXECUTABLE} ${LLVM_MAIN_SRC_DIR}/utils/lit/lit.py)
+    set (LIT_COMMAND ${Python3_EXECUTABLE} ${LLVM_MAIN_SRC_DIR}/utils/lit/lit.py)
   else()
     find_program(LIT_COMMAND llvm-lit)
   endif ()

cmake/modules/HCT.cmake

@@ -101,7 +101,7 @@ function(add_hlsl_hctgen mode)
   endif()
 
   add_custom_command(OUTPUT ${temp_output}
-                     COMMAND ${PYTHON_EXECUTABLE}
+                     COMMAND ${Python3_EXECUTABLE}
                              ${hctgen} ${force_lf}
                              ${mode} --output ${temp_output} ${input_flag}
                      ${format_cmd}

tools/clang/lib/Basic/CMakeLists.txt

@@ -102,7 +102,7 @@ if ( HLSL_SUPPORT_QUERY_GIT_COMMIT_INFO )
   set(GET_GIT_COMMIT_SCRIPT ${PROJECT_SOURCE_DIR}/utils/GetCommitInfo.py)
   add_custom_command(
     OUTPUT  ${GIT_COMMIT_INFO_FILE}
-    COMMAND ${PYTHON_EXECUTABLE} ${GET_GIT_COMMIT_SCRIPT}
+    COMMAND ${Python3_EXECUTABLE} ${GET_GIT_COMMIT_SCRIPT}
             ${PROJECT_SOURCE_DIR} ${GIT_COMMIT_INFO_FILE}
     DEPENDS ${GET_GIT_COMMIT_SCRIPT} GIT_COMMIT_INFO_ALWAYS_REBUILD
     COMMENT "Collect Git commit info for versioning"

utils/version/CMakeLists.txt

@@ -6,7 +6,7 @@ macro(generate_version_include name input_file output_file gen_flags)
         add_custom_command(
             OUTPUT ${gen_file}
             COMMAND echo Generating version
-            COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/gen_version.py ${gen_flags} > ${gen_file}
+	    COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/gen_version.py ${gen_flags} > ${gen_file}
             DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/gen_version.py
         )
     else ()