Revert "build: use find_package(Python3) if available"

This reverts commit cd84bfb8142bc7ff3a07a188ffb809f1d86d1fd7.  Although
this passed the CI in phabricator, some of the bots are missing python3
packages, revert it temporarily.

CMakeLists.txt

@@ -672,38 +672,16 @@ option(LLVM_ENABLE_PLUGINS "Enable plugin support" ${LLVM_ENABLE_PLUGINS_default
 
 include(HandleLLVMOptions)
 
-if(CMAKE_VERSION VERSION_LESS 3.12)
-  include(FindPythonInterp)
-  if( NOT PYTHONINTERP_FOUND )
-    message(FATAL_ERROR
-  "Unable to find Python interpreter, required for builds and testing.
+include(FindPythonInterp)
+if( NOT PYTHONINTERP_FOUND )
+  message(FATAL_ERROR
+"Unable to find Python interpreter, required for builds and testing.
 
-  Please install Python or specify the PYTHON_EXECUTABLE CMake variable.")
-  endif()
+Please install Python or specify the PYTHON_EXECUTABLE CMake variable.")
+endif()
 
-  if( ${PYTHON_VERSION_STRING} VERSION_LESS 2.7 )
-    message(FATAL_ERROR "Python 2.7 or newer is required")
-  endif()
-
-  add_executable(Python3::Interpreter IMPORTED)
-  set_target_properties(Python3::Interpreter PROPERTIES
-    IMPORTED_LOCATION ${PYTHON_EXECUTABLE})
-  set(Python3_EXECUTABLE ${PYTHON_EXECUTABLE})
-else()
-  find_package(Python3 COMPONENTS Interpreter)
-  if(NOT Python3_Interpreter_FOUND)
-    message(WARNING "Python3 not found, using python2 as a fallback")
-    find_package(Python2 COMPONENTS Interpreter REQUIRED)
-    if(Python2_VERSION VERSION_LESS 2.7)
-      message(SEND_ERROR "Python 2.7 or newer is required")
-    endif()
-
-    # Treat python2 as python3
-    add_executable(Python3::Interpreter IMPORTED)
-    set_target_properties(Python3::Interpreter PROPERTIES
-      IMPORTED_LOCATION ${Python2_EXECUTABLE})
-    set(Python3_EXECUTABLE ${Python2_EXECUTABLE})
-  endif()
+if( ${PYTHON_VERSION_STRING} VERSION_LESS 2.7 )
+  message(FATAL_ERROR "Python 2.7 or newer is required")
 endif()
 
 ######
@@ -739,7 +717,7 @@ endif (LLVM_USE_PERF)
 
 message(STATUS "Constructing LLVMBuild project information")
 execute_process(
-  COMMAND "${Python3_EXECUTABLE}" -B ${LLVMBUILDTOOL}
+  COMMAND ${PYTHON_EXECUTABLE} -B ${LLVMBUILDTOOL}
             --native-target "${LLVM_NATIVE_ARCH}"
             --enable-targets "${LLVM_TARGETS_TO_BUILD}"
             --enable-optional-components "${LLVMOPTIONALCOMPONENTS}"

cmake/config-ix.cmake

@@ -639,7 +639,7 @@ function(find_python_module module)
     return()
   endif()
 
-  execute_process(COMMAND "${Python3_EXECUTABLE}" "-c" "import ${module}"
+  execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c" "import ${module}"
     RESULT_VARIABLE status
     ERROR_QUIET)
 

cmake/modules/AddLLVM.cmake

@@ -117,7 +117,7 @@ function(add_llvm_symbol_exports target_name export_file)
     set(native_export_file "${target_name}.def")
 
     add_custom_command(OUTPUT ${native_export_file}
-      COMMAND "${Python3_EXECUTABLE}" -c "import sys;print(''.join(['EXPORTS\\n']+sys.stdin.readlines(),))"
+      COMMAND ${PYTHON_EXECUTABLE} -c "import sys;print(''.join(['EXPORTS\\n']+sys.stdin.readlines(),))"
         < ${export_file} > ${native_export_file}
       DEPENDS ${export_file}
       VERBATIM
@@ -1046,7 +1046,7 @@ function(export_executable_symbols target)
       set(mangling itanium)
     endif()
     add_custom_command(OUTPUT ${exported_symbol_file}
-                       COMMAND "${Python3_EXECUTABLE}" ${LLVM_MAIN_SRC_DIR}/utils/extract_symbols.py --mangling=${mangling} ${static_libs} -o ${exported_symbol_file}
+                       COMMAND ${PYTHON_EXECUTABLE} ${LLVM_MAIN_SRC_DIR}/utils/extract_symbols.py --mangling=${mangling} ${static_libs} -o ${exported_symbol_file}
                        WORKING_DIRECTORY ${LLVM_LIBRARY_OUTPUT_INTDIR}
                        DEPENDS ${LLVM_MAIN_SRC_DIR}/utils/extract_symbols.py ${static_libs}
                        VERBATIM
@@ -1447,7 +1447,7 @@ function(make_paths_relative out_pathlist basedir pathlist)
   # empty list entries. So escape the ;s in the list and do the splitting
   # ourselves. cmake has no relpath function, so use Python for that.
   string(REPLACE ";" "\\;" pathlist_escaped "${pathlist}")
-  execute_process(COMMAND "${Python3_EXECUTABLE}" "-c" "\n
+  execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c" "\n
 import os, sys\n
 base = sys.argv[1]
 def haslink(p):\n
@@ -1522,6 +1522,7 @@ function(configure_lit_site_cfg site_in site_out)
   # 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)
@@ -1679,7 +1680,7 @@ function(add_lit_target target comment)
     ALLOW_EXTERNAL
     )
 
-  set(LIT_COMMAND "${Python3_EXECUTABLE};${lit_base_dir}/${lit_file_name}")
+  set(LIT_COMMAND "${PYTHON_EXECUTABLE};${lit_base_dir}/${lit_file_name}")
   list(APPEND LIT_COMMAND ${LIT_ARGS})
   foreach(param ${ARG_PARAMS})
     list(APPEND LIT_COMMAND --param ${param})

test/lit.site.cfg.py.in

@@ -12,7 +12,7 @@ config.llvm_shlib_dir = path(r"@SHLIBDIR@")
 config.llvm_shlib_ext = "@SHLIBEXT@"
 config.llvm_exe_ext = "@EXEEXT@"
 config.lit_tools_dir = path(r"@LLVM_LIT_TOOLS_DIR@")
-config.python_executable = "@Python3_EXECUTABLE@"
+config.python_executable = "@PYTHON_EXECUTABLE@"
 config.gold_executable = "@GOLD_EXECUTABLE@"
 config.ld64_executable = "@LD64_EXECUTABLE@"
 config.ocamlfind_executable = "@OCAMLFIND@"

tools/llvm-shlib/CMakeLists.txt

@@ -164,7 +164,7 @@ if(LLVM_BUILD_LLVM_C_DYLIB AND MSVC)
   endif()
 
   add_custom_command(OUTPUT ${LLVM_EXPORTED_SYMBOL_FILE}
-    COMMAND "${Python3_EXECUTABLE}" ${GEN_SCRIPT} --libsfile ${LIBSFILE} ${GEN_UNDERSCORE} --nm "${llvm_nm}" -o ${LLVM_EXPORTED_SYMBOL_FILE}
+    COMMAND ${PYTHON_EXECUTABLE} ${GEN_SCRIPT} --libsfile ${LIBSFILE} ${GEN_UNDERSCORE} --nm "${llvm_nm}" -o ${LLVM_EXPORTED_SYMBOL_FILE}
     DEPENDS ${LIB_NAMES} ${llvm_nm_target}
     COMMENT "Generating export list for LLVM-C"
     VERBATIM )