build: use `find_package(Python3)` if available

This is primarily motivated by the desire to move from Python2 to
Python3.  `PYTHON_EXECUTABLE` is ambiguous.  This explicitly identifies
the python interpreter in use.  Since the LLVM build seems to be able to
completed successfully with python3, use that across the build.  The old
path aliases `PYTHON_EXECUTABLE` to be treated as Python3.

6 files changed, 38 insertions, 16 deletions

diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index 88e556f..7dadc5f 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -130,16 +130,38 @@ if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
   set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
 
   if(LLVM_INCLUDE_TESTS)
-    include(FindPythonInterp)
-    if(NOT PYTHONINTERP_FOUND)
-      message(FATAL_ERROR
-"Unable to find Python interpreter, required for builds and testing.
+    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.
 
-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()
 
-    if( ${PYTHON_VERSION_STRING} VERSION_LESS 2.7 )
-      message(FATAL_ERROR "Python 2.7 or newer is required")
+      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()
     endif()
 
     # Check prebuilt llvm/utils.
diff --git a/clang/bindings/python/tests/CMakeLists.txt b/clang/bindings/python/tests/CMakeLists.txt
index 626256a..3f58c4b 100644
--- a/clang/bindings/python/tests/CMakeLists.txt
+++ b/clang/bindings/python/tests/CMakeLists.txt
@@ -3,7 +3,7 @@
 add_custom_target(check-clang-python
     COMMAND ${CMAKE_COMMAND} -E env
             CLANG_LIBRARY_PATH=$<TARGET_FILE_DIR:libclang>
-            ${PYTHON_EXECUTABLE} -m unittest discover
+            "${Python3_EXECUTABLE}" -m unittest discover
     DEPENDS libclang
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/..)
 
diff --git a/clang/test/lit.site.cfg.py.in b/clang/test/lit.site.cfg.py.in
index daec694..4527cca 100644
--- a/clang/test/lit.site.cfg.py.in
+++ b/clang/test/lit.site.cfg.py.in
@@ -27,7 +27,7 @@ config.enable_backtrace = @ENABLE_BACKTRACES@
 config.enable_experimental_new_pass_manager = @ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER@
 config.enable_threads = @LLVM_ENABLE_THREADS@
 config.host_arch = "@HOST_ARCH@"
-config.python_executable = "@PYTHON_EXECUTABLE@"
+config.python_executable = "@Python3_EXECUTABLE@"
 config.use_z3_solver = lit_config.params.get('USE_Z3_SOLVER', "@USE_Z3_SOLVER@")
 config.has_plugins = @LLVM_ENABLE_PLUGINS@
 
diff --git a/clang/utils/perf-training/CMakeLists.txt b/clang/utils/perf-training/CMakeLists.txt
index 1f86122..172076f 100644
--- a/clang/utils/perf-training/CMakeLists.txt
+++ b/clang/utils/perf-training/CMakeLists.txt
@@ -23,7 +23,7 @@ if(LLVM_BUILD_INSTRUMENTED)
     )
 
   add_custom_target(clear-profraw
-    COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py clean ${CMAKE_CURRENT_BINARY_DIR} profraw
+    COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py clean ${CMAKE_CURRENT_BINARY_DIR} profraw
     COMMENT "Clearing old profraw data")
 
   if(NOT LLVM_PROFDATA)
@@ -34,7 +34,7 @@ if(LLVM_BUILD_INSTRUMENTED)
     message(STATUS "To enable merging PGO data LLVM_PROFDATA has to point to llvm-profdata")
   else()
     add_custom_target(generate-profdata
-      COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py merge ${LLVM_PROFDATA} ${CMAKE_CURRENT_BINARY_DIR}/clang.profdata ${CMAKE_CURRENT_BINARY_DIR}
+      COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py merge ${LLVM_PROFDATA} ${CMAKE_CURRENT_BINARY_DIR}/clang.profdata ${CMAKE_CURRENT_BINARY_DIR}
       COMMENT "Merging profdata"
       DEPENDS generate-profraw)
   endif()
@@ -55,7 +55,7 @@ if(APPLE AND DTRACE)
     )
 
   add_custom_target(clear-dtrace-logs
-    COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py clean ${CMAKE_CURRENT_BINARY_DIR} dtrace
+    COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py clean ${CMAKE_CURRENT_BINARY_DIR} dtrace
     COMMENT "Clearing old dtrace data")
 
   if(NOT CLANG_ORDER_FILE)
@@ -63,7 +63,7 @@ if(APPLE AND DTRACE)
   endif()
 
   add_custom_target(generate-order-file
-    COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py gen-order-file --binary $<TARGET_FILE:clang> --output ${CLANG_ORDER_FILE} ${CMAKE_CURRENT_BINARY_DIR}
+    COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py gen-order-file --binary $<TARGET_FILE:clang> --output ${CLANG_ORDER_FILE} ${CMAKE_CURRENT_BINARY_DIR}
     COMMENT "Generating order file"
     DEPENDS generate-dtrace-logs)
 endif()
diff --git a/clang/utils/perf-training/lit.site.cfg.in b/clang/utils/perf-training/lit.site.cfg.in
index 340a0e9..a1c6d6b 100644
--- a/clang/utils/perf-training/lit.site.cfg.in
+++ b/clang/utils/perf-training/lit.site.cfg.in
@@ -7,7 +7,7 @@ config.perf_helper_dir = "@CMAKE_CURRENT_SOURCE_DIR@"
 config.test_exec_root = "@CMAKE_CURRENT_BINARY_DIR@"
 config.test_source_root = "@CLANG_PGO_TRAINING_DATA@"
 config.target_triple = "@TARGET_TRIPLE@"
-config.python_exe = "@PYTHON_EXECUTABLE@"
+config.python_exe = "@Python3_EXECUTABLE@"
 
 # Support substitution of the tools and libs dirs with user parameters. This is
 # used when we can't determine the tool dir at configuration time.
diff --git a/clang/utils/perf-training/order-files.lit.site.cfg.in b/clang/utils/perf-training/order-files.lit.site.cfg.in
index 87406db..91f2b79 100644
--- a/clang/utils/perf-training/order-files.lit.site.cfg.in
+++ b/clang/utils/perf-training/order-files.lit.site.cfg.in
@@ -7,7 +7,7 @@ config.perf_helper_dir = "@CMAKE_CURRENT_SOURCE_DIR@"
 config.test_exec_root = "@CMAKE_CURRENT_BINARY_DIR@"
 config.test_source_root = "@CLANG_PGO_TRAINING_DATA@"
 config.target_triple = "@TARGET_TRIPLE@"
-config.python_exe = "@PYTHON_EXECUTABLE@"
+config.python_exe = "@Python3_EXECUTABLE@"
 
 # Support substitution of the tools and libs dirs with user parameters. This is
 # used when we can't determine the tool dir at configuration time.