utils/check-incremental

#!/usr/bin/env python
# check-incremental - Check if incremental compilation works -*- python -*-
#
# This source file is part of the Swift.org open source project
#
# Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
# Licensed under Apache License v2.0 with Runtime Library Exception
#
# See https://swift.org/LICENSE.txt for license information
# See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
#
"""
check-incremental: Check if incremental compilation works.

This is a wrapper for the Swift compiler.  It invokes the compiler
multiple times and checks if the output object file is only written once.
The main purpose of the check is to ensure that the compiler is
deterministic.
"""

from __future__ import print_function

import os
import subprocess
import sys
import time


VERBOSE = False
NUM_ITERATIONS = 4


def compile_and_stat(compile_args, output_file):
    """Perform a compilation using ``compile_args``, and return a tuple
    (md5sum, last modified time) for ``output_file`` after the
    compilation has finished.
    """
    subprocess.check_call(compile_args)

    md5 = subprocess.check_output(["md5", "-q", output_file])
    mtime = time.ctime(os.path.getmtime(output_file))

    if VERBOSE:
        print(" time = " + str(mtime))
        print("  md5 = " + md5)

    return (md5, mtime)


def main():

    write_obj_file = False
    next_arg_is_output = False
    compare_time = True
    output_file = None

    for arg in sys.argv:
        if next_arg_is_output:
            output_file = arg
            next_arg_is_output = False
        elif arg == '-c':
            write_obj_file = True
        elif arg == '-disable-incremental-llvm-codegen':
            compare_time = False
        elif arg == '-o':
            next_arg_is_output = True

    new_args = sys.argv[1:]

    if not write_obj_file or output_file is None:
        subprocess.check_call(new_args)
        return

    if VERBOSE:
        print("Reference compilation of " + output_file + ":")

    # As a workaround for rdar://problem/43442957 and rdar://problem/43439465
    # we have to "warm-up" the clang module cache. Without that in some cases
    # we end up with small differences in the debug info.
    compile_and_stat(new_args, output_file)

    reference_md5, reference_time = compile_and_stat(new_args, output_file)

    subprocess.check_call(["cp", output_file, output_file + ".ref.o"])

    for iteration in range(1, NUM_ITERATIONS + 1):

        if VERBOSE:
            print("Iteration {}:".format(iteration))

        second_md5, second_time = compile_and_stat(new_args, output_file)

        # This is the most important check: is the output file exactly the
        # same.
        if reference_md5 != second_md5:
            sys.exit("non-determinism when generating: " + output_file +
                     "\ncommand line:\n" + " ".join(new_args))

        # This is the bonus check: does the compiler not re-write the output
        # file. (For compilations < 1sec this check may succeed even if the
        # file was overwritten).
        if compare_time and reference_time != second_time:
            sys.exit("file re-written: " + output_file)


if __name__ == '__main__':
    main()