build_script: Add an option to build the swift libraries multiple times to check if incremental compilation works.

A script checks if the output object file is written only once even if the compiler is invoked multiple times.
The main purpose of this check is to ensure that the compiler is deterministic (until IRGen).

Author: eeckstein

CMakeLists.txt

@@ -36,6 +36,10 @@ option(SWIFT_STDLIB_SIL_DEBUGGING
     "Compile the Swift standard library with -gsil to enable debugging and profiling on SIL level"
     FALSE)
 
+option(SWIFT_CHECK_INCREMENTAL_COMPILATION
+    "Check if incremental compilation works when compiling the Swift libraries"
+    FALSE)
+
 option(SWIFT_BUILD_TOOLS
     "Build the Swift compiler and other tools"
     TRUE)

cmake/modules/SwiftSource.cmake

@@ -369,6 +369,10 @@ function(_compile_swift_files dependency_target_out_var_name)
     set(main_command "-emit-sib")
   endif()
 
+  if (SWIFT_CHECK_INCREMENTAL_COMPILATION)
+    set(swift_compiler_tool "${SWIFT_SOURCE_DIR}/utils/check-incremental" "${swift_compiler_tool}")
+  endif()
+
   add_custom_command_target(
       dependency_target
       ${command_create_dirs}

utils/build-script-impl

@@ -166,6 +166,7 @@ KNOWN_SETTINGS=(
     build-swift-examples        "1"              "set to 1 to build examples"
     build-serialized-stdlib-unittest "0"         "set to 1 to build the StdlibUnittest module with -sil-serialize-all"
     build-sil-debugging-stdlib  "0"              "set to 1 to build the Swift standard library with -gsil to enable debugging and profiling on SIL level"
+    check-incremental-compilation "0"            "set to 1 to compile swift libraries multiple times to check if incremental compilation works"
     source-tree-includes-tests  "1"              "set to 0 to allow the build to proceed when 'test' directory is missing (required for B&I builds)"
     native-llvm-tools-path      ""               "directory that contains LLVM tools that are executable on the build machine"
     native-clang-tools-path     ""               "directory that contains Clang tools that are executable on the build machine"
@@ -1645,6 +1646,7 @@ for deployment_target in "${HOST_TARGET}" "${CROSS_COMPILE_TOOLS_DEPLOYMENT_TARG
                     -DSWIFT_BUILD_STDLIB:BOOL=$(true_false "${BUILD_SWIFT_STDLIB}")
                     -DSWIFT_SERIALIZE_STDLIB_UNITTEST:BOOL=$(true_false "${BUILD_SERIALIZED_STDLIB_UNITTEST}")
                     -DSWIFT_STDLIB_SIL_DEBUGGING:BOOL=$(true_false "${BUILD_SIL_DEBUGGING_STDLIB}")
+                    -DSWIFT_CHECK_INCREMENTAL_COMPILATION:BOOL=$(true_false "${CHECK_INCREMENTAL_COMPILATION}")
                     -DSWIFT_BUILD_SDK_OVERLAY:BOOL=$(true_false "${BUILD_SWIFT_SDK_OVERLAY}")
                     -DSWIFT_BUILD_STATIC_STDLIB:BOOL=$(true_false "${BUILD_SWIFT_STATIC_STDLIB}")
                     -DSWIFT_BUILD_PERF_TESTSUITE:BOOL=$(true_false "${build_perf_testsuite_this_time}")

utils/check-incremental

@@ -0,0 +1,92 @@
+#!/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 - 2016 Apple Inc. and the Swift project authors
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See http://swift.org/LICENSE.txt for license information
+# See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+#
+# ----------------------------------------------------------------------------
+#
+# This is a wrapper for the swift compiler.
+# It invokes the compiler multiple times and checks if the output object file
+# is only written a single time.
+# The main purpose of the check is to ensure that the compiler is
+# deterministic.
+#
+# ----------------------------------------------------------------------------
+
+import subprocess
+import os
+import sys
+import time
+
+
+def main():
+  verbose = False
+  num_iterations = 4
+
+  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
+
+  if not write_obj_file or output_file is None:
+    return
+
+  new_args = sys.argv[1:]
+  subprocess.check_call(new_args)
+
+  if verbose:
+    print "Reference compilation of " + output_file + ":"
+
+  reference_md5 = subprocess.check_output(["md5", "-q", output_file])
+  reference_time = os.path.getmtime(output_file)
+
+  if verbose:
+    print "  time = {}".format(reference_time)
+    print "  md5 = " + reference_md5
+
+  subprocess.check_call(["cp", output_file, output_file + ".ref.o"])
+
+  for iteration in range(0, num_iterations):
+
+    if verbose:
+      print "Iteration {}:".format(iteration)
+
+    subprocess.check_call(new_args)
+
+    second_md5 = subprocess.check_output(["md5", "-q", output_file])
+    second_time = os.path.getmtime(output_file)
+
+    if verbose:
+      print "  time = {}".format(second_time)
+      print "  md5 = " + second_md5
+
+    # 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)
+
+    # 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)
+
+
+main()
+