Index: utils/update_cc_test_checks.py
===================================================================
--- /dev/null
+++ utils/update_cc_test_checks.py
@@ -0,0 +1,212 @@
+#!/usr/bin/env python3
+'''A utility to update LLVM IR or assembly CHECK lines in C/C++ FileCheck test files.
+
+Example RUN lines in .c/.cc test files:
+
+// RUN: %clang -S %s -o - -O2 | FileCheck %s
+// RUN: %clang -emit-llvm -S %s -o - -O2 | FileCheck %s
+
+Usage:
+
+% utils/update_cc_test_checks.py --llvm-bin=release/bin test/a.cc
+% utils/update_cc_test_checks.py --c-index-test=release/bin/c-index-test \
+  --clang=release/bin/clang /tmp/c/a.cc
+'''
+
+import argparse
+import distutils.spawn
+import os         # Used to advertise this file's name ("autogenerated_note").
+import shlex
+import string
+import subprocess
+import sys
+import re
+import tempfile
+
+from UpdateTestChecks import asm, common
+
+ADVERT = '// NOTE: Assertions have been autogenerated by '
+
+CHECK_RE = re.compile(r'^\s*//\s*([^:]+?)(?:-NEXT|-NOT|-DAG|-LABEL)?:')
+RUN_LINE_RE = re.compile('^//\s*RUN:\s*(.*)$')
+
+def get_line2spell_and_mangled(args, filename, clang_args):
+  ret = {}
+  with tempfile.NamedTemporaryFile() as f:
+    # TODO Make c-index-test print mangled names without circumventing through precompiled headers
+    subprocess.check_call([args.c_index_test,
+        '-write-pch', f.name, filename, *shlex.split(clang_args), *args.c_index_test_args])
+    output = subprocess.check_output([args.c_index_test,
+        '-test-print-mangle', f.name])
+    if sys.version_info[0] > 2:
+      output = output.decode()
+
+  RE = re.compile(r'^FunctionDecl=(\w+):(\d+):\d+ \(Definition\) \[mangled=([^]]+)\]')
+  for line in output.splitlines():
+    m = RE.match(line)
+    if not m: continue
+    spell, line, mangled = m.groups()
+    ret[int(line)-1] = (spell, mangled)
+  if args.verbose:
+    for line, func_name in ret.items():
+      print('line {}: found function {}'.format(line+1, func_name), file=sys.stderr)
+  return ret
+
+
+def main():
+  parser = argparse.ArgumentParser(
+      description=__doc__,
+      formatter_class=argparse.RawTextHelpFormatter)
+  parser.add_argument('-v', '--verbose', action='store_true')
+  parser.add_argument('--llvm-bin', help='llvm $prefix/bin path')
+  parser.add_argument('--clang',
+                      help='"clang" executable, defaults to $llvm_bin/clang')
+  parser.add_argument('--clang-args',
+                      help='Space-separated extra args to clang')
+  parser.add_argument('--c-index-test',
+                      help='"c-index-test" executable, defaults to $llvm_bin/c-index-test')
+  parser.add_argument('--c-index-test-args',
+                      help='Space-separated extra args to c-index-test, e.g. -resource-dir clang/7.0.0')
+  parser.add_argument(
+      '--functions', nargs='+', help='A list of function name regexes. '
+      'If specified, update CHECK lines for functions matching at least one regex')
+  parser.add_argument(
+      '--x86_extra_scrub', action='store_true',
+      help='Use more regex for x86 matching to reduce diffs between various subtargets')
+  parser.add_argument('tests', nargs='+')
+  args = parser.parse_args()
+  args.c_index_test_args = shlex.split(args.c_index_test_args or '')
+
+  if args.clang is None:
+    if args.llvm_bin is None:
+      args.clang = 'clang'
+    else:
+      args.clang = os.path.join(args.llvm_bin, 'clang')
+  if not distutils.spawn.find_executable(args.clang):
+    print('Please specify --llvm-bin or --clang-exe', file=sys.stderr)
+    return 1
+  if args.c_index_test is None:
+    if args.llvm_bin is None:
+      args.c_index_test = 'c-index-test'
+    else:
+      args.c_index_test = os.path.join(args.llvm_bin, 'c-index-test')
+  if not distutils.spawn.find_executable(args.c_index_test):
+    print('Please specify --llvm-bin or --c-index-test-exe', file=sys.stderr)
+    return 1
+
+  autogenerated_note = (ADVERT + 'utils/' + os.path.basename(__file__))
+
+  for filename in args.tests:
+    with open(filename) as f:
+      input_lines = [l.rstrip() for l in f]
+
+    # Parse RUN lines and get `prefix_set`.
+    raw_lines = [m.group(1)
+                 for m in [RUN_LINE_RE.match(l) for l in input_lines] if m]
+    run_lines = [raw_lines[0]] if len(raw_lines) > 0 else []
+    for l in raw_lines[1:]:
+      if run_lines[-1].endswith("\\"):
+        run_lines[-1] = run_lines[-1].rstrip("\\") + " " + l
+      else:
+        run_lines.append(l)
+
+    if args.verbose:
+      print('Found {} RUN lines:'.format(len(run_lines)), file=sys.stderr)
+      for l in run_lines:
+        print('  RUN: ' + l, file=sys.stderr)
+
+    # Build a list of clang command lines from RUN lines.
+    run_list = []
+    line2spell_and_mangled = {}
+    for l in run_lines:
+      commands = [cmd.strip() for cmd in l.split('|', 1)]
+      clang_cmd = commands[0]
+
+      triple_in_cmd = None
+      m = common.TRIPLE_ARG_RE.search(clang_cmd)
+      if m:
+        triple_in_cmd = m.groups()[0]
+
+      filecheck_cmd = commands[-1]
+      if clang_cmd.startswith('%clang '):
+        clang_args = clang_cmd[len('%clang '):].strip()
+      elif clang_cmd.startswith('%clang_cc1 '):
+        clang_args = clang_cmd.replace('%clang_cc1 ', '-cc1 ').strip()
+      else:
+        print('WARNING: Skipping non-clang RUN line: ' + l, file=sys.stderr)
+        continue
+
+      if not filecheck_cmd.startswith('FileCheck '):
+        print('WARNING: Skipping non-FileChecked RUN line: ' + l, file=sys.stderr)
+        continue
+
+      # Invoke c-index-test to get mapping from start lines to mangled names.
+      # Forward all clang args for now.
+      line2spell_and_mangled.update(get_line2spell_and_mangled(args, filename, clang_args))
+
+      check_prefixes = [item for m in common.CHECK_PREFIX_RE.finditer(filecheck_cmd)
+                               for item in m.group(1).split(',')]
+      if not check_prefixes:
+        check_prefixes = ['CHECK']
+      run_list.append((check_prefixes, clang_args.replace('%s', filename), triple_in_cmd))
+
+    # Execute clang, generate assembly, and extract functions.
+    func_dict = {}
+    for p in run_list:
+      prefixes = p[0]
+      for prefix in prefixes:
+        func_dict.update({prefix: dict()})
+    for prefixes, clang_args, triple_in_cmd in run_list:
+      if args.verbose:
+        print('Extracted clang cmd: clang {}'.format(clang_args), file=sys.stderr)
+        print('Extracted FileCheck prefixes: {}'.format(prefixes), file=sys.stderr)
+
+      if args.clang_args:
+        clang_args += ' ' + args.clang_args
+      raw_tool_output = common.invoke_tool(args.clang,
+                                           clang_args,
+                                           filename)
+
+      if '-emit-llvm' in clang_args:
+        common.build_function_body_dictionary(
+                common.OPT_FUNCTION_RE, common.scrub_body, [],
+                raw_tool_output, prefixes, func_dict, args.verbose)
+      else:
+        asm.build_function_body_dictionary_for_triple(args, raw_tool_output,
+            triple_in_cmd or 'x86', prefixes, func_dict)
+
+    # Strip CHECK lines which are in `prefix_set`, update test file.
+    prefix_set = set([prefix for p in run_list for prefix in p[0]])
+    input_lines = []
+    with open(filename, 'r+') as f:
+      for line in f:
+        m = CHECK_RE.match(line)
+        if not (m and m.group(1) in prefix_set) and line != '//\n':
+          input_lines.append(line)
+      f.seek(0)
+      f.writelines(input_lines)
+      f.truncate()
+
+    output_lines = [autogenerated_note]
+    for idx, line in enumerate(input_lines):
+      # Discard any previous script advertising.
+      if line.startswith(ADVERT):
+        continue
+      if idx in line2spell_and_mangled:
+        spell, mangled = line2spell_and_mangled[idx]
+        # If --functions is unspecified or one regex matches the spelling name.
+        if args.functions is None or any(re.search(regex, spell)
+                                         for regex in args.functions):
+          asm.add_asm_checks(output_lines, '//', run_list, func_dict, mangled)
+      output_lines.append(line.rstrip('\n'))
+
+    # Update the test file.
+    with open(filename, 'w') as f:
+      for line in output_lines:
+        f.write(line + '\n')
+
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())