diff --git a/llvm/utils/UpdateTestChecks/common.py b/llvm/utils/UpdateTestChecks/common.py
--- a/llvm/utils/UpdateTestChecks/common.py
+++ b/llvm/utils/UpdateTestChecks/common.py
@@ -2,6 +2,7 @@
 
 import copy
 import glob
+import os
 import re
 import subprocess
 import sys
@@ -127,11 +128,23 @@
   return True
 
 # Invoke the tool that is being tested.
-def invoke_tool(exe, cmd_args, ir):
+def invoke_tool(exe, cmd_args, ir, preprocess_cmd=None, verbose=False):
   with open(ir) as ir_file:
     # TODO Remove the str form which is used by update_test_checks.py and
     # update_llc_test_checks.py
     # The safer list form is used by update_cc_test_checks.py
+    if preprocess_cmd:
+      # Allow pre-processing the IR file (e.g. using sed):
+      assert isinstance(preprocess_cmd, str)  # TODO: use a list instead of using shell
+      preprocess_cmd = preprocess_cmd.replace('%s', ir).strip()
+      if verbose:
+        print('Pre-processing ir_file: ', ir, " with command '",
+              preprocess_cmd, "'", sep="", file=sys.stderr)
+      # Python 2.7 doesn't have subprocess.DEVNULL:
+      with open(os.devnull, 'w') as devnull:
+        pp = subprocess.Popen(preprocess_cmd, shell=True, stdin=devnull,
+                              stdout=subprocess.PIPE)
+        ir_file = pp.stdout
     if isinstance(cmd_args, list):
       stdout = subprocess.check_output([exe] + cmd_args, stdin=ir_file)
     else:
diff --git a/llvm/utils/update_test_checks.py b/llvm/utils/update_test_checks.py
--- a/llvm/utils/update_test_checks.py
+++ b/llvm/utils/update_test_checks.py
@@ -78,7 +78,13 @@
         common.warn('Skipping unparseable RUN line: ' + l)
         continue
 
-      (tool_cmd, filecheck_cmd) = tuple([cmd.strip() for cmd in l.split('|', 1)])
+      commands = [cmd.strip() for cmd in l.split('|')]
+      assert len(commands) >= 2
+      preprocess_cmd = None
+      if len(commands) > 2:
+        preprocess_cmd = " | ".join(commands[:-2])
+      tool_cmd = commands[-2]
+      filecheck_cmd = commands[-1]
       common.verify_filecheck_prefixes(filecheck_cmd)
       if not tool_cmd.startswith(opt_basename + ' '):
         common.warn('Skipping non-%s RUN line: %s' % (opt_basename, l))
@@ -99,7 +105,7 @@
 
       # FIXME: We should use multiple check prefixes to common check lines. For
       # now, we just ignore all but the last.
-      prefix_list.append((check_prefixes, tool_cmd_args))
+      prefix_list.append((check_prefixes, tool_cmd_args, preprocess_cmd))
 
     global_vars_seen_dict = {}
     builder = common.FunctionTestBuilder(
@@ -107,19 +113,20 @@
       flags=ti.args,
       scrubber_args=[])
 
-    for prefixes, opt_args in prefix_list:
+    for prefixes, opt_args, preprocess_cmd in prefix_list:
       common.debug('Extracted opt cmd: ' + opt_basename + ' ' + opt_args)
       common.debug('Extracted FileCheck prefixes: ' + str(prefixes))
 
-      raw_tool_output = common.invoke_tool(ti.args.opt_binary, opt_args, 
-                                           ti.path)
+      raw_tool_output = common.invoke_tool(ti.args.opt_binary, opt_args,
+                                           ti.path, preprocess_cmd=preprocess_cmd,
+                                           verbose=ti.args.verbose)
       builder.process_run_line(common.OPT_FUNCTION_RE, common.scrub_body,
               raw_tool_output, prefixes)
 
     func_dict = builder.finish_and_get_func_dict()
     is_in_function = False
     is_in_function_start = False
-    prefix_set = set([prefix for prefixes, _ in prefix_list for prefix in prefixes])
+    prefix_set = set([prefix for prefixes, _, _ in prefix_list for prefix in prefixes])
     common.debug('Rewriting FileCheck prefixes:', str(prefix_set))
     output_lines = []