Index: llvm/utils/UpdateTestChecks/common.py
===================================================================
--- llvm/utils/UpdateTestChecks/common.py
+++ llvm/utils/UpdateTestChecks/common.py
@@ -323,6 +323,9 @@
             with open(test) as f:
                 input_lines = [l.rstrip() for l in f]
             first_line = input_lines[0] if input_lines else ""
+            if UTC_AVOID in first_line:
+              warn("Skipping test that must not be autogenerated: " + test)
+              continue
             is_regenerate = UTC_ADVERT in first_line
 
             # If we're generating a new test, set the default version to the latest.
@@ -464,6 +467,7 @@
 UTC_ARGS_KEY = "UTC_ARGS:"
 UTC_ARGS_CMD = re.compile(r".*" + UTC_ARGS_KEY + "\s*(?P<cmd>.*)\s*$")
 UTC_ADVERT = "NOTE: Assertions have been autogenerated by "
+UTC_AVOID = "NOTE: Do not autogenerate "
 UNUSED_NOTE = "NOTE: These prefixes are unused and the list is autogenerated. Do not add tests below this line:"
 
 OPT_FUNCTION_RE = re.compile(