[Utils] Add a switch controlling prefix warnings in UpdateTestChecks

[mtrofin]

Summary

The switch controls both unused prefix warnings, and warnings about
functions which differ under different runs for a prefix, and, thus, end
up not having asserts for that prefix.

(If the latter case spans to all functions, then the former case kicks
in)

The switch is on by default, and can be disabled.

[jdoerfert]

this deserves a test I think

llvm/utils/UpdateTestChecks/common.py

274

leftover?

[mtrofin]

removed leftover

[mtrofin]

added test

[jdoerfert]

LG

[mtrofin]

added a test for disabling the switch, too

[RKSimon]

@mtrofin This is causing warning spam on lots of x86 test regenerations - are we sure its actually disabled by default like its supposed to be?

[mtrofin]

In D95829#2535179, @jdoerfert wrote:

this deserves a test I think

In D95829#2536222, @RKSimon wrote:

@mtrofin This is causing warning spam on lots of x86 test regenerations - are we sure its actually disabled by default like its supposed to be?

I'm not sure why it'd be supposed to be disabled by default. The old behavior (pre e2dc306b1ac71258e6ce40a66e778527f282c355) - while buggy - seemed to have the intention to warn frequently (but hard to tell, since it was buggy, see the description and discussion in https://reviews.llvm.org/D93078).

Separately, @craig.topper pointed at how his expectation was for this level of verbosity.

I would argue that the warnings have some value: they highlight functions that end up with no asserts under a prefix in a more compact way than visiting the generated file function by function - but happy to switch the default to whatever the broader community agrees to.

llvm/utils/UpdateTestChecks/common.py

274

yes - done.

[RKSimon]

This is still spewing out useless warnings - revert this?

[mtrofin]

This comment was removed by mtrofin.

[RKSimon]

Thanks!

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/common-label-different-bodies.test

 # REQUIRES: x86-registered-target
 
 # RUN: cp -f %S/Inputs/common-label-different-bodies-1.ll %t-1.ll
 # RUN: cp -f %S/Inputs/common-label-different-bodies-2.ll %t-2.ll
 # RUN: cp -f %S/Inputs/common-label-different-bodies-3.ll %t-3.ll
-# RUN: %update_llc_test_checks %t-1.ll
+# RUN: cp -f %S/Inputs/common-label-different-bodies-3.ll %t-4.ll
+# RUN: %update_llc_test_checks %t-1.ll 2>&1 | FileCheck %s --check-prefix=WARNINGS
+# RUN: %update_llc_test_checks --disable-verbose-prefix-warnings %t-4.ll 2>&1 | FileCheck %s --check-prefix=NOWARNINGS --allow-empty
 # RUN: %update_llc_test_checks %t-2.ll
 # RUN: %update_llc_test_checks %t-3.ll
 # RUN: FileCheck --input-file=%t-1.ll %s
 # RUN: FileCheck --input-file=%t-2.ll %s
 # RUN: FileCheck --input-file=%t-3.ll %s
 
 # CHECK: B-LABEL: fold_v2i64
-# CHECK-NOT: A-LABEL: fold_v2i64
+# CHECK-NOT: A-LABEL: fold_v2i64
+# WARNINGS: WARNING: Function fold_v2i64 had conflicting output from different RUN lines for prefix A
+# WARNINGS: WARNING: Prefix A had conflicting output from different RUN lines for all functions
+# NOWARNINGS-NOT: WARNING
 No newline at end of file

llvm/utils/UpdateTestChecks/common.py

def parse_commandline_args(parser):
   parser.add_argument('-u', '--update-only', action='store_true',
                       help='Only update test if it was already autogened')
   parser.add_argument('--force-update', action='store_true',
                       help='Update test even if it was autogened by a different script')
   parser.add_argument('--enable', action='store_true', dest='enabled', default=True,
                        help='Activate CHECK line generation from this point forward')
   parser.add_argument('--disable', action='store_false', dest='enabled',
                       help='Deactivate CHECK line generation from this point forward')
+  parser.add_argument('--disable-verbose-prefix-warnings', action='store_false', 
+                      default=True,
+                      dest='verbose_prefix_warnings',
+                      help='Disable warnings about unused prefixes.')
   args = parser.parse_args()
-  global _verbose
+  global _verbose, _verbose_prefix_warnings
   _verbose = args.verbose
+  _verbose_prefix_warnings = args.verbose_prefix_warnings
   return args
 
 
 class InputLineInfo(object):
   def __init__(self, line, line_number, args, argv):
     self.line = line
     self.line_number = line_number
     self.args = args

 class FunctionTestBuilder:
   def __init__(self, run_list, flags, scrubber_args):
     self._verbose = flags.verbose
     self._record_args = flags.function_signature
     self._check_attributes = flags.check_attributes
     self._scrubber_args = scrubber_args
     self._func_dict = {}
     self._func_order = {}
     for tuple in run_list:
       for prefix in tuple[0]:
         self._func_dict.update({prefix:dict()})
         self._func_order.update({prefix: []})
 
   def finish_and_get_func_dict(self):
+    if _verbose_prefix_warnings:
       for prefix in self._get_failed_prefixes():
         warn('Prefix %s had conflicting output from different RUN lines for all functions' % (prefix,))
     return self._func_dict
 
   def func_order(self):
     return self._func_order
   
   def process_run_line(self, function_re, scrubber, raw_tool_output, prefixes):
     for m in function_re.finditer(raw_tool_output):
       if not m:
for m in function_re.finditer(raw_tool_output):
               self._func_dict[prefix][func].args_and_sig = args_and_sig
               continue
             else:
               # This means a previous RUN line produced a body for this function
               # that is different from the one produced by this current RUN line,
               # so the body can't be common accross RUN lines. We use None to
               # indicate that.
               self._func_dict[prefix][func] = None
+              if _verbose_prefix_warnings:
+                warn('Function %s had conflicting output from different RUN lines for prefix %s' % (
+                    func, prefix))
               continue
 
         self._func_dict[prefix][func] = function_body(
             scrubbed_body, scrubbed_extra, args_and_sig, attrs)
         self._func_order[prefix].append(func)
 
   def _get_failed_prefixes(self):
     # This returns the list of those prefixes that failed to match any function,