[UpdateTestChecks] Drop and update test checks

[xbolva00]

Summary

Motivation: Regeneration of correct test actually breaks it.

Example:

define i32 @test1(i64 %x) nounwind readnone {
  %count = tail call i64 @llvm.ctpop.i64(i64 %x)
  %cast = trunc i64 %count to i32
  %cmp = icmp ugt i32 %cast, 1
  %conv = zext i1 %cmp to i32
  ret i32 %conv
}

; CHECK-LABEL: test1:
; CHECK:       # %bb.0:
; CHECK-NEXT:    leaq -1(%rdi), %rcx
; CHECK-NEXT:    xorl %eax, %eax
; CHECK-NEXT:    testq %rcx, %rdi
; CHECK-NEXT:    setne %al
; CHECK-NEXT:    retq

-> PASS

Script updates it:
define i32 @test1(i64 %x) nounwind readnone {
; CHECK-LABEL: test1:
; CHECK:       # %bb.0:
; CHECK-NEXT:    leaq -1(%rdi), %rcx
; CHECK-NEXT:    xorl %eax, %eax
; CHECK-NEXT:    testq %rcx, %rdi
; CHECK-NEXT:    setne %al
; CHECK-NEXT:    retq
  %count = tail call i64 @llvm.ctpop.i64(i64 %x)
  %cast = trunc i64 %count to i32
  %cmp = icmp ugt i32 %cast, 1
  %conv = zext i1 %cmp to i32
  ret i32 %conv
}

; CHECK-LABEL: test1:
; CHECK:       # %bb.0:
; CHECK-NEXT:    leaq -1(%rdi), %rcx
; CHECK-NEXT:    xorl %eax, %eax
; CHECK-NEXT:    testq %rcx, %rdi
; CHECK-NEXT:    setne %al
; CHECK-NEXT:    retq

-> FAIL

Proposed solution:
-du option: Drop all test checks and then regenerate them.

[xbolva00]

Hit this issue some time ago in llc area, but I can port it to others..

[lebedev.ri]

This is hard-coding CHECK prefix, it wouldn't work for any other prefix,
even if it's specified for FileCheck. Though even then if you re-use the prefixes
from FileCheck, it still will leave check lines that are no longer check
lines because that prefix is no longer mentioned in FileCheck.

In other words, i'm personally honestly not seeing usefulness of this.

utils/update_llc_test_checks.py

parser.add_argument(
       help='Always use additional regex to further reduce diffs between various subtargets')
   parser.add_argument(
       '--x86_scrub_rip', action='store_true', default=True,
       help='Use more regex for x86 matching to reduce diffs between various subtargets')
   parser.add_argument(
       '--no_x86_scrub_rip', action='store_false', dest='x86_scrub_rip')
   parser.add_argument('-u', '--update-only', action='store_true',
                       help='Only update test if it was already autogened')
+  parser.add_argument('-du', '--drop-update', action='store_true',
+                      help='Drop and update test checks')
   parser.add_argument('tests', nargs='+')
   args = parser.parse_args()
 
   script_name = os.path.basename(__file__)
   autogenerated_note = (ADVERT + 'utils/' + script_name)
 
   test_paths = [test for pattern in args.tests for test in glob.glob(pattern)]
   for test in test_paths:
for test in test_paths:
     is_in_function_start = False
     func_name = None
     prefix_set = set([prefix for p in run_list for prefix in p[0]])
     if args.verbose:
       print('Rewriting FileCheck prefixes: %s' % (prefix_set,), file=sys.stderr)
     output_lines = []
     output_lines.append(autogenerated_note)
 
+    if args.drop_update:
+      input_lines = [l for l in input_lines if not l.startswith((";CHECK", "; CHECK"))]
+    
     for input_line in input_lines:
       if is_in_function_start:
         if input_line == '':
           continue
         if input_line.lstrip().startswith(';'):
           m = common.CHECK_RE.match(input_line)
           if not m or m.group(1) not in prefix_set:
             output_lines.append(input_line)