[UpdateTestChecks] Emit warning when invalid value for -check-prefix(es) option

Summary:
The script is silent for the following issue:
FileCheck %s -check-prefix=CHECK,POPCOUNT

FileCheck will catch it later, but I think we can warn here too.

Now it warns:
 ./update_llc_test_checks.py file.ll 
WARNING: Supplied prefix 'CHECK,POPCOUNT' is invalid. Prefix must contain only alphanumeric characters, hyphens and underscores. Did you mean --check-prefixes=CHECK,POPCOUNT?



Reviewers: lebedev.ri, spatel, RKSimon, craig.topper, nikic, gbedwell

Reviewed By: RKSimon

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64589

llvm-svn: 367244
diff --git a/llvm/utils/update_mca_test_checks.py b/llvm/utils/update_mca_test_checks.py
index 87ac19b..bbeca1d 100755
--- a/llvm/utils/update_mca_test_checks.py
+++ b/llvm/utils/update_mca_test_checks.py
@@ -116,6 +116,7 @@
       _warn('could not split tool and filecheck commands: {}'.format(run_line))
       continue
 
+    common.verify_filecheck_prefixes(filecheck_cmd)
     tool_basename = os.path.splitext(os.path.basename(args.llvm_mca_binary))[0]
 
     if not tool_cmd.startswith(tool_basename + ' '):