Index: include/llvm/Support/FileCheck.h
===================================================================
--- include/llvm/Support/FileCheck.h
+++ include/llvm/Support/FileCheck.h
@@ -35,6 +35,7 @@
   bool AllowDeprecatedDagOverlap = false;
   bool Verbose = false;
   bool VerboseVerbose = false;
+  bool Warn = false;
 };
 
 
@@ -218,6 +219,8 @@
   /// Returns false if the input fails to satisfy the checks.
   bool CheckInput(SourceMgr &SM, StringRef Buffer,
                   ArrayRef<FileCheckString> CheckStrings);
+
+  void PrintWarning(SourceMgr &SM, SMLoc Loc, const Twine &Msg);
 };
 } // namespace llvm
 #endif
Index: lib/Support/FileCheck.cpp
===================================================================
--- lib/Support/FileCheck.cpp
+++ lib/Support/FileCheck.cpp
@@ -25,6 +25,13 @@
 
 using namespace llvm;
 
+void FileCheck::PrintWarning(SourceMgr &SM, SMLoc Loc, const Twine &Msg) {
+  if (!Req.Warn)
+    return;
+
+  SM.PrintMessage(Loc, SourceMgr::DK_Warning, Msg);
+}
+
 /// Parses the given string into the Pattern.
 ///
 /// \p Prefix provides which prefix is being matched, \p SM provides the
Index: test/FileCheck/check-warning.txt
===================================================================
--- /dev/null
+++ test/FileCheck/check-warning.txt
@@ -0,0 +1,10 @@
+; RUN: FileCheck -v -warn -input-file %s %s 2>&1 | FileCheck -check-prefix=CHECK-WARNING %s
+; RUN: FileCheck -v -warn=true -input-file %s %s 2>&1 | FileCheck -check-prefix=CHECK-WARNING %s
+; RUN: FileCheck -v -warn=false -input-file %s %s 2>&1 | FileCheck -check-prefix=CHECK-QUIET %s
+
+hello world
+
+; CHECK: hello world
+
+; CHECK-WARNING:   warning: Running FileCheck with warnings enabled
+; CHECK-QUIET-NOT: warning: Running FileCheck with warnings enabled
Index: utils/FileCheck/FileCheck.cpp
===================================================================
--- utils/FileCheck/FileCheck.cpp
+++ utils/FileCheck/FileCheck.cpp
@@ -85,6 +85,10 @@
     "vv", cl::init(false),
     cl::desc("Print information helpful in diagnosing internal FileCheck\n"
              "issues.  Implies -v.\n"));
+
+static cl::opt<bool> Warn("warn", cl::init(false),
+                          cl::desc("Print warning messages.\n"));
+
 static const char * DumpInputEnv = "FILECHECK_DUMP_INPUT_ON_FAILURE";
 
 static cl::opt<bool> DumpInputOnFailure(
@@ -130,6 +134,7 @@
   Req.AllowEmptyInput = AllowEmptyInput;
   Req.EnableVarScope = EnableVarScope;
   Req.AllowDeprecatedDagOverlap = AllowDeprecatedDagOverlap;
+  Req.Warn = Warn;
   Req.Verbose = Verbose;
   Req.VerboseVerbose = VerboseVerbose;
   Req.NoCanonicalizeWhiteSpace = NoCanonicalizeWhiteSpace;
@@ -157,7 +162,6 @@
     return 2;
   }
 
-
   SourceMgr SM;
 
   // Read the expected strings from the check file.
@@ -204,6 +208,9 @@
                             InputFileText, InputFile.getBufferIdentifier()),
                         SMLoc());
 
+  if (Req.Verbose)
+    FC.PrintWarning(SM, SMLoc(), "Running FileCheck with warnings enabled");
+
   int ExitCode =
       FC.CheckInput(SM, InputFileText, CheckStrings) ? EXIT_SUCCESS : 1;
   if (ExitCode == 1 && DumpInputOnFailure)