Index: llvm/utils/FileCheck/FileCheck.cpp
===================================================================
--- llvm/utils/FileCheck/FileCheck.cpp
+++ llvm/utils/FileCheck/FileCheck.cpp
@@ -90,8 +90,17 @@
              "provided for convenience as old tests are migrated to the new\n"
              "non-overlapping CHECK-DAG implementation.\n"));
 
+static const char * DumpInputEnv = "FILECHECK_DUMP_INPUT_ON_FAILURE";
+
+static cl::opt<const char*> DumpInputOnFailure(
+    "dump-input-on-failure", cl::init(std::getenv(DumpInputEnv)),
+    cl::desc("Dump original input to stderr before failing.\n"
+             "The value can be also controlled using\n"
+             "FILECHECK_DUMP_INPUT_ON_FAILURE environment variable.\n"));
+
 typedef cl::list<std::string>::const_iterator prefix_iterator;
 
+
 //===----------------------------------------------------------------------===//
 // Pattern Handling Code.
 //===----------------------------------------------------------------------===//
@@ -1501,5 +1510,9 @@
                             InputFileText, InputFile.getBufferIdentifier()),
                         SMLoc());
 
-  return CheckInput(SM, InputFileText, CheckStrings) ? EXIT_SUCCESS : 1;
+  int ExitCode = CheckInput(SM, InputFileText, CheckStrings) ? EXIT_SUCCESS : 1;
+  if (ExitCode == 1 && std::getenv(DumpInputEnv))
+    errs() << "Full input was:\n<<<<<<\n" << InputFileText << "\n>>>>>>\n";
+
+  return ExitCode;
 }
Index: llvm/utils/lit/lit/TestingConfig.py
===================================================================
--- llvm/utils/lit/lit/TestingConfig.py
+++ llvm/utils/lit/lit/TestingConfig.py
@@ -25,7 +25,8 @@
                      'CLANG', 'LD_PRELOAD', 'ASAN_OPTIONS', 'UBSAN_OPTIONS',
                      'LSAN_OPTIONS', 'ADB', 'ANDROID_SERIAL',
                      'SANITIZER_IGNORE_CVE_2016_2143', 'TMPDIR', 'TMP', 'TEMP',
-                     'TEMPDIR', 'AVRLIT_BOARD', 'AVRLIT_PORT']
+                     'TEMPDIR', 'AVRLIT_BOARD', 'AVRLIT_PORT',
+                     'FILECHECK_DUMP_INPUT_ON_FAILURE']
         for var in pass_vars:
             val = os.environ.get(var, '')
             # Check for empty string as some variables such as LD_PRELOAD cannot be empty