diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -614,6 +614,7 @@
     assert isinstance(cmd, ShUtil.Pipeline)
 
     procs = []
+    negate_procs = []
     default_stdin = subprocess.PIPE
     stderrTempFiles = []
     opened_files = []
@@ -659,6 +660,12 @@
                 if not args:
                     raise InternalShellError(j, "Error: 'not' requires a"
                                                 " subcommand")
+            elif args[0] == '!':
+                not_args.append(args.pop(0))
+                not_count += 1
+                if not args:
+                    raise InternalShellError(j, "Error: '!' requires a"
+                                                " subcommand")
             else:
                 break
 
@@ -705,7 +712,15 @@
         # the assumptions that (1) environment variables are not intended to be
         # relevant to 'not' commands and (2) the 'env' command should always
         # blindly pass along the status it receives from any command it calls.
-        args = not_args + args
+
+        # For plain negations, either 'not' without '--crash', or the shell
+        # operator '!', leave them out from the command to execute and
+        # invert the result code afterwards.
+        if not_crash:
+            args = not_args + args
+            not_count = 0
+        else:
+            not_args = []
 
         stdin, stdout, stderr = processRedirects(j, default_stdin, cmd_shenv,
                                                  opened_files)
@@ -769,6 +784,7 @@
                                           stderr = stderr,
                                           env = cmd_shenv.env,
                                           close_fds = kUseCloseFDs))
+            negate_procs.append((not_count % 2) != 0)
             # Let the helper know about this process
             timeoutHelper.addProcess(procs[-1])
         except OSError as e:
@@ -821,6 +837,8 @@
         # Detect Ctrl-C in subprocess.
         if res == -signal.SIGINT:
             raise KeyboardInterrupt
+        if negate_procs[i]:
+            res = not res
 
         # Ensure the resulting output is always of string type.
         try:
diff --git a/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-args-nested-none.txt b/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-args-nested-none.txt
new file mode 100644
--- /dev/null
+++ b/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-args-nested-none.txt
@@ -0,0 +1 @@
+# RUN: ! ! !
diff --git a/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-args-none.txt b/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-args-none.txt
new file mode 100644
--- /dev/null
+++ b/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-args-none.txt
@@ -0,0 +1 @@
+# RUN: !
diff --git a/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-calls-external.txt b/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-calls-external.txt
new file mode 100644
--- /dev/null
+++ b/llvm/utils/lit/tests/Inputs/shtest-not/exclamation-calls-external.txt
@@ -0,0 +1,9 @@
+# Simple uses of '!'
+
+# RUN: ! %{python} fail.py
+# RUN: ! ! %{python} pass.py
+# RUN: ! ! ! %{python} fail.py
+# RUN: ! ! ! ! %{python} pass.py
+
+# pass.py succeeds but we expect failure
+# RUN: ! %{python} pass.py
diff --git a/llvm/utils/lit/tests/lit.cfg b/llvm/utils/lit/tests/lit.cfg
--- a/llvm/utils/lit/tests/lit.cfg
+++ b/llvm/utils/lit/tests/lit.cfg
@@ -95,7 +95,8 @@
 # that might not be present or behave correctly on all platforms.  Don't do
 # this for 'echo' because an external version is used when it appears in a
 # pipeline.  Don't do this for ':' because it doesn't appear to be a valid file
-# name under Windows.
+# name under Windows. Don't do this for 'not' because lit uses the external
+# 'not' throughout a RUN line that calls 'not --crash'.
 test_bin = os.path.join(os.path.dirname(__file__), 'Inputs', 'fake-externals')
 config.environment['PATH'] = os.path.pathsep.join((test_bin,
                                                    config.environment['PATH']))
diff --git a/llvm/utils/lit/tests/shtest-not.py b/llvm/utils/lit/tests/shtest-not.py
--- a/llvm/utils/lit/tests/shtest-not.py
+++ b/llvm/utils/lit/tests/shtest-not.py
@@ -10,7 +10,27 @@
 
 # Make sure not and env commands are included in printed commands.
 
-# CHECK: -- Testing: 13 tests{{.*}}
+# CHECK: -- Testing: 16 tests{{.*}}
+
+# CHECK: FAIL: shtest-not :: exclamation-args-nested-none.txt {{.*}}
+# CHECK: $ "!" "!" "!"
+# CHECK: Error: '!' requires a subcommand
+# CHECK: error: command failed with exit status: {{.*}}
+
+# CHECK: FAIL: shtest-not :: exclamation-args-none.txt {{.*}}
+# CHECK: $ "!"
+# CHECK: Error: '!' requires a subcommand
+# CHECK: error: command failed with exit status: {{.*}}
+
+# CHECK: FAIL: shtest-not :: exclamation-calls-external.txt {{.*}}
+
+# CHECK: $ "!" "{{[^"]*}}" "fail.py"
+# CHECK: $ "!" "!" "{{[^"]*}}" "pass.py"
+# CHECK: $ "!" "!" "!" "{{[^"]*}}" "fail.py"
+# CHECK: $ "!" "!" "!" "!" "{{[^"]*}}" "pass.py"
+
+# CHECK: $ "!" "{{[^"]*}}" "pass.py"
+# CHECK: error: command failed with exit status: {{.*}}
 
 # CHECK: FAIL: shtest-not :: not-args-last-is-crash.txt {{.*}}
 # CHECK: $ "not" "--crash"
@@ -114,5 +134,5 @@
 # CHECK: error: command failed with exit status: {{.*}}
 
 # CHECK: Passed:  1
-# CHECK: Failed: 12
+# CHECK: Failed: 15
 # CHECK-NOT: {{.}}