diff --git a/llvm/utils/lit/lit/cl_arguments.py b/llvm/utils/lit/lit/cl_arguments.py
--- a/llvm/utils/lit/lit/cl_arguments.py
+++ b/llvm/utils/lit/lit/cl_arguments.py
@@ -109,6 +109,9 @@
             dest="maxFailures",
             help="Stop execution after the given number of failures.",
             type=_positive_int)
+    execution_group.add_argument("--allow-empty-runs",
+            help="Do not fail the run if all tests are filtered out",
+            action="store_true")
 
     selection_group = parser.add_argument_group("Test Selection")
     selection_group.add_argument("--max-tests",
diff --git a/llvm/utils/lit/lit/main.py b/llvm/utils/lit/lit/main.py
--- a/llvm/utils/lit/lit/main.py
+++ b/llvm/utils/lit/lit/main.py
@@ -43,6 +43,9 @@
         echo_all_commands = opts.echoAllCommands)
 
     tests = lit.discovery.find_tests_for_inputs(litConfig, opts.test_paths)
+    if not tests:
+        sys.stderr.write('Did not disover any tests for provided path(s).\n')
+        sys.exit(2)
 
     # Command line overrides configuration for maxIndividualTestTime.
     if opts.maxIndividualTestTime is not None:  # `not None` is important (default: 0)
@@ -63,12 +66,27 @@
 
     if opts.filter:
         tests = [t for t in tests if opts.filter.search(t.getFullName())]
+        if not tests:
+            sys.stderr.write('Filter did not match any tests '
+                             '(of %d discovered).  ' % numTotalTests)
+            if opts.allow_empty_runs:
+                sys.stderr.write('Suppressing error because '
+                                 "'--allow-empty-runs' was specified.\n")
+                sys.exit(0)
+            else:
+                sys.stderr.write("Use '--allow-empty-runs' to suppress this "
+                                 'error.\n')
+                sys.exit(2)
 
     determine_order(tests, opts.order)
 
     if opts.shard:
         (run, shards) = opts.shard
         tests = filter_by_shard(tests, run, shards, litConfig)
+        if not tests:
+            sys.stderr.write('Shard does not contain any tests.  Consider '
+                             'decreasing the number of shards.\n')
+            sys.exit(0)
 
     if opts.max_tests:
         tests = tests[:opts.max_tests]
@@ -87,7 +105,7 @@
         write_test_results_xunit(tests, opts)
 
     if litConfig.numErrors:
-        sys.stderr.write('\n%d error(s), exiting.\n' % litConfig.numErrors)
+        sys.stderr.write('\n%d error(s) in tests.\n' % litConfig.numErrors)
         sys.exit(2)
 
     if litConfig.numWarnings:
diff --git a/llvm/utils/lit/lit/run.py b/llvm/utils/lit/lit/run.py
--- a/llvm/utils/lit/lit/run.py
+++ b/llvm/utils/lit/lit/run.py
@@ -13,7 +13,7 @@
     def release(self): pass
 
 def create_run(tests, lit_config, workers, progress_callback, timeout=None):
-    # TODO(yln) assert workers > 0
+    assert workers > 0
     if workers == 1:
         return SerialRun(tests, lit_config, progress_callback, timeout)
     return ParallelRun(tests, lit_config, progress_callback, timeout, workers)
@@ -45,9 +45,6 @@
         computed. Tests which were not actually executed (for any reason) will
         be given an UNRESOLVED result.
         """
-        if not self.tests:
-            return 0.0
-
         self.failure_count = 0
         self.hit_max_failures = False
 
diff --git a/llvm/utils/lit/tests/selecting.py b/llvm/utils/lit/tests/selecting.py
--- a/llvm/utils/lit/tests/selecting.py
+++ b/llvm/utils/lit/tests/selecting.py
@@ -1,6 +1,21 @@
 # RUN: %{lit} %{inputs}/discovery | FileCheck --check-prefix=CHECK-BASIC %s
 # CHECK-BASIC: Testing: 5 tests
 
+
+# Check that we exit with an error if we do not discover any tests, even with --allow-empty-runs.
+#
+# RUN: not %{lit} %{inputs}/nonexistent                    2>&1 | FileCheck --check-prefix=CHECK-BAD-PATH %s
+# RUN: not %{lit} %{inputs}/nonexistent --allow-empty-runs 2>&1 | FileCheck --check-prefix=CHECK-BAD-PATH %s
+# CHECK-BAD-PATH: Did not disover any tests for provided path(s).
+
+# Check that we exit with an error if we filter out all tests, but allow it with --allow-empty-runs.
+#
+# RUN: not %{lit} --filter 'nonexistent'                    %{inputs}/discovery 2>&1 | FileCheck --check-prefixes=CHECK-BAD-FILTER,CHECK-BAD-FILTER-ERROR %s
+# RUN:     %{lit} --filter 'nonexistent' --allow-empty-runs %{inputs}/discovery 2>&1 | FileCheck --check-prefixes=CHECK-BAD-FILTER,CHECK-BAD-FILTER-ALLOW %s
+# CHECK-BAD-FILTER: Filter did not match any tests (of 5 discovered).
+# CHECK-BAD-FILTER-ERROR: Use '--allow-empty-runs' to suppress this error.
+# CHECK-BAD-FILTER-ALLOW: Suppressing error because '--allow-empty-runs' was specified.
+
 # Check that regex-filtering works, is case-insensitive, and can be configured via env var.
 #
 # RUN: %{lit} --filter 'o[a-z]e' %{inputs}/discovery | FileCheck --check-prefix=CHECK-FILTER %s
@@ -8,6 +23,7 @@
 # RUN: env LIT_FILTER='o[a-z]e' %{lit} %{inputs}/discovery | FileCheck --check-prefix=CHECK-FILTER %s
 # CHECK-FILTER: Testing: 2 of 5 tests
 
+
 # Check that maximum counts work
 #
 # RUN: %{lit} --max-tests 3 %{inputs}/discovery | FileCheck --check-prefix=CHECK-MAX %s
@@ -68,15 +84,13 @@
 #
 # RUN: %{lit} --num-shards 100 --run-shard 6 %{inputs}/discovery >%t.out 2>%t.err
 # RUN: FileCheck --check-prefix=CHECK-SHARD-BIG-ERR2 < %t.err %s
-# RUN: FileCheck --check-prefix=CHECK-SHARD-BIG-OUT2 < %t.out %s
 # CHECK-SHARD-BIG-ERR2: note: Selecting shard 6/100 = size 0/5 = tests #(100*k)+6 = []
-# CHECK-SHARD-BIG-OUT2: Testing: 0 of 5 tests
+# CHECK-SHARD-BIG-ERR2: Shard does not contain any tests.  Consider decreasing the number of shards.
 #
 # RUN: %{lit} --num-shards 100 --run-shard 50 %{inputs}/discovery >%t.out 2>%t.err
 # RUN: FileCheck --check-prefix=CHECK-SHARD-BIG-ERR3 < %t.err %s
-# RUN: FileCheck --check-prefix=CHECK-SHARD-BIG-OUT3 < %t.out %s
 # CHECK-SHARD-BIG-ERR3: note: Selecting shard 50/100 = size 0/5 = tests #(100*k)+50 = []
-# CHECK-SHARD-BIG-OUT3: Testing: 0 of 5 tests
+# CHECK-SHARD-BIG-ERR3: Shard does not contain any tests.  Consider decreasing the number of shards.
 
 
 # Check that range constraints are enforced