Index: llvm/trunk/docs/CommandGuide/lit.rst
===================================================================
--- llvm/trunk/docs/CommandGuide/lit.rst
+++ llvm/trunk/docs/CommandGuide/lit.rst
@@ -169,6 +169,13 @@
  must be in the range ``1..M``. The environment variable
  ``LIT_RUN_SHARD`` can also be used in place of this option.
 
+.. option:: --filter=REGEXP
+
+  Run only those tests whose name matches the regular expression specified in
+  ``REGEXP``. The environment variable ``LIT_FILTER`` can be also used in place
+  of this option, which is especially useful in environments where the call
+  to ``lit`` is issued indirectly.
+
 ADDITIONAL OPTIONS
 ------------------
 
Index: llvm/trunk/utils/lit/lit/main.py
===================================================================
--- llvm/trunk/utils/lit/lit/main.py
+++ llvm/trunk/utils/lit/lit/main.py
@@ -262,7 +262,8 @@
     selection_group.add_argument("--filter", metavar="REGEX",
                      help=("Only run tests with paths matching the given "
                            "regular expression"),
-                     action="store", default=None)
+                     action="store",
+                     default=os.environ.get("LIT_FILTER"))
     selection_group.add_argument("--num-shards", dest="numShards", metavar="M",
                      help="Split testsuite into M pieces and only run one",
                      action="store", type=int,
Index: llvm/trunk/utils/lit/tests/selecting.py
===================================================================
--- llvm/trunk/utils/lit/tests/selecting.py
+++ llvm/trunk/utils/lit/tests/selecting.py
@@ -7,6 +7,11 @@
 # RUN: %{lit} --filter 'o[a-z]e' %{inputs}/discovery | FileCheck --check-prefix=CHECK-FILTER %s
 # CHECK-FILTER: Testing: 2 of 5 tests
 
+# Check that regex-filtering based on environment variables work.
+#
+# RUN: LIT_FILTER='o[a-z]e' %{lit} %{inputs}/discovery | FileCheck --check-prefix=CHECK-FILTER-ENV %s
+# CHECK-FILTER-ENV: Testing: 2 of 5 tests
+
 
 # Check that maximum counts work
 #