diff --git a/compiler-rt/docs/TestingGuide.rst b/compiler-rt/docs/TestingGuide.rst
--- a/compiler-rt/docs/TestingGuide.rst
+++ b/compiler-rt/docs/TestingGuide.rst
@@ -31,23 +31,24 @@
 
 Sometimes it is necessary to restrict a test to a specific target or mark it as
 an "expected fail" or XFAIL. This is normally achieved using ``REQUIRES:`` or
-``XFAIL:`` with a substring of LLVM's default target triple. Unfortunately, the
+``XFAIL:`` and the ``target=<target-triple>`` feature, typically with a regular
+expression matching an appropriate substring of the triple. Unfortunately, the
 behaviour of this is somewhat quirky in compiler-rt. There are two main
 pitfalls to avoid.
 
-The first pitfall is that these directives perform a substring match on the
-triple and as such ``XFAIL: mips`` affects more triples than expected. For
-example, ``mips-linux-gnu``, ``mipsel-linux-gnu``, ``mips64-linux-gnu``, and
-``mips64el-linux-gnu`` will all match a ``XFAIL: mips`` directive. Including a
-trailing ``-`` such as in ``XFAIL: mips-`` can help to mitigate this quirk but
-even that has issues as described below.
+The first pitfall is that these regular expressions may inadvertently match
+more triples than expected. For example, ``XFAIL: target=mips{{.*}}`` matches
+``mips-linux-gnu``, ``mipsel-linux-gnu``, ``mips64-linux-gnu``, and
+``mips64el-linux-gnu``. Including a trailing ``-`` such as in 
+``XFAIL: target=mips-{{.*}}`` can help to mitigate this quirk but even that has
+issues as described below.
 
 The second pitfall is that the default target triple is often inappropriate for
 compiler-rt tests since compiler-rt tests may be compiled for multiple targets.
 For example, a typical build on an ``x86_64-linux-gnu`` host will often run the
-tests for both x86_64 and i386. In this situation ``XFAIL: x86_64`` will mark
-both the x86_64 and i386 tests as an expected failure while ``XFAIL: i386``
-will have no effect at all.
+tests for both x86_64 and i386. In this situation ``XFAIL: target=x86_64{{{.*}}``
+will mark both the x86_64 and i386 tests as an expected failure while 
+``XFAIL: target=i386{{.*}}`` will have no effect at all.
 
 To remedy both pitfalls, compiler-rt tests provide a feature string which can
 be used to specify a single target. This string is of the form
diff --git a/llvm/docs/TestingGuide.rst b/llvm/docs/TestingGuide.rst
--- a/llvm/docs/TestingGuide.rst
+++ b/llvm/docs/TestingGuide.rst
@@ -499,10 +499,10 @@
 
     ; This test will be only enabled in the build with asserts.
     ; REQUIRES: asserts
-    ; This test is disabled on Linux.
-    ; UNSUPPORTED: -linux-
-    ; This test is expected to fail on PowerPC.
-    ; XFAIL: powerpc
+    ; This test is disabled when running on Linux.
+    ; UNSUPPORTED: system-linux
+    ; This test is expected to fail when targeting PowerPC.
+    ; XFAIL: target=powerpc{{.*}}
 
 ``REQUIRES`` and ``UNSUPPORTED`` and ``XFAIL`` all accept a comma-separated
 list of boolean expressions. The values in each expression may be:
@@ -513,7 +513,10 @@
   expression is satisfied if any feature matches the regular expression. Regular
   expressions can appear inside an identifier, so for example ``he{{l+}}o`` would match
   ``helo``, ``hello``, ``helllo``, and so on.
-- Substrings of the target triple (``UNSUPPORTED`` and ``XFAIL`` only).
+- The default target triple, preceded by the string ``target=`` (for example,
+  ``target=x86_64-pc-windows-msvc``). Typically regular expressions are used
+  to match parts of the triple (for example, ``target={{.*}}-windows{{.*}}``
+  to match any Windows target triple).
 
 | ``REQUIRES`` enables the test if all expressions are true.
 | ``UNSUPPORTED`` disables the test if any expression is true.
@@ -523,11 +526,11 @@
 
 .. code-block:: llvm
 
-    ; This test is disabled on Windows,
-    ; and is disabled on Linux, except for Android Linux.
-    ; UNSUPPORTED: windows, linux && !android
-    ; This test is expected to fail on both PowerPC and ARM.
-    ; XFAIL: powerpc || arm
+    ; This test is disabled when running on Windows,
+    ; and is disabled when targeting Linux, except for Android Linux.
+    ; UNSUPPORTED: system-windows, target={{.*linux.*}} && !target={{.*android.*}}
+    ; This test is expected to fail when targeting PowerPC or running on Darwin.
+    ; XFAIL: target=powerpc{{.*}}, system-darwin
 
 
 Substitutions