diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index c1b9d57..93d49b0 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -202,6 +202,20 @@
                         ConstSuffix);
 }
 
+/// Get the value the ATOMIC_*_LOCK_FREE macro should have for a type with
+/// the specified properties.
+static const char *getLockFreeValue(unsigned TypeWidth, unsigned TypeAlign,
+                                    unsigned InlineWidth) {
+  // Fully-aligned, power-of-2 sizes no larger than the inline
+  // width will be inlined as lock-free operations.
+  if (TypeWidth == TypeAlign && (TypeWidth & (TypeWidth - 1)) == 0 &&
+      TypeWidth <= InlineWidth)
+    return "2"; // "always lock free"
+  // We cannot be certain what operations the lib calls might be
+  // able to implement as lock-free on future processors.
+  return "1"; // "sometimes lock free"
+}
+
 /// \brief Add definitions required for a smooth interaction between
 /// Objective-C++ automated reference counting and libstdc++ (4.2).
 static void AddObjCXXARCLibstdcxxDefines(const LangOptions &LangOpts, 
@@ -521,6 +535,32 @@
   else
     Builder.defineMacro("__GNUC_STDC_INLINE__");
 
+  // The value written by __atomic_test_and_set.
+  // FIXME: This is target-dependent.
+  Builder.defineMacro("__GCC_ATOMIC_TEST_AND_SET_TRUEVAL", "1");
+
+  // Used by libstdc++ to implement ATOMIC_<foo>_LOCK_FREE.
+  unsigned InlineWidthBits = TI.getMaxAtomicInlineWidth();
+#define DEFINE_LOCK_FREE_MACRO(TYPE, Type) \
+  Builder.defineMacro("__GCC_ATOMIC_" #TYPE "_LOCK_FREE", \
+                      getLockFreeValue(TI.get##Type##Width(), \
+                                       TI.get##Type##Align(), \
+                                       InlineWidthBits));
+  DEFINE_LOCK_FREE_MACRO(BOOL, Bool);
+  DEFINE_LOCK_FREE_MACRO(CHAR, Char);
+  DEFINE_LOCK_FREE_MACRO(CHAR16_T, Char16);
+  DEFINE_LOCK_FREE_MACRO(CHAR32_T, Char32);
+  DEFINE_LOCK_FREE_MACRO(WCHAR_T, WChar);
+  DEFINE_LOCK_FREE_MACRO(SHORT, Short);
+  DEFINE_LOCK_FREE_MACRO(INT, Int);
+  DEFINE_LOCK_FREE_MACRO(LONG, Long);
+  DEFINE_LOCK_FREE_MACRO(LLONG, LongLong);
+  Builder.defineMacro("__GCC_ATOMIC_POINTER_LOCK_FREE",
+                      getLockFreeValue(TI.getPointerWidth(0),
+                                       TI.getPointerAlign(0),
+                                       InlineWidthBits));
+#undef DEFINE_LOCK_FREE_MACRO
+
   if (LangOpts.NoInlineDefine)
     Builder.defineMacro("__NO_INLINE__");