Index: llvm/trunk/include/llvm/Support/Compiler.h
===================================================================
--- llvm/trunk/include/llvm/Support/Compiler.h
+++ llvm/trunk/include/llvm/Support/Compiler.h
@@ -33,14 +33,19 @@
 # define __has_builtin(x) 0
 #endif
 
-/// \macro __GNUC_PREREQ
-/// \brief Defines __GNUC_PREREQ if glibc's features.h isn't available.
-#ifndef __GNUC_PREREQ
-# if defined(__GNUC__) && defined(__GNUC_MINOR__)
-#  define __GNUC_PREREQ(maj, min) \
-    ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
+/// \macro LLVM_GNUC_PREREQ
+/// \brief Extend the default __GNUC_PREREQ even if glibc's features.h isn't
+/// available.
+#ifndef LLVM_GNUC_PREREQ
+# if defined(__GNUC__) && defined(__GNUC_MINOR__) && defined(__GNUC_PATCHLEVEL__)
+#  define LLVM_GNUC_PREREQ(maj, min, patch) \
+    ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) + __GNUC_PATCHLEVEL__ >= \
+     ((maj) << 20) + ((min) << 10) + (patch))
+# elif defined(__GNUC__) && defined(__GNUC_MINOR__)
+#  define LLVM_GNUC_PREREQ(maj, min, patch) \
+    ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) >= ((maj) << 20) + ((min) << 10))
 # else
-#  define __GNUC_PREREQ(maj, min) 0
+#  define LLVM_GNUC_PREREQ(maj, min, patch) 0
 # endif
 #endif
 
@@ -72,8 +77,7 @@
 /// Sadly, this is separate from just r-value reference support because GCC
 /// implemented everything but this thus far. No release of GCC yet has support
 /// for this feature so it is enabled with Clang only.
-/// FIXME: This should change to a version check when GCC grows support for it.
-#if __has_feature(cxx_rvalue_references)
+#if __has_feature(cxx_rvalue_references) || LLVM_GNUC_PREREQ(4, 8, 1)
 #define LLVM_HAS_RVALUE_REFERENCE_THIS 1
 #else
 #define LLVM_HAS_RVALUE_REFERENCE_THIS 0
@@ -128,20 +132,20 @@
 /// not accessible from outside it.  Can also be used to mark variables and
 /// functions, making them private to any shared library they are linked into.
 /// On PE/COFF targets, library visibility is the default, so this isn't needed.
-#if (__has_attribute(visibility) || __GNUC_PREREQ(4, 0)) &&                    \
+#if (__has_attribute(visibility) || LLVM_GNUC_PREREQ(4, 0, 0)) &&              \
     !defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32)
 #define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
 #else
 #define LLVM_LIBRARY_VISIBILITY
 #endif
 
-#if __has_attribute(used) || __GNUC_PREREQ(3, 1)
+#if __has_attribute(used) || LLVM_GNUC_PREREQ(3, 1, 0)
 #define LLVM_ATTRIBUTE_USED __attribute__((__used__))
 #else
 #define LLVM_ATTRIBUTE_USED
 #endif
 
-#if __has_attribute(warn_unused_result) || __GNUC_PREREQ(3, 4)
+#if __has_attribute(warn_unused_result) || LLVM_GNUC_PREREQ(3, 4, 0)
 #define LLVM_ATTRIBUTE_UNUSED_RESULT __attribute__((__warn_unused_result__))
 #else
 #define LLVM_ATTRIBUTE_UNUSED_RESULT
@@ -155,14 +159,14 @@
 // more portable solution:
 //   (void)unused_var_name;
 // Prefer cast-to-void wherever it is sufficient.
-#if __has_attribute(unused) || __GNUC_PREREQ(3, 1)
+#if __has_attribute(unused) || LLVM_GNUC_PREREQ(3, 1, 0)
 #define LLVM_ATTRIBUTE_UNUSED __attribute__((__unused__))
 #else
 #define LLVM_ATTRIBUTE_UNUSED
 #endif
 
 // FIXME: Provide this for PE/COFF targets.
-#if (__has_attribute(weak) || __GNUC_PREREQ(4, 0)) &&                          \
+#if (__has_attribute(weak) || LLVM_GNUC_PREREQ(4, 0, 0)) &&                    \
     (!defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32))
 #define LLVM_ATTRIBUTE_WEAK __attribute__((__weak__))
 #else
@@ -185,7 +189,7 @@
 #define LLVM_READONLY
 #endif
 
-#if __has_builtin(__builtin_expect) || __GNUC_PREREQ(4, 0)
+#if __has_builtin(__builtin_expect) || LLVM_GNUC_PREREQ(4, 0, 0)
 #define LLVM_LIKELY(EXPR) __builtin_expect((bool)(EXPR), true)
 #define LLVM_UNLIKELY(EXPR) __builtin_expect((bool)(EXPR), false)
 #else
@@ -208,7 +212,7 @@
 
 /// LLVM_ATTRIBUTE_NOINLINE - On compilers where we have a directive to do so,
 /// mark a method "not for inlining".
-#if __has_attribute(noinline) || __GNUC_PREREQ(3, 4)
+#if __has_attribute(noinline) || LLVM_GNUC_PREREQ(3, 4, 0)
 #define LLVM_ATTRIBUTE_NOINLINE __attribute__((noinline))
 #elif defined(_MSC_VER)
 #define LLVM_ATTRIBUTE_NOINLINE __declspec(noinline)
@@ -220,7 +224,7 @@
 /// so, mark a method "always inline" because it is performance sensitive. GCC
 /// 3.4 supported this but is buggy in various cases and produces unimplemented
 /// errors, just use it in GCC 4.0 and later.
-#if __has_attribute(always_inline) || __GNUC_PREREQ(4, 0)
+#if __has_attribute(always_inline) || LLVM_GNUC_PREREQ(4, 0, 0)
 #define LLVM_ATTRIBUTE_ALWAYS_INLINE inline __attribute__((always_inline))
 #elif defined(_MSC_VER)
 #define LLVM_ATTRIBUTE_ALWAYS_INLINE __forceinline
@@ -236,7 +240,7 @@
 #define LLVM_ATTRIBUTE_NORETURN
 #endif
 
-#if __has_attribute(returns_nonnull) || __GNUC_PREREQ(4, 9)
+#if __has_attribute(returns_nonnull) || LLVM_GNUC_PREREQ(4, 9, 0)
 #define LLVM_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull))
 #else
 #define LLVM_ATTRIBUTE_RETURNS_NONNULL
@@ -268,7 +272,7 @@
 /// LLVM_BUILTIN_UNREACHABLE - On compilers which support it, expands
 /// to an expression which states that it is undefined behavior for the
 /// compiler to reach this point.  Otherwise is not defined.
-#if __has_builtin(__builtin_unreachable) || __GNUC_PREREQ(4, 5)
+#if __has_builtin(__builtin_unreachable) || LLVM_GNUC_PREREQ(4, 5, 0)
 # define LLVM_BUILTIN_UNREACHABLE __builtin_unreachable()
 #elif defined(_MSC_VER)
 # define LLVM_BUILTIN_UNREACHABLE __assume(false)
@@ -276,7 +280,7 @@
 
 /// LLVM_BUILTIN_TRAP - On compilers which support it, expands to an expression
 /// which causes the program to exit abnormally.
-#if __has_builtin(__builtin_trap) || __GNUC_PREREQ(4, 3)
+#if __has_builtin(__builtin_trap) || LLVM_GNUC_PREREQ(4, 3, 0)
 # define LLVM_BUILTIN_TRAP __builtin_trap()
 #else
 # define LLVM_BUILTIN_TRAP *(volatile int*)0x11 = 0
@@ -284,7 +288,7 @@
 
 /// \macro LLVM_ASSUME_ALIGNED
 /// \brief Returns a pointer with an assumed alignment.
-#if __has_builtin(__builtin_assume_aligned) || __GNUC_PREREQ(4, 7)
+#if __has_builtin(__builtin_assume_aligned) || LLVM_GNUC_PREREQ(4, 7, 0)
 # define LLVM_ASSUME_ALIGNED(p, a) __builtin_assume_aligned(p, a)
 #elif defined(LLVM_BUILTIN_UNREACHABLE)
 // As of today, clang does not support __builtin_assume_aligned.
Index: llvm/trunk/include/llvm/Support/MathExtras.h
===================================================================
--- llvm/trunk/include/llvm/Support/MathExtras.h
+++ llvm/trunk/include/llvm/Support/MathExtras.h
@@ -80,7 +80,7 @@
   if (ZB != ZB_Undefined && Val == 0)
     return 32;
 
-#if __has_builtin(__builtin_ctz) || __GNUC_PREREQ(4, 0)
+#if __has_builtin(__builtin_ctz) || LLVM_GNUC_PREREQ(4, 0, 0)
   return __builtin_ctz(Val);
 #elif _MSC_VER
   unsigned long Index;
@@ -95,7 +95,7 @@
   if (ZB != ZB_Undefined && Val == 0)
     return 64;
 
-#if __has_builtin(__builtin_ctzll) || __GNUC_PREREQ(4, 0)
+#if __has_builtin(__builtin_ctzll) || LLVM_GNUC_PREREQ(4, 0, 0)
   return __builtin_ctzll(Val);
 #elif _MSC_VER
   unsigned long Index;
@@ -146,7 +146,7 @@
   if (ZB != ZB_Undefined && Val == 0)
     return 32;
 
-#if __has_builtin(__builtin_clz) || __GNUC_PREREQ(4, 0)
+#if __has_builtin(__builtin_clz) || LLVM_GNUC_PREREQ(4, 0, 0)
   return __builtin_clz(Val);
 #elif _MSC_VER
   unsigned long Index;
@@ -161,7 +161,7 @@
   if (ZB != ZB_Undefined && Val == 0)
     return 64;
 
-#if __has_builtin(__builtin_clzll) || __GNUC_PREREQ(4, 0)
+#if __has_builtin(__builtin_clzll) || LLVM_GNUC_PREREQ(4, 0, 0)
   return __builtin_clzll(Val);
 #elif _MSC_VER
   unsigned long Index;