Index: docs/LanguageExtensions.rst
===================================================================
--- docs/LanguageExtensions.rst
+++ docs/LanguageExtensions.rst
@@ -1728,6 +1728,24 @@
 
 Query for this feature with ``__has_builtin(__builtin_add_overflow)``, etc.
 
+Floating point builtins
+---------------------------------------
+
+``__builtin_canonicalize``
+--------------------------
+
+.. code-block:: c
+
+   double __builtin_canonicalize(double);
+   float __builtin_canonicalizef(float);
+   long double__builtin_canonicalizel(long double);
+
+Returns the platform specific canonical encoding of a floating point
+number. This canonicalization is useful for implementing certain
+numeric primitives such as frexp. See `LLVM canonicalize intrinsic
+<http://llvm.org/docs/LangRef.html#llvm-canonicalize-intrinsic>`_ for
+more information on the semantics.
+
 .. _langext-__c11_atomic:
 
 __c11_atomic builtins
Index: include/clang/Basic/Builtins.def
===================================================================
--- include/clang/Basic/Builtins.def
+++ include/clang/Basic/Builtins.def
@@ -377,6 +377,11 @@
 BUILTIN(__builtin_signbitf, "if", "Fnc")
 BUILTIN(__builtin_signbitl, "iLd", "Fnc")
 
+// Special FP builtins.
+BUILTIN(__builtin_canonicalize, "dd", "nc")
+BUILTIN(__builtin_canonicalizef, "ff", "nc")
+BUILTIN(__builtin_canonicalizel, "LdLd", "nc")
+
 // Builtins for arithmetic.
 BUILTIN(__builtin_clzs , "iUs"  , "nc")
 BUILTIN(__builtin_clz  , "iUi"  , "nc")
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -2138,6 +2138,11 @@
   case Builtin::BIprintf:
     if (getLangOpts().CUDA && getLangOpts().CUDAIsDevice)
       return EmitCUDADevicePrintfCallExpr(E, ReturnValue);
+    break;
+  case Builtin::BI__builtin_canonicalize:
+  case Builtin::BI__builtin_canonicalizef:
+  case Builtin::BI__builtin_canonicalizel:
+    return RValue::get(emitUnaryBuiltin(*this, E, Intrinsic::canonicalize));
   }
 
   // If this is an alias for a lib function (e.g. __builtin_sin), emit
Index: test/CodeGen/builtins.c
===================================================================
--- test/CodeGen/builtins.c
+++ test/CodeGen/builtins.c
@@ -250,6 +250,13 @@
   // CHECK: call float @llvm.fabs.f32(float
   // CHECK: call double @llvm.fabs.f64(double
   // CHECK: call x86_fp80 @llvm.fabs.f80(x86_fp80
+
+  resf = __builtin_canonicalizef(F);
+  resd = __builtin_canonicalize(D);
+  resld = __builtin_canonicalizel(LD);
+  // CHECK: call float @llvm.canonicalize.f32(float
+  // CHECK: call double @llvm.canonicalize.f64(double
+  // CHECK: call x86_fp80 @llvm.canonicalize.f80(x86_fp80
 }
 
 // __builtin_longjmp isn't supported on all platforms, so only test it on X86.