Index: docs/LanguageExtensions.rst
===================================================================
--- docs/LanguageExtensions.rst
+++ docs/LanguageExtensions.rst
@@ -494,11 +494,12 @@
 It is recommended that portable code use the ``_Float16`` type because
 ``__fp16`` is an ARM C-Language Extension (ACLE), whereas ``_Float16`` is
 defined by the C standards committee, so using ``_Float16`` will not prevent
-code from being ported to architectures other than Arm.  Also, ``_Float16``
-arithmetic and operations will directly map on half-precision instructions when
-they are available (e.g. Armv8.2-A), avoiding conversions to/from
-single-precision, and thus will result in more performant code. If
-half-precision instructions are unavailable, values will be promoted to
+code from being ported to architectures other than Arm, though ``_Float16`` is
+currently disabled on most platforms until support is added to their published
+ABI documents. Also, ``_Float16`` arithmetic and operations will directly map on
+half-precision instructions when they are available (e.g. Armv8.2-A), avoiding
+conversions to/from single-precision, and thus will result in more performant
+code. If half-precision instructions are unavailable, values will be promoted to
 single-precision, similar to the semantics of ``__fp16`` except that the
 results will be stored in single-precision.
 
Index: include/clang/Basic/TargetInfo.h
===================================================================
--- include/clang/Basic/TargetInfo.h
+++ include/clang/Basic/TargetInfo.h
@@ -63,6 +63,7 @@
   bool HasLegalHalfType; // True if the backend supports operations on the half
                          // LLVM IR type.
   bool HasFloat128;
+  bool HasFloat16;
   unsigned char PointerWidth, PointerAlign;
   unsigned char BoolWidth, BoolAlign;
   unsigned char IntWidth, IntAlign;
@@ -516,6 +517,9 @@
   /// Determine whether the __float128 type is supported on this target.
   virtual bool hasFloat128Type() const { return HasFloat128; }
 
+  /// Determine whether the _Float16 type is supported on this target.
+  virtual bool hasFloat16Type() const { return HasFloat16; }
+
   /// Return the alignment that is suitable for storing any
   /// object with a fundamental alignment requirement.
   unsigned getSuitableAlign() const { return SuitableAlign; }
Index: lib/Basic/TargetInfo.cpp
===================================================================
--- lib/Basic/TargetInfo.cpp
+++ lib/Basic/TargetInfo.cpp
@@ -34,6 +34,7 @@
   NoAsmVariants = false;
   HasLegalHalfType = false;
   HasFloat128 = false;
+  HasFloat16 = false;
   PointerWidth = PointerAlign = 32;
   BoolWidth = BoolAlign = 8;
   IntWidth = IntAlign = 32;
Index: lib/Basic/Targets/AArch64.cpp
===================================================================
--- lib/Basic/Targets/AArch64.cpp
+++ lib/Basic/Targets/AArch64.cpp
@@ -49,6 +49,7 @@
 
   // All AArch64 implementations support ARMv8 FP, which makes half a legal type.
   HasLegalHalfType = true;
+  HasFloat16= true;
 
   LongWidth = LongAlign = PointerWidth = PointerAlign = 64;
   MaxVectorAlign = 128;
Index: lib/Basic/Targets/ARM.cpp
===================================================================
--- lib/Basic/Targets/ARM.cpp
+++ lib/Basic/Targets/ARM.cpp
@@ -396,6 +396,7 @@
   SoftFloat = SoftFloatABI = false;
   HWDiv = 0;
   DotProd = 0;
+  HasFloat16 = true;
 
   // This does not diagnose illegal cases like having both
   // "+vfpv2" and "+vfpv3" or having "+neon" and "+fp-only-sp".
Index: lib/Basic/Targets/SPIR.h
===================================================================
--- lib/Basic/Targets/SPIR.h
+++ lib/Basic/Targets/SPIR.h
@@ -47,6 +47,7 @@
     AddrSpaceMap = &SPIRAddrSpaceMap;
     UseAddrSpaceMapMangling = true;
     HasLegalHalfType = true;
+    HasFloat16= true;
     // Define available target features
     // These must be defined in sorted order!
     NoAsmVariants = true;
Index: lib/Sema/SemaType.cpp
===================================================================
--- lib/Sema/SemaType.cpp
+++ lib/Sema/SemaType.cpp
@@ -1441,7 +1441,12 @@
     else
       Result = Context.Int128Ty;
     break;
-  case DeclSpec::TST_float16: Result = Context.Float16Ty; break;
+  case DeclSpec::TST_float16:
+    if (!S.Context.getTargetInfo().hasFloat16Type())
+      S.Diag(DS.getTypeSpecTypeLoc(), diag::err_type_unsupported)
+        << "_Float16";
+    Result = Context.Float16Ty;
+    break;
   case DeclSpec::TST_half:    Result = Context.HalfTy; break;
   case DeclSpec::TST_float:   Result = Context.FloatTy; break;
   case DeclSpec::TST_double:
Index: test/AST/float16.cpp
===================================================================
--- test/AST/float16.cpp
+++ test/AST/float16.cpp
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -std=c++11 -ast-dump %s | FileCheck %s --strict-whitespace
-// RUN: %clang_cc1 -std=c++11 -ast-dump -fnative-half-type %s | FileCheck %s --check-prefix=CHECK-NATIVE --strict-whitespace
+// RUN: %clang_cc1 -std=c++11 -ast-dump -triple aarch64-linux-gnu %s | FileCheck %s --strict-whitespace
+// RUN: %clang_cc1 -std=c++11 -ast-dump -triple aarch64-linux-gnu -fnative-half-type %s | FileCheck %s --check-prefix=CHECK-NATIVE --strict-whitespace
 
 /*  Various contexts where type _Float16 can appear. */
 
Index: test/CodeGenCXX/float16-declarations.cpp
===================================================================
--- test/CodeGenCXX/float16-declarations.cpp
+++ test/CodeGenCXX/float16-declarations.cpp
@@ -1,5 +1,4 @@
 // RUN: %clang -std=c++11 --target=aarch64-arm--eabi -S -emit-llvm %s -o - | FileCheck %s  --check-prefix=CHECK --check-prefix=CHECK-AARCH64
-// RUN: %clang -std=c++11 --target=x86_64 -S -emit-llvm %s -o - | FileCheck %s  --check-prefix=CHECK --check-prefix=CHECK-X86
 
 /*  Various contexts where type _Float16 can appear. */
 
@@ -15,7 +14,6 @@
 
   _Float16 arr1n[10];
 // CHECK-AARCH64-DAG: @_ZN12_GLOBAL__N_15arr1nE = internal global [10 x half] zeroinitializer, align 2
-// CHECK-X86-DAG:     @_ZN12_GLOBAL__N_15arr1nE = internal global [10 x half] zeroinitializer, align 16
 
   _Float16 arr2n[] = { 1.2, 3.0, 3.e4 };
 // CHECK-DAG: @_ZN12_GLOBAL__N_15arr2nE = internal global [3 x half] [half 0xH3CCD, half 0xH4200, half 0xH7753], align 2
@@ -30,14 +28,12 @@
 
 _Float16 f1f;
 // CHECK-AARCH64-DAG: @f1f = dso_local global half 0xH0000, align 2
-// CHECK-X86-DAG: @f1f = dso_local global half 0xH0000, align 2
 
 _Float16 f2f = 32.4;
 // CHECK-DAG: @f2f = dso_local global half 0xH500D, align 2
 
 _Float16 arr1f[10];
 // CHECK-AARCH64-DAG: @arr1f = dso_local global [10 x half] zeroinitializer, align 2
-// CHECK-X86-DAG: @arr1f = dso_local global [10 x half] zeroinitializer, align 16
 
 _Float16 arr2f[] = { -1.2, -3.0, -3.e4 };
 // CHECK-DAG: @arr2f = dso_local global [3 x half] [half 0xHBCCD, half 0xHC200, half 0xHF753], align 2
@@ -137,8 +133,6 @@
   long double cvtld = f2n;
 //CHECK-AARCh64-DAG: [[H2LD:%[a-z0-9]+]] = fpext half {{%[0-9]+}} to fp128
 //CHECK-AARCh64-DAG: store fp128 [[H2LD]], fp128* %{{.*}}, align 16
-//CHECK-X86-DAG:     [[H2LD:%[a-z0-9]+]] = fpext half {{%[0-9]+}} to x86_fp80
-//CHECK-X86-DAG:     store x86_fp80 [[H2LD]], x86_fp80* %{{.*}}, align 16
 
   _Float16 f2h = 42.0f;
 //CHECK-DAG: store half 0xH5140, half* %{{.*}}, align 2
Index: test/CodeGenCXX/mangle-ms.cpp
===================================================================
--- test/CodeGenCXX/mangle-ms.cpp
+++ test/CodeGenCXX/mangle-ms.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -fblocks -emit-llvm %s -o - -triple=i386-pc-win32 -std=c++98 | FileCheck %s
 // RUN: %clang_cc1 -fblocks -emit-llvm %s -o - -triple=x86_64-pc-win32 -std=c++98| FileCheck -check-prefix X64 %s
+// RUN: %clang_cc1 -fblocks -emit-llvm %s -o - -triple=aarch64-pc-win32 -std=c++98 -DARM | FileCheck -check-prefixes=X64,ARM %s
 
 int a;
 // CHECK-DAG: @"?a@@3HA"
@@ -466,10 +467,12 @@
 // CHECK-DAG: define dso_local void @"?f@Complex@@YAXU?$_Complex@H@__clang@@@Z"(
 void f(_Complex int) {}
 }
+#ifdef ARM
 namespace Float16 {
-// CHECK-DAG: define dso_local void @"?f@Float16@@YAXU_Float16@__clang@@@Z"(
+// ARM-DAG: define dso_local void @"?f@Float16@@YAXU_Float16@__clang@@@Z"(
 void f(_Float16) {}
 }
+#endif // ARM
 
 namespace PR26029 {
 template <class>
Index: test/Lexer/half-literal.cpp
===================================================================
--- test/Lexer/half-literal.cpp
+++ test/Lexer/half-literal.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic -triple aarch64-linux-gnu %s
 float a = 1.0h; // expected-error{{no matching literal operator for call to 'operator""h' with argument of type 'long double' or 'const char *', and no matching literal operator template}}
 float b = 1.0H; // expected-error{{invalid suffix 'H' on floating constant}}
 
Index: test/Sema/Float16.c
===================================================================
--- /dev/null
+++ test/Sema/Float16.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -triple x86_64-linux-pc %s
+// RUN: %clang_cc1 -fsyntax-only -verify -triple spir-unknown-unknown %s -DHAVE
+// RUN: %clang_cc1 -fsyntax-only -verify -triple armv7a-linux-gnu %s -DHAVE
+// RUN: %clang_cc1 -fsyntax-only -verify -triple aarch64-linux-gnu %s -DHAVE
+
+#ifdef HAVE
+// expected-no-diagnostics
+#else
+// expected-error@+2{{_Float16 is not supported on this target}}
+#endif // HAVE
+_Float16 f;