Index: include/clang/Basic/DiagnosticCommonKinds.td
===================================================================
--- include/clang/Basic/DiagnosticCommonKinds.td
+++ include/clang/Basic/DiagnosticCommonKinds.td
@@ -142,6 +142,10 @@
     "the '%0' unit is not supported with this instruction set">;
 def err_target_unsupported_unaligned : Error<
   "the %0 sub-architecture does not support unaligned accesses">;
+def warn_target_unsupported_nan2008 : Warning<
+  "ignoring '-mnan=2008' option because the '%0' architecture does not support it">;
+def warn_target_unsupported_nanlegacy : Warning<
+  "ignoring '-mnan=legacy' option because the '%0' architecture does not support it">;
 
 // Source manager
 def err_cannot_open_file : Error<"cannot open file '%0': %1">, DefaultFatal;
Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -5737,6 +5737,10 @@
   enum DspRevEnum {
     NoDSP, DSP1, DSP2
   } DspRev;
+  typedef enum {
+    NanLegacy = 1,
+    Nan2008 = 2
+  } NanEncoding;
   bool HasMSA;
 
 protected:
@@ -5752,8 +5756,24 @@
     TheCXXABI.set(TargetCXXABI::GenericMIPS);
   }
 
-  bool isNaN2008Default() const {
-    return CPU == "mips32r6" || CPU == "mips64r6";
+  NanEncoding getSupportedNanEncoding() const {
+    return (NanEncoding)llvm::StringSwitch<int>(CPU)
+        .Case("mips1", NanLegacy)
+        .Case("mips2", NanLegacy)
+        .Case("mips3", NanLegacy)
+        .Case("mips4", NanLegacy)
+        .Case("mips5", NanLegacy)
+        .Case("mips32", NanLegacy)
+        .Case("mips32r2", NanLegacy)
+        .Case("mips32r3", NanLegacy | Nan2008)
+        .Case("mips32r5", NanLegacy | Nan2008)
+        .Case("mips32r6", Nan2008)
+        .Case("mips64", NanLegacy)
+        .Case("mips64r2", NanLegacy)
+        .Case("mips64r3", NanLegacy | Nan2008)
+        .Case("mips64r5", NanLegacy | Nan2008)
+        .Case("mips64r6", Nan2008)
+        .Default(NanLegacy);
   }
 
   bool isFP64Default() const {
@@ -5958,7 +5978,7 @@
                             DiagnosticsEngine &Diags) override {
     IsMips16 = false;
     IsMicromips = false;
-    IsNan2008 = isNaN2008Default();
+    IsNan2008 = getSupportedNanEncoding() == Nan2008;
     IsSingleFloat = false;
     FloatABI = HardFloat;
     DspRev = NoDSP;
@@ -5984,10 +6004,17 @@
         HasFP64 = true;
       else if (*it == "-fp64")
         HasFP64 = false;
-      else if (*it == "+nan2008")
-        IsNan2008 = true;
-      else if (*it == "-nan2008")
-        IsNan2008 = false;
+      else if (*it == "+nan2008") {
+        if (getSupportedNanEncoding() & Nan2008)
+          IsNan2008 = true;
+        else
+          Diags.Report(diag::warn_target_unsupported_nan2008) << CPU;
+      } else if (*it == "-nan2008") {
+        if (getSupportedNanEncoding() & NanLegacy)
+          IsNan2008 = false;
+        else
+          Diags.Report(diag::warn_target_unsupported_nanlegacy) << CPU;
+      }
     }
 
     // Remove front-end specific options.
Index: test/CodeGen/mips-unsupported-nan.c
===================================================================
--- /dev/null
+++ test/CodeGen/mips-unsupported-nan.c
@@ -0,0 +1,22 @@
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips2 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS2 -check-prefix=CHECK-LEGACY %s
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips32 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS32 -check-prefix=CHECK-LEGACY %s
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips32r2 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS32R2 -check-prefix=CHECK-LEGACY %s
+// RUN: %clang -target mipsel-unknown-linux -mnan=legacy -march=mips32r2 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-NOT-MIPS32R2 -check-prefix=CHECK-LEGACY %s
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips32r3 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-NOT-MIPS32R3 -check-prefix=CHECK-2008 %s
+// RUN: %clang -target mipsel-unknown-linux -mnan=legacy -march=mips32r6 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS32R6 -check-prefix=CHECK-2008 %s
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips64 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS64 -check-prefix=CHECK-LEGACY %s
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips64r2 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS64R2 -check-prefix=CHECK-LEGACY %s
+// RUN: %clang -target mips64el-unknown-linux -mnan=legacy -march=mips64r6 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS64R6 -check-prefix=CHECK-2008 %s
+
+// CHECK-MIPS2: warning: ignoring '-mnan=2008' option because the 'mips2' architecture does not support it
+// CHECK-MIPS32: warning: ignoring '-mnan=2008' option because the 'mips32' architecture does not support it
+// CHECK-MIPS32R2: warning: ignoring '-mnan=2008' option because the 'mips32r2' architecture does not support it
+// CHECK-MIPS32R3: warning: ignoring '-mnan=2008' option because the 'mips32r3' architecture does not support it
+// CHECK-MIPS32R6: warning: ignoring '-mnan=legacy' option because the 'mips32r6' architecture does not support it
+// CHECK-MIPS64: warning: ignoring '-mnan=2008' option because the 'mips64' architecture does not support it
+// CHECK-MIPS64R2: warning: ignoring '-mnan=2008' option because the 'mips64r2' architecture does not support it
+// CHECK-MIPS64R6: warning: ignoring '-mnan=legacy' option because the 'mips64r6' architecture does not support it
+// CHECK-LEGACY: float 0x7FF4000000000000
+// CHECK-2008: float 0x7FF8000000000000
+
+float f =  __builtin_nan("");
Index: test/Misc/warning-flags.c
===================================================================
--- test/Misc/warning-flags.c
+++ test/Misc/warning-flags.c
@@ -18,7 +18,7 @@
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (94):
+CHECK: Warnings without flags (96):
 CHECK-NEXT:   ext_excess_initializers
 CHECK-NEXT:   ext_excess_initializers_in_char_array_initializer
 CHECK-NEXT:   ext_expected_semi_decl_list
@@ -103,6 +103,8 @@
 CHECK-NEXT:   warn_register_objc_catch_parm
 CHECK-NEXT:   warn_related_result_type_compatibility_class
 CHECK-NEXT:   warn_related_result_type_compatibility_protocol
+CHECK-NEXT:   warn_target_unsupported_nan2008
+CHECK-NEXT:   warn_target_unsupported_nanlegacy
 CHECK-NEXT:   warn_template_export_unsupported
 CHECK-NEXT:   warn_template_spec_extra_headers
 CHECK-NEXT:   warn_tentative_incomplete_array
Index: test/Preprocessor/init.c
===================================================================
--- test/Preprocessor/init.c
+++ test/Preprocessor/init.c
@@ -4416,11 +4416,6 @@
 // RUN:   | FileCheck -check-prefix MIPS-MSA %s
 // MIPS-MSA:#define __mips_msa 1
 //
-// RUN: %clang_cc1 -target-feature +nan2008 \
-// RUN:   -E -dM -triple=mips-none-none < /dev/null \
-// RUN:   | FileCheck -check-prefix MIPS-NAN2008 %s
-// MIPS-NAN2008:#define __mips_nan2008 1
-//
 // RUN: %clang_cc1 -target-feature -fp64 \
 // RUN:   -E -dM -triple=mips-none-none < /dev/null \
 // RUN:   | FileCheck -check-prefix MIPS32-MFP32 %s