Index: cfe/trunk/include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticDriverKinds.td
+++ cfe/trunk/include/clang/Basic/DiagnosticDriverKinds.td
@@ -187,4 +187,11 @@
 
 def warn_drv_invoking_fallback : Warning<"falling back to %0">,
   InGroup<Fallback>;
+
+def warn_target_unsupported_nan2008 : Warning<
+  "ignoring '-mnan=2008' option because the '%0' architecture does not support it">,
+  InGroup<UnsupportedNan>;
+def warn_target_unsupported_nanlegacy : Warning<
+  "ignoring '-mnan=legacy' option because the '%0' architecture does not support it">,
+  InGroup<UnsupportedNan>;
 }
Index: cfe/trunk/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticGroups.td
+++ cfe/trunk/include/clang/Basic/DiagnosticGroups.td
@@ -45,6 +45,7 @@
 def EnumConversion : DiagGroup<"enum-conversion">;
 def FloatConversion : DiagGroup<"float-conversion">;
 def EnumTooLarge : DiagGroup<"enum-too-large">;
+def UnsupportedNan : DiagGroup<"unsupported-nan">;
 def NonLiteralNullConversion : DiagGroup<"non-literal-null-conversion">;
 def NullConversion : DiagGroup<"null-conversion">;
 def ImplicitConversionFloatingPointToBool :
Index: cfe/trunk/lib/Driver/Tools.h
===================================================================
--- cfe/trunk/lib/Driver/Tools.h
+++ cfe/trunk/lib/Driver/Tools.h
@@ -234,6 +234,11 @@
 }
 
 namespace mips {
+  typedef enum {
+    NanLegacy = 1,
+    Nan2008 = 2
+  } NanEncoding;
+  NanEncoding getSupportedNanEncoding(StringRef &CPU);
   void getMipsCPUAndABI(const llvm::opt::ArgList &Args,
                         const llvm::Triple &Triple, StringRef &CPUName,
                         StringRef &ABIName);
Index: cfe/trunk/lib/Driver/Tools.cpp
===================================================================
--- cfe/trunk/lib/Driver/Tools.cpp
+++ cfe/trunk/lib/Driver/Tools.cpp
@@ -1118,11 +1118,21 @@
 
   if (Arg *A = Args.getLastArg(options::OPT_mnan_EQ)) {
     StringRef Val = StringRef(A->getValue());
-    if (Val == "2008")
-      Features.push_back("+nan2008");
-    else if (Val == "legacy")
-      Features.push_back("-nan2008");
-    else
+    if (Val == "2008") {
+      if (mips::getSupportedNanEncoding(CPUName) & mips::Nan2008)
+        Features.push_back("+nan2008");
+      else {
+        Features.push_back("-nan2008");
+        D.Diag(diag::warn_target_unsupported_nan2008) << CPUName;
+      }
+    } else if (Val == "legacy") {
+      if (mips::getSupportedNanEncoding(CPUName) & mips::NanLegacy)
+        Features.push_back("-nan2008");
+      else {
+        Features.push_back("+nan2008");
+        D.Diag(diag::warn_target_unsupported_nanlegacy) << CPUName;
+      }
+    } else
       D.Diag(diag::err_drv_unsupported_option_argument)
           << A->getOption().getName() << Val;
   }
@@ -5637,6 +5647,26 @@
     CmdArgs.push_back(LinkFlag);
 }
 
+mips::NanEncoding mips::getSupportedNanEncoding(StringRef &CPU) {
+  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 mips::hasMipsAbiArg(const ArgList &Args, const char *Value) {
   Arg *A = Args.getLastArg(options::OPT_mabi_EQ);
   return A && (A->getValue() == StringRef(Value));
Index: cfe/trunk/test/CodeGen/mips-unsupported-nan.c
===================================================================
--- cfe/trunk/test/CodeGen/mips-unsupported-nan.c
+++ cfe/trunk/test/CodeGen/mips-unsupported-nan.c
@@ -0,0 +1,25 @@
+// 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-NANLEGACY %s
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips3 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS3 -check-prefix=CHECK-NANLEGACY %s
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips4 -emit-llvm -S %s -o - 2>&1 | FileCheck -check-prefix=CHECK-MIPS4 -check-prefix=CHECK-NANLEGACY %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-NANLEGACY %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-NANLEGACY %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-NAN2008 %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-NAN2008 %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-NANLEGACY %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-NANLEGACY %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-NAN2008 %s
+
+// CHECK-MIPS2: warning: ignoring '-mnan=2008' option because the 'mips2' architecture does not support it
+// CHECK-MIPS3: warning: ignoring '-mnan=2008' option because the 'mips3' architecture does not support it
+// CHECK-MIPS4: warning: ignoring '-mnan=2008' option because the 'mips4' 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-NANLEGACY: float 0x7FF4000000000000
+// CHECK-NAN2008: float 0x7FF8000000000000
+
+float f =  __builtin_nan("");
Index: cfe/trunk/test/Driver/mips-features.c
===================================================================
--- cfe/trunk/test/Driver/mips-features.c
+++ cfe/trunk/test/Driver/mips-features.c
@@ -105,13 +105,13 @@
 // CHECK-NOMFP64: "-target-feature" "-fp64"
 //
 // -mnan=2008
-// RUN: %clang -target mips-linux-gnu -### -c %s \
+// RUN: %clang -target mips-linux-gnu -march=mips32r3 -### -c %s \
 // RUN:     -mnan=legacy -mnan=2008 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NAN2008 %s
 // CHECK-NAN2008: "-target-feature" "+nan2008"
 //
 // -mnan=legacy
-// RUN: %clang -target mips-linux-gnu -### -c %s \
+// RUN: %clang -target mips-linux-gnu -march=mips32r3 -### -c %s \
 // RUN:     -mnan=2008 -mnan=legacy 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NANLEGACY %s
 // CHECK-NANLEGACY: "-target-feature" "-nan2008"
Index: cfe/trunk/test/Driver/mips-integrated-as.s
===================================================================
--- cfe/trunk/test/Driver/mips-integrated-as.s
+++ cfe/trunk/test/Driver/mips-integrated-as.s
@@ -62,7 +62,7 @@
 // NAN-LEGACY: -cc1as
 // NAN-LEGACY: "-target-feature" "-nan2008"
 
-// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mnan=2008 2>&1 | \
+// RUN: %clang -target mips-linux-gnu -march=mips32r6 -### -fintegrated-as -c %s -mnan=2008 2>&1 | \
 // RUN:   FileCheck -check-prefix=NAN-2008 %s
 // NAN-2008: -cc1as
 // NAN-2008: "-target-feature" "+nan2008"
Index: cfe/trunk/test/Preprocessor/init.c
===================================================================
--- cfe/trunk/test/Preprocessor/init.c
+++ cfe/trunk/test/Preprocessor/init.c
@@ -4416,11 +4416,16 @@
 // RUN:   | FileCheck -check-prefix MIPS-MSA %s
 // MIPS-MSA:#define __mips_msa 1
 //
-// RUN: %clang_cc1 -target-feature +nan2008 \
+// RUN: %clang_cc1 -target-cpu mips32r3 -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-cpu mips32r3 -target-feature -nan2008 \
+// RUN:   -E -dM -triple=mips-none-none < /dev/null \
+// RUN:   | FileCheck -check-prefix NOMIPS-NAN2008 %s
+// NOMIPS-NAN2008-NOT:#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