[mips] Pass nan2008 info to the back-end.

[matheusalmeida]

Summary

The initial support for NaN2008 was added to the back-end in r206396.

[atanasyan]

LGTM

[matheusalmeida]

Remove FIXME. The driver now aborts if there's a called to diag.

[atanasyan]

lib/Driver/Tools.cpp

1047

Please align this line properly:

D.Diag(diag::err_drv_unsupported_option_argument)
  << A->getOption().getName() << Val;

[matheusalmeida]

lib/Driver/Tools.cpp

1047

That was actually aligned by clang-format. See for yourself =)

[atanasyan]

lib/Driver/Tools.cpp

1047

OK :)

lib/Basic/Targets.cpp

for (std::vector<std::string>::iterator it = Features.begin(),
         IsNan2008 = true;
     }
 
     // Remove front-end specific options.
     std::vector<std::string>::iterator it =
       std::find(Features.begin(), Features.end(), "+soft-float");
     if (it != Features.end())
       Features.erase(it);
-    it = std::find(Features.begin(), Features.end(), "+nan2008");
-    if (it != Features.end())
-      Features.erase(it);
 
     setDescriptionString();
 
     return true;
   }
 
   int getEHDataRegisterNumber(unsigned RegNo) const override {
     if (RegNo == 0) return 4;

lib/Driver/Tools.cpp

static void getMIPSTargetFeatures(const Driver &D, const ArgList &Args,
   if (FloatABI == "soft") {
     // FIXME: Note, this is a hack. We need to pass the selected float
     // mode to the MipsTargetInfoBase to define appropriate macros there.
     // Now it is the only method.
     Features.push_back("+soft-float");
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_mnan_EQ)) {
-    if (StringRef(A->getValue()) == "2008")
+    StringRef Val = StringRef(A->getValue());
+    if (Val == "2008")
       Features.push_back("+nan2008");
+    else if (Val == "legacy")
+      Features.push_back("-nan2008");
+    else
+      D.Diag(diag::err_drv_unsupported_option_argument)
+          << A->getOption().getName() << Val;
   }
 
   AddTargetFeature(Args, Features, options::OPT_msingle_float,
                    options::OPT_mdouble_float, "single-float");
   AddTargetFeature(Args, Features, options::OPT_mips16, options::OPT_mno_mips16,
                    "mips16");
   AddTargetFeature(Args, Features, options::OPT_mmicromips,
                    options::OPT_mno_micromips, "micromips");

test/Driver/mips-features.c

 // CHECK-MFP64: "-target-feature" "+fp64"
 //
 // -mfp32
 // RUN: %clang -target mips-linux-gnu -### -c %s \
 // RUN:     -mfp64 -mfp32 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NOMFP64 %s
 // CHECK-NOMFP64: "-target-feature" "-fp64"
 //
+// -mnan=2008
+// RUN: %clang -target mips-linux-gnu -### -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:     -mnan=2008 -mnan=legacy 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NANLEGACY %s
+// CHECK-NANLEGACY: "-target-feature" "-nan2008"
+//
 // -mxgot
 // RUN: %clang -target mips-linux-gnu -### -c %s \
 // RUN:     -mno-xgot -mxgot 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-XGOT %s
 // CHECK-XGOT: "-mllvm" "-mxgot"
 //
 // -mno-xgot
 // RUN: %clang -target mips-linux-gnu -### -c %s \