[mips] Relax -mnan=2008 acceptance to permit MIPS32R2 and MIPS64R2.

[dsanders]

Summary

Strictly speaking, the MIPS*R2 ISA's should not permit -mnan=2008 since this
feature was added in MIPS*R3. However, other toolchains permit this and we
should do the same.

[atanasyan]

LGTM

lib/Driver/Tools.cpp

void arm::appendEBLinkFlags(const ArgList &Args, ArgStringList &CmdArgs,
 
   // ARMv7 (and later) and ARMv6-M do not support BE-32, so instruct the linker
   // to generate BE-8 executables.
   if (getARMSubArchVersionNumber(Triple) >= 7 || isARMMProfile(Triple))
     CmdArgs.push_back("--be8");
 }
 
 mips::NanEncoding mips::getSupportedNanEncoding(StringRef &CPU) {
+  // Strictly speaking, mips32r2 and mips64r2 are NanLegacy-only since Nan2008
+  // was first introduced in Release 3. However, other compilers have
+  // traditionally allowed it for Release 2 so we should do the same.
   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("mips32r2", NanLegacy | Nan2008)
       .Case("mips32r3", NanLegacy | Nan2008)
       .Case("mips32r5", NanLegacy | Nan2008)
       .Case("mips32r6", Nan2008)
       .Case("mips64", NanLegacy)
-      .Case("mips64r2", NanLegacy)
+      .Case("mips64r2", NanLegacy | Nan2008)
       .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);

test/CodeGen/mips-unsupported-nan.c

-// 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
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips2 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NANLEGACY %s
+// RUN: FileCheck -check-prefix=CHECK-MIPS2 %s < %t
+//
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips3 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NANLEGACY %s
+// RUN: FileCheck -check-prefix=CHECK-MIPS3 %s < %t
+//
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips4 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NANLEGACY %s
+// RUN: FileCheck -check-prefix=CHECK-MIPS4 %s < %t
+//
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips32 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NANLEGACY %s
+// RUN: FileCheck -check-prefix=CHECK-MIPS32 %s < %t
+//
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips32r2 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NAN2008 %s
+// RUN: FileCheck -allow-empty -check-prefix=NO-WARNINGS %s < %t
+//
+// RUN: %clang -target mipsel-unknown-linux -mnan=2008 -march=mips32r3 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NAN2008 %s
+// RUN: FileCheck -allow-empty -check-prefix=NO-WARNINGS %s < %t
+//
+// RUN: %clang -target mipsel-unknown-linux -mnan=legacy -march=mips32r6 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NAN2008 %s
+// RUN: FileCheck -check-prefix=CHECK-MIPS32R6 %s < %t
+//
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips64 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NANLEGACY %s
+// RUN: FileCheck -check-prefix=CHECK-MIPS64 %s < %t
+//
+// RUN: %clang -target mips64el-unknown-linux -mnan=2008 -march=mips64r2 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NAN2008 %s
+// RUN: FileCheck -allow-empty -check-prefix=NO-WARNINGS %s < %t
+//
+// RUN: %clang -target mips64el-unknown-linux -mnan=legacy -march=mips64r6 -emit-llvm -S %s -o - 2>%t | FileCheck -check-prefix=CHECK-NAN2008 %s
+// RUN: FileCheck -check-prefix=CHECK-MIPS64R6 %s < %t
+
+// NO-WARNINGS-NOT: warning: ignoring '-mnan=legacy' option
+// NO-WARNINGS-NOT: warning: ignoring '-mnan=2008' option
 
 // 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("");