Clean up some Release build warnings.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147289 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PTX/PTXMFInfoExtract.cpp b/lib/Target/PTX/PTXMFInfoExtract.cpp
index 26ec623..172a0e0 100644
--- a/lib/Target/PTX/PTXMFInfoExtract.cpp
+++ b/lib/Target/PTX/PTXMFInfoExtract.cpp
@@ -71,6 +71,8 @@
       RegType = PTXRegisterType::F32;
     else if (TRC == PTX::RegF64RegisterClass)
       RegType = PTXRegisterType::F64;
+    else
+      llvm_unreachable("Unkown register class.");
     MFI->addRegister(Reg, RegType, PTXRegisterSpace::Reg);
   }