Change error handling to be consistent within each file

Author: Icohedron

llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp

@@ -322,10 +322,9 @@ static Value *expandIsFPClass(CallInst *Orig) {
     return RetVal;
   }
   default:
-    // Deliberately falling through to the unreachable below.
-    break;
+    report_fatal_error(Twine("Unsupported FPClassTest"),
+                       /* gen_crash_diag=*/false);
   }
-  llvm_unreachable("Unsupported FPClassTest");
 }
 
 static Value *expandAnyOrAllIntrinsic(CallInst *Orig,

llvm/lib/Target/DirectX/DXILOpLowering.cpp

@@ -766,7 +766,10 @@ class OpLowerer {
         OpCode = dxil::OpCode::IsFinite;
         break;
       default:
-        llvm_unreachable("Unsupported FPClassTest for DXILOpLowering");
+        SmallString<128> Msg =
+            formatv("Unsupported FPClassTest {0} for DXIL Op Lowering",
+                    TCI->getZExtValue());
+        return make_error<StringError>(Msg, inconvertibleErrorCode());
       }
 
       Expected<CallInst *> OpCall =