r324433 - [NFC] Change odd cast-through-unknown behavior to an Optional

[Erich Keane via cfe-commits]

Author: erichkeane
Date: Tue Feb  6 16:37:19 2018
New Revision: 324433

URL: http://llvm.org/viewvc/llvm-project?rev=324433&view=rev
Log:
[NFC] Change odd cast-through-unknown behavior to an Optional

This bit of code in the driver uses '~0U' as a sentinel value.
The result is an odd mishmash of casts just to work.  This replaces
it with an optional,  which is a little less crazy looking.
--ehis line, and those below, will be ignored--

M    lib/Driver/Driver.cpp

Modified:
    cfe/trunk/lib/Driver/Driver.cpp

Modified: cfe/trunk/lib/Driver/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/Driver.cpp?rev=324433&r1=324432&r2=324433&view=diff
==============================================================================
--- cfe/trunk/lib/Driver/Driver.cpp (original)
+++ cfe/trunk/lib/Driver/Driver.cpp Tue Feb  6 16:37:19 2018
@@ -148,15 +148,15 @@ void Driver::setDriverModeFromOption(Str
     return;
   StringRef Value = Opt.drop_front(OptName.size());
 
-  const unsigned M = llvm::StringSwitch<unsigned>(Value)
-                         .Case("gcc", GCCMode)
-                         .Case("g++", GXXMode)
-                         .Case("cpp", CPPMode)
-                         .Case("cl", CLMode)
-                         .Default(~0U);
+  auto M = llvm::StringSwitch<llvm::Optional<DriverMode>>(Value)
+                           .Case("gcc", GCCMode)
+                           .Case("g++", GXXMode)
+                           .Case("cpp", CPPMode)
+                           .Case("cl", CLMode)
+                           .Default(None);
 
-  if (M != ~0U)
-    Mode = static_cast<DriverMode>(M);
+  if (M)
+    Mode = M.getValue();
   else
     Diag(diag::err_drv_unsupported_option_argument) << OptName << Value;
 }