Prevent ARM Assembler crashing on unrecognised assembly format for DSB instruction


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159257 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index d375e35..830e9c0 100644
--- a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -3256,7 +3256,8 @@
 parseMemBarrierOptOperand(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
   SMLoc S = Parser.getTok().getLoc();
   const AsmToken &Tok = Parser.getTok();
-  assert(Tok.is(AsmToken::Identifier) && "Token is not an Identifier");
+  if (!Tok.is(AsmToken::Identifier))
+    return MatchOperand_NoMatch;
   StringRef OptStr = Tok.getString();
 
   unsigned Opt = StringSwitch<unsigned>(OptStr.slice(0, OptStr.size()))