tblgen: Use semantically correct RTTI functions.

Also, some minor cleanup.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165647 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/InstrInfoEmitter.cpp b/utils/TableGen/InstrInfoEmitter.cpp
index 34e363d..4e97cf4 100644
--- a/utils/TableGen/InstrInfoEmitter.cpp
+++ b/utils/TableGen/InstrInfoEmitter.cpp
@@ -89,7 +89,7 @@
       for (unsigned j = 0, e = Inst.Operands[i].MINumOperands; j != e; ++j) {
         OperandList.push_back(Inst.Operands[i]);
 
-        Record *OpR = dyn_cast<DefInit>(MIOI->getArg(j))->getDef();
+        Record *OpR = cast<DefInit>(MIOI->getArg(j))->getDef();
         OperandList.back().Rec = OpR;
       }
     }