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/FixedLenDecoderEmitter.cpp b/utils/TableGen/FixedLenDecoderEmitter.cpp
index aa4dd8a..c53776b 100644
--- a/utils/TableGen/FixedLenDecoderEmitter.cpp
+++ b/utils/TableGen/FixedLenDecoderEmitter.cpp
@@ -1757,8 +1757,8 @@
     // for decoding register classes.
     // FIXME: This need to be extended to handle instructions with custom
     // decoder methods, and operands with (simple) MIOperandInfo's.
-    TypedInit *TI = dyn_cast<TypedInit>(NI->first);
-    RecordRecTy *Type = dyn_cast<RecordRecTy>(TI->getType());
+    TypedInit *TI = cast<TypedInit>(NI->first);
+    RecordRecTy *Type = cast<RecordRecTy>(TI->getType());
     Record *TypeRecord = Type->getRecord();
     bool isReg = false;
     if (TypeRecord->isSubClassOf("RegisterOperand"))