[TableGen] Use 'isa' to identify UnsetInits rather than comparing with the singleton object created by UnsetInit::get(). Makes it more consistent with the other types.

llvm-svn: 235465
diff --git a/llvm/lib/TableGen/Record.cpp b/llvm/lib/TableGen/Record.cpp
index 3374432..29217d7 100644
--- a/llvm/lib/TableGen/Record.cpp
+++ b/llvm/lib/TableGen/Record.cpp
@@ -517,7 +517,7 @@
 // bits initializer will resolve into VarBitInit to keep the field name and bit
 // number used in targets with fixed insn length.
 static Init *fixBitInit(const RecordVal *RV, Init *Before, Init *After) {
-  if (RV || After != UnsetInit::get())
+  if (RV || !isa<UnsetInit>(After))
     return After;
   return Before;
 }
@@ -1961,7 +1961,7 @@
     PrintFatalError(getLoc(), "Record `" + getName() +
       "' does not have a field named `" + FieldName.str() + "'!\n");
 
-  if (R->getValue() == UnsetInit::get()) {
+  if (isa<UnsetInit>(R->getValue())) {
     Unset = true;
     return false;
   }