Fix assertion on !eq(?, 0)

Instead of asserting, emit a proper error message

llvm/lib/TableGen/TGParser.cpp

@@ -1180,7 +1180,13 @@ Init *TGParser::ParseOperation(Record *CurRec, RecTy *ItemType) {
       InitList.push_back(ParseValue(CurRec, ArgType));
       if (!InitList.back()) return nullptr;
 
-      RecTy *ListType = cast<TypedInit>(InitList.back())->getType();
+      TypedInit *InitListBack = dyn_cast<TypedInit>(InitList.back());
+      if (!InitListBack) {
+        Error(OpLoc, Twine("expected value to be a typed value, got '" +
+                           InitList.back()->getAsString() + "'"));
+        return nullptr;
+      }
+      RecTy *ListType = InitListBack->getType();
       if (!ArgType) {
         ArgType = ListType;
 

llvm/test/TableGen/eq-unset.td

@@ -0,0 +1,9 @@
+// RUN: not llvm-tblgen %s 2>&1 | FileCheck %s
+
+// CHECK: error: expected value to be a typed value, got '?'
+
+def Z1 {
+  // This one caused an assertion because the value was an UnsetInit
+  // and !eq() can only accept TypedInit's.
+  bit D = !if(!eq(?, 0), 1, 0);
+}