[tblgen] Fix behavior of !isa to prevent premature folding

llvm/lib/TableGen/Record.cpp

@@ -2094,10 +2094,12 @@ const Init *IsAOpInit::Fold() const {
       return IntInit::get(getRecordKeeper(), 1);
 
     if (isa<RecordRecTy>(CheckType)) {
-      // If the target type is not a subclass of the expression type, or if
-      // the expression has fully resolved to a record, we know that it can't
-      // be of the required type.
-      if (!CheckType->typeIsConvertibleTo(TI->getType()) || isa<DefInit>(Expr))
+      // If the target type is not a subclass of the expression type once the
+      // expression has been made concrete, or if the expression has fully
+      // resolved to a record, we know that it can't be of the required type.
+      if ((!CheckType->typeIsConvertibleTo(TI->getType()) &&
+           Expr->isConcrete()) ||
+          isa<DefInit>(Expr))
         return IntInit::get(getRecordKeeper(), 0);
     } else {
       // We treat non-record types as not castable.

llvm/test/TableGen/isa-non-primary.td

@@ -0,0 +1,33 @@
+// RUN: llvm-tblgen %s | FileCheck %s
+
+// CHECK: --- Defs ---
+// CHECK: def Op1 {       // Op
+// CHECK-NEXT:  string res = "yes";
+// CHECK-NEXT: }
+// CHECK: def Op2 {       // Op
+// CHECK-NEXT:  string res = "no";
+// CHECK-NEXT: }
+
+class A<int a> {
+  int x = a;
+}
+
+class B<int a> : A<a> {
+  bit y = 0;
+}
+
+class C<int a> {
+  int z = !add(a, 16);
+}
+
+class D<int a> : B<a>, C<a>;
+
+def E1 : D<5>;
+def E2 : B<2>;
+
+class Op<A value> {
+  string res = !if(!isa<C>(value), "yes", "no");
+}
+
+def Op1 : Op<E1>;
+def Op2 : Op<E2>;