diff --git a/llvm/include/llvm/Demangle/ItaniumDemangle.h b/llvm/include/llvm/Demangle/ItaniumDemangle.h
--- a/llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ b/llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -3885,6 +3885,18 @@
     // but the exception to that exception is vendor extended types (Itanium C++
     // ABI 5.9.1).
     Result = make<NameType>(Res);
+
+    // demangle builtin type transformations introduced in https://reviews.llvm.org/D116203
+    if (consumeIf('I')) {
+      Node *BaseType = parseType();
+      if (BaseType == nullptr)
+        return nullptr;
+      Result = make<FunctionEncoding>(nullptr, Result, makeNodeArray(&BaseType, &BaseType+1),
+                                      nullptr, Qualifiers::QualNone,
+                                      FunctionRefQual::FrefQualNone);
+      if (!consumeIf('E'))
+        return nullptr;
+    }
     break;
   }
   case 'D':