Index: include/clang/Basic/LangOptions.def
===================================================================
--- include/clang/Basic/LangOptions.def	(revision 146622)
+++ include/clang/Basic/LangOptions.def	(working copy)
@@ -121,6 +121,7 @@
 BENIGN_LANGOPT(InlineVisibilityHidden , 1, 0, "hidden default visibility for inline C++ methods")
 BENIGN_LANGOPT(ParseUnknownAnytype, 1, 0, "__unknown_anytype")
 BENIGN_LANGOPT(DebuggerSupport , 1, 0, "debugger support")
+BENIGN_LANGOPT(DebuggerCastResultToId, 1, 0, "for 'po' in the debugger, cast the result to id if it is of unknown type")
 BENIGN_LANGOPT(AddressSanitizer , 1, 0, "AddressSanitizer enabled")
 
 BENIGN_LANGOPT(SpellChecking , 1, 1, "spell-checking")
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp	(revision 146622)
+++ lib/Sema/SemaExprCXX.cpp	(working copy)
@@ -4675,7 +4675,7 @@
     return ExprError();
 
   // Top-level message sends default to 'id' when we're in a debugger.
-  if (getLangOptions().DebuggerSupport &&
+  if (getLangOptions().DebuggerCastResultToId &&
       FullExpr.get()->getType() == Context.UnknownAnyTy &&
       isa<ObjCMessageExpr>(FullExpr.get())) {
     FullExpr = forceUnknownAnyToType(FullExpr.take(), Context.getObjCIdType());