diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index dfff2099cbd6..c8d4e2b2b6ea 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -971,6 +971,8 @@ bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
   case Builtin::BI__builtin_object_size: {
     const Expr *Arg = E->getArg(0)->IgnoreParens();
     Expr::EvalResult Base;
+    
+    // TODO: Perhaps we should let LLVM lower this?
     if (Arg->EvaluateAsAny(Base, Info.Ctx)
         && Base.Val.getKind() == APValue::LValue
         && !Base.HasSideEffects)
@@ -992,7 +994,8 @@ bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
           }
         }
 
-    // TODO: Perhaps we should let LLVM lower this?
+    // If evaluating the argument has side-effects we can't determine
+    // the size of the object and lower it to unknown now.
     if (E->getArg(0)->HasSideEffects(Info.Ctx)) {
       if (E->getArg(1)->EvaluateAsInt(Info.Ctx).getZExtValue() <= 1)
         return Success(-1ULL, E);