In the absence of type feedback, pessimistically force Tagged representation for UnaryAdd

src/hydrogen.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 8595 matching lines @@
   return ast_context()->ReturnInstruction(instr, expr->id());
 }
 
 
 void HOptimizedGraphBuilder::VisitAdd(UnaryOperation* expr) {
   CHECK_ALIVE(VisitForValue(expr->expression()));
   HValue* value = Pop();
   HValue* context = environment()->LookupContext();
   HInstruction* instr =
       HMul::New(zone(), context, value, graph()->GetConstant1());
+  if (instr->IsBinaryOperation()) {
+    // Since we don't have type feedback, we must be cautious/pessimistic.
+    HBinaryOperation::cast(instr)->set_observed_input_representation(
+        Representation::Tagged(), Representation::Tagged());
+  }
   return ast_context()->ReturnInstruction(instr, expr->id());
 }
 
 
 void HOptimizedGraphBuilder::VisitSub(UnaryOperation* expr) {
   CHECK_ALIVE(VisitForValue(expr->expression()));
   HValue* value = Pop();
   HValue* context = environment()->LookupContext();
   HInstruction* instr =
       HMul::New(zone(), context, value, graph()->GetConstantMinus1());
@@ skipping 2168 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal