Clean some unuse code of unary negation

src/ast.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 289 matching lines @@
   // information. However the GraphBuilder expects it to be on the instruction
   // corresponding to the TestContext, therefore we have to store it here and
   // not on the operand.
   set_to_boolean_types(oracle->ToBooleanTypes(expression()->test_id()));
 }
 
 
 bool UnaryOperation::ResultOverwriteAllowed() {
   switch (op_) {
     case Token::BIT_NOT:
-    case Token::SUB:
       return true;
     default:
       return false;
   }
 }
 
 
 void BinaryOperation::RecordToBooleanTypeFeedback(TypeFeedbackOracle* oracle) {
   // TODO(olivf) If this Operation is used in a test context, then the right
   // hand side has a ToBoolean stub and we want to collect the type information.
@@ skipping 879 matching lines @@
     OS::SNPrintF(buffer, "%d", Smi::cast(*value_)->value());
     str = arr;
   } else {
     str = DoubleToCString(value_->Number(), buffer);
   }
   return factory->NewStringFromAscii(CStrVector(str));
 }
 
 
 } }  // namespace v8::internal