Fix the semantics of delete on parameters.

src/hydrogen.cc

 // Copyright 2011 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 4635 matching lines @@
       VISIT_FOR_EFFECT(expr->expression());
       ast_context()->ReturnValue(graph()->GetConstantTrue());
     } else if (var != NULL &&
                !var->is_global() &&
                var->AsSlot() != NULL &&
                var->AsSlot()->type() != Slot::LOOKUP) {
       // Result of deleting non-global, non-dynamic variables is false.
       // The subexpression does not have side effects.
       ast_context()->ReturnValue(graph()->GetConstantFalse());
     } else if (prop != NULL) {
-      VISIT_FOR_VALUE(prop->obj());
-      VISIT_FOR_VALUE(prop->key());
-      HValue* key = Pop();
-      HValue* obj = Pop();
-      ast_context()->ReturnInstruction(new HDeleteProperty(obj, key),
-                                       expr->id());
+      if (prop->is_synthetic()) {
+        // Result of deleting parameters is false, even when they rewrite
+        // to accesses on the arguments object.
+        ast_context()->ReturnValue(graph()->GetConstantFalse());
+      } else {
+        VISIT_FOR_VALUE(prop->obj());
+        VISIT_FOR_VALUE(prop->key());
+        HValue* key = Pop();
+        HValue* obj = Pop();
+        HDeleteProperty* instr = new HDeleteProperty(obj, key);
+        ast_context()->ReturnInstruction(instr, expr->id());
+      }
     } else if (var->is_global()) {
       BAILOUT("delete with global variable");
     } else {
       BAILOUT("delete with non-global variable");
     }
   } else if (op == Token::NOT) {
     if (ast_context()->IsTest()) {
       TestContext* context = TestContext::cast(ast_context());
       VisitForControl(expr->expression(),
                       context->if_false(),
@@ skipping 1334 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal