Change the baseline compiler to match the Hydrogen graph builder.

src/x64/full-codegen-x64.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 3096 matching lines @@
 
     case Token::VOID: {
       Comment cmnt(masm_, "[ UnaryOperation (VOID)");
       VisitForEffect(expr->expression());
       context()->Plug(Heap::kUndefinedValueRootIndex);
       break;
     }
 
     case Token::NOT: {
       Comment cmnt(masm_, "[ UnaryOperation (NOT)");
-      Label materialize_true, materialize_false;
-      Label* if_true = NULL;
-      Label* if_false = NULL;
-      Label* fall_through = NULL;
-      // Notice that the labels are swapped.
-      context()->PrepareTest(&materialize_true, &materialize_false,
-                             &if_false, &if_true, &fall_through);
-      if (context()->IsTest()) ForwardBailoutToChild(expr);
-      VisitForControl(expr->expression(), if_true, if_false, fall_through);
-      context()->Plug(if_false, if_true);  // Labels swapped.
+      if (context()->IsEffect()) {
+        // Unary NOT has no side effects so it's only necessary to visit the
+        // subexpression.  Match the optimizing compiler by not branching.
+        VisitForEffect(expr->expression());
+      } else {
+        Label materialize_true, materialize_false;
+        Label* if_true = NULL;
+        Label* if_false = NULL;
+        Label* fall_through = NULL;
+        // Notice that the labels are swapped.
+        context()->PrepareTest(&materialize_true, &materialize_false,
+                               &if_false, &if_true, &fall_through);
+        if (context()->IsTest()) ForwardBailoutToChild(expr);
+        VisitForControl(expr->expression(), if_true, if_false, fall_through);
+        context()->Plug(if_false, if_true);  // Labels swapped.
+      }
       break;
     }
 
     case Token::TYPEOF: {
       Comment cmnt(masm_, "[ UnaryOperation (TYPEOF)");
       { StackValueContext context(this);
         VisitForTypeofValue(expr->expression());
       }
       __ CallRuntime(Runtime::kTypeof, 1);
       context()->Plug(rax);
@@ skipping 625 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64