[crankshaft] For-in index increment cannot overflow.

src/crankshaft/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/crankshaft/hydrogen.h"
 
 #include <sstream>
 
 #include "src/allocation-site-scopes.h"
 #include "src/ast/ast-numbering.h"
@@ skipping 5426 matching lines @@
     CHECK_BAILOUT(VisitLoopBody(stmt, loop_entry));
   }
 
   HBasicBlock* body_exit =
       JoinContinue(stmt, current_block(), break_info.continue_block());
 
   if (body_exit != NULL) {
     set_current_block(body_exit);
 
     HValue* current_index = Pop();
-    Push(AddUncasted<HAdd>(current_index, graph()->GetConstant1()));
+    HValue* increment =
+        AddUncasted<HAdd>(current_index, graph()->GetConstant1());
+    increment->ClearFlag(HValue::kCanOverflow);
+    Push(increment);
     body_exit = current_block();
   }
 
   HBasicBlock* loop_exit = CreateLoop(stmt,
                                       loop_entry,
                                       body_exit,
                                       loop_successor,
                                       break_info.break_block());
 
   set_current_block(loop_exit);
@@ skipping 8154 matching lines @@
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8