Don't propagate information through phis in loop headers.

src/hydrogen-check-elimination.cc

 // Copyright 2013 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 146 matching lines @@
       } else {
         // Leave it NULL till we meet a new check instruction for this object
         // in the control flow.
         new_entry->check_ = NULL;
       }
     }
     copy->cursor_ = cursor_;
     copy->size_ = size_;
 
     // Create entries for succ block's phis.
-    if (succ->phis()->length() > 0) {
+    if (!succ->IsLoopHeader() && succ->phis()->length() > 0) {
       int pred_index = succ->PredecessorIndexOf(from_block);
       for (int phi_index = 0;
            phi_index < succ->phis()->length();
            ++phi_index) {
         HPhi* phi = succ->phis()->at(phi_index);
         HValue* phi_operand = phi->OperandAt(pred_index);
 
         HCheckTableEntry* pred_entry = copy->Find(phi_operand);
         if (pred_entry != NULL) {
           // Create an entry for a phi in the table.
@@ skipping 523 matching lines @@
   PRINT_STAT(removed_cho);
   PRINT_STAT(narrowed);
   PRINT_STAT(loads);
   PRINT_STAT(empty);
   PRINT_STAT(compares_true);
   PRINT_STAT(compares_false);
   PRINT_STAT(transitions);
 }
 
 } }  // namespace v8::internal