Allow HPhis to have an invalid merge index.

src/hydrogen-osr.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 99 matching lines @@
 
 void HOsrBuilder::FinishGraph() {
   // do nothing for now.
 }
 
 
 void HOsrBuilder::FinishOsrValues() {
   const ZoneList<HPhi*>* phis = osr_loop_entry_->phis();
   for (int j = 0; j < phis->length(); j++) {
     HPhi* phi = phis->at(j);
+    ASSERT(phi->HasMergedIndex());
     osr_values_->at(phi->merged_index())->set_incoming_value(phi);
   }
 }
 
 } }  // namespace v8::internal