Change environment padding value to value with smi representation.

src/hydrogen.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 1032 matching lines @@
     current_block()->Goto(continuation);
   }
 }
 
 
 void HGraphBuilder::PadEnvironmentForContinuation(
     HBasicBlock* from,
     HBasicBlock* continuation) {
   if (continuation->last_environment() != NULL) {
     // When merging from a deopt block to a continuation, resolve differences in
-    // environment by pushing undefined and popping extra values so that the
-    // environments match during the join.
+    // environment by pushing constant 0 and popping extra values so that the
+    // environments match during the join. Push 0 since it has the most specific
+    // representation, and will not influence representation inference of the
+    // phi.
     int continuation_env_length = continuation->last_environment()->length();
     while (continuation_env_length != from->last_environment()->length()) {
       if (continuation_env_length > from->last_environment()->length()) {
-        from->last_environment()->Push(graph()->GetConstantUndefined());
+        from->last_environment()->Push(graph()->GetConstant0());
       } else {
         from->last_environment()->Pop();
       }
     }
   } else {
     ASSERT(continuation->predecessors()->length() == 0);
   }
 }
 
 
@@ skipping 8658 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal