Reland and fix bug: Don't store redundant compile-type at values.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
@@ skipping 2033 matching lines @@
     } else {
       UnboxedIntConverterInstr* converter = new UnboxedIntConverterInstr(
           box_defn->value()->definition()->representation(),
           representation(),
           box_defn->value()->CopyWithType(),
           (representation() == kUnboxedInt32) ?
               GetDeoptId() : Isolate::kNoDeoptId);
       if ((representation() == kUnboxedInt32) && !CanDeoptimize()) {
         converter->mark_truncating();
       }
-      flow_graph->InsertBefore(this, converter, env(), FlowGraph::kValue);
-      return converter;
+      // Only replace if the replacement has CanDeoptimize is consistent with
+      // the original instructions. We may have removed environments already.
+      // Due to the way type propagation works currently, the CompileType of the
+      // converter input may not be the same (more general) than the information
+      // about the input of this unboxing instructions.
+      if (CanDeoptimize() == converter->CanDeoptimize()) {
+        flow_graph->InsertBefore(this, converter, env(), FlowGraph::kValue);
+        return converter;
+      }
     }
   }
 
   return this;
 }
 
 
 Definition* UnboxInt32Instr::Canonicalize(FlowGraph* flow_graph) {
   Definition* replacement = UnboxIntegerInstr::Canonicalize(flow_graph);
   if (replacement != this) {
@@ skipping 1303 matching lines @@
     case Token::kTRUNCDIV: return 0;
     case Token::kMOD: return 1;
     default: UNIMPLEMENTED(); return -1;
   }
 }
 
 
 #undef __
 
 }  // namespace dart