When canonicalizing UnboxInt32([tr], BoxInt64()) make sure to mark resulting converter truncating.

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 1190 matching lines @@
   const intptr_t value_cid = value()->Type()->ToCid();
   if (value_cid == kSmiCid) {
     return (kSmiBits > 32) &&
         !is_truncating() &&
         !RangeUtils::Fits(value()->definition()->range(),
                           RangeBoundary::kRangeBoundaryInt32);
   } else if (value_cid == kMintCid) {
     return !is_truncating() &&
         !RangeUtils::Fits(value()->definition()->range(),
                           RangeBoundary::kRangeBoundaryInt32);
+  } else if (is_truncating() && value()->definition()->IsBoxInteger()) {
+    return false;
   } else if ((kSmiBits < 32) && value()->Type()->IsInt()) {
     // Note: we don't support truncation of Bigint values.
     return !RangeUtils::Fits(value()->definition()->range(),
                              RangeBoundary::kRangeBoundaryInt32);
   } else {
     return true;
   }
 }
 
 
@@ skipping 835 matching lines @@
   if (box_defn != NULL) {
     if (box_defn->value()->definition()->representation() == representation()) {
       return box_defn->value()->definition();
     } else {
       UnboxedIntConverterInstr* converter = new UnboxedIntConverterInstr(
           box_defn->value()->definition()->representation(),
           representation(),
           box_defn->value()->CopyWithType(),
           (representation() == kUnboxedInt32) ?
               GetDeoptId() : Isolate::kNoDeoptId);
-      if ((representation() == kUnboxedInt32) && !CanDeoptimize()) {
+      if ((representation() == kUnboxedInt32) && is_truncating()) {
         converter->mark_truncating();
       }
       flow_graph->InsertBefore(this, converter, env(), FlowGraph::kValue);
       return converter;
     }
   }
 
   return this;
 }
 
@@ skipping 1393 matching lines @@
     case Token::kTRUNCDIV: return 0;
     case Token::kMOD: return 1;
     default: UNIMPLEMENTED(); return -1;
   }
 }
 
 
 #undef __
 
 }  // namespace dart