Ignore definitions without uses in FlowGraphAllocator::CollectRepresentations.

runtime/vm/flow_graph_allocator.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/flow_graph_allocator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/intermediate_language.h"
 #include "vm/il_printer.h"
 #include "vm/flow_graph.h"
@@ skipping 2414 matching lines @@
   mint_values_ = new BitVector(flow_graph_.max_virtual_register_number());
 
   for (BlockIterator it = flow_graph_.reverse_postorder_iterator();
        !it.Done();
        it.Advance()) {
     BlockEntryInstr* block = it.Current();
     // TODO(fschneider): Support unboxed mint representation for phis.
     for (ForwardInstructionIterator instr_it(block);
          !instr_it.Done();
          instr_it.Advance()) {
-      Instruction* instr = instr_it.Current();
-      if (instr->IsDefinition() && instr->representation() == kUnboxedMint) {
-        mint_values_->Add(instr->AsDefinition()->ssa_temp_index());
+      Definition* defn = instr_it.Current()->AsDefinition();
+      if ((defn != NULL) &&
+          (defn->ssa_temp_index() >= 0) &&
+          (defn->representation() == kUnboxedMint)) {
+        mint_values_->Add(defn->ssa_temp_index());
       }
     }
   }
 }
 
 
 void FlowGraphAllocator::AllocateRegisters() {
   CollectRepresentations();
 
   EliminateEnvironmentUses();
@@ skipping 61 matching lines @@
     OS::Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(flow_graph_, true);
     printer.PrintBlocks();
     OS::Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart