Ignore life ranges with no uses for a values defined as fixed output.

runtime/vm/flow_graph_allocator.cc

 // Copyright (c) 2012, 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_builder.h"
@@ skipping 737 matching lines @@
     //    output             [-------
     //
     BlockLocation(*out, pos, pos + 1);
 
     if (range->vreg() == kTempVirtualRegister) return;
 
     // We need to emit move connecting fixed register with another location
     // that will be allocated for this output's live range.
     // Special case: fixed output followed by a fixed input last use.
     UsePosition* use = range->first_use();
+
+    // If the value has no uses we don't need to allocate it.
+    if (use == NULL) return;
+
     if (use->pos() == (pos + 1)) {
       // We have a use position on the parallel move.
       ASSERT(use->location_slot()->IsUnallocated());
       *(use->location_slot()) = *out;
 
       // Remove first use. It was allocated.
       range->set_first_use(range->first_use()->next());
     }
 
     // Shorten live range to the point of definition, this might make the range
@@ skipping 880 matching lines @@
 
   if (FLAG_trace_ssa_allocator) {
     OS::Print("-- ir after allocation -------------------------\n");
     FlowGraphPrinter printer(Function::Handle(), block_order_, true);
     printer.PrintBlocks();
   }
 }
 
 
 }  // namespace dart