Don't mark register constraints resolution moves as prefering registers.

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 683 matching lines @@
 
     if (in_ref->IsRegister()) {
       // Input is expected in a fixed register. Expected shape of
       // live ranges:
       //
       //                 j' i  i'
       //      value    --*
       //      register   [-----)
       //
       MoveOperands* move =
-          AddMoveAt(pos - 1, *in_ref, Location::PrefersRegister());
+          AddMoveAt(pos - 1, *in_ref, Location::Any());
       BlockLocation(*in_ref, pos - 1, pos + 1);
       range->AddUseInterval(block->start_pos(), pos - 1);
       range->AddUse(pos - 1, move->src_slot());
     } else {
       // Normal unallocated input. Expected shape of
       // live ranges:
       //
       //                 i  i'
       //      value    -----*
       //
@@ skipping 99 matching lines @@
       // 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
     // empty (if the only use immediately follows). If range is not empty add
     // move from a fixed register to an unallocated location.
     range->DefineAt(pos + 1);
     if (range->Start() == range->End()) return;
 
-    MoveOperands* move = AddMoveAt(pos + 1, Location::PrefersRegister(), *out);
+    MoveOperands* move = AddMoveAt(pos + 1, Location::Any(), *out);
     range->AddUse(pos + 1, move->dest_slot());
   } else if (output_same_as_first_input) {
     // Output register will contain a value of the first input at instruction's
     // start. Expected shape of live ranges:
     //
     //                 i  i'
     //    input #0   --*
     //    output       [----
     //
     ASSERT(locs->in_slot(0)->Equals(Location::RequiresRegister()));
 
     // Create move that will copy value between input and output.
     locs->set_out(Location::RequiresRegister());
     MoveOperands* move = AddMoveAt(pos,
                                    Location::RequiresRegister(),
-                                   Location::PrefersRegister());
+                                   Location::Any());
 
     // Add uses to the live range of the input.
     Value* input = current->InputAt(0);
     ASSERT(input->IsUse());  // Can not be a constant currently.
     LiveRange* input_range = GetLiveRange(
       input->AsUse()->definition()->ssa_temp_index());
     input_range->AddUseInterval(block->start_pos(), pos);
     input_range->AddUse(pos, move->src_slot());
 
     // Shorten output live range to the point of definition and add both input
@@ skipping 1031 matching lines @@
     OS::Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(Function::Handle(), block_order_, true);
     printer.PrintBlocks();
     OS::Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart