Add support for WritableRegister policy in the register allocator.

runtime/vm/flow_graph_compiler.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/globals.h"  // Needed here to get TARGET_ARCH_XXX.
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
@@ skipping 637 matching lines @@
   }
 
   // Allocate all unallocated input locations.
   const bool should_pop = !instr->IsPushArgument();
   for (intptr_t i = locs->input_count() - 1; i >= 0; i--) {
     Location loc = locs->in(i);
     Register reg = kNoRegister;
     if (loc.IsRegister()) {
       reg = loc.reg();
     } else if (loc.IsUnallocated()) {
-      ASSERT(loc.policy() == Location::kRequiresRegister);
+      ASSERT((loc.policy() == Location::kRequiresRegister) ||
+             (loc.policy() == Location::kWritableRegister));
       reg = AllocateFreeRegister(blocked_registers);
       locs->set_in(i, Location::RegisterLocation(reg));
     }
 
     // Inputs are consumed from the simulated frame. In case of a call argument
     // we leave it until the call instruction.
     if (should_pop) {
       assembler()->PopRegister(reg);
     }
   }
 
   // Allocate all unallocated temp locations.
   for (intptr_t i = 0; i < locs->temp_count(); i++) {
     Location loc = locs->temp(i);
     if (loc.IsUnallocated()) {
       ASSERT(loc.policy() == Location::kRequiresRegister);
       loc = Location::RegisterLocation(
         AllocateFreeRegister(blocked_registers));
       locs->set_temp(i, loc);
     }
   }
 
   Location result_location = locs->out();
   if (result_location.IsUnallocated()) {
     switch (result_location.policy()) {
       case Location::kAny:
       case Location::kPrefersRegister:
       case Location::kRequiresRegister:
+      case Location::kWritableRegister:
         result_location = Location::RegisterLocation(
             AllocateFreeRegister(blocked_registers));
         break;
       case Location::kSameAsFirstInput:
         result_location = locs->in(0);
         break;
       case Location::kRequiresXmmRegister:
         UNREACHABLE();
         break;
     }
@@ skipping 146 matching lines @@
     case ABOVE:         return unsigned_left > unsigned_right;
     case ABOVE_EQUAL:   return unsigned_left >= unsigned_right;
     default:
       UNIMPLEMENTED();
       return false;
   }
 }
 
 
 }  // namespace dart