Add support for WritableRegister policy in the register allocator.

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.h"
@@ skipping 828 matching lines @@
       //                 j' i  i'
       //      value    --*
       //      register   [-----)
       //
       MoveOperands* move =
           AddMoveAt(pos - 1, *in_ref, Location::Any());
       BlockLocation(*in_ref, pos - 1, pos + 1);
       range->AddUseInterval(block->start_pos(), pos - 1);
       range->AddHintedUse(pos - 1, move->src_slot(), in_ref);
     } else if (in_ref->IsUnallocated()) {
-      // Normal unallocated input. Expected shape of
-      // live ranges:
-      //
-      //                 i  i'
-      //      value    -----*
-      //
-      ASSERT(in_ref->IsUnallocated());
-      range->AddUseInterval(block->start_pos(), pos + 1);
-      range->AddUse(pos + 1, in_ref);
+      if (in_ref->policy() == Location::kWritableRegister) {
+        // Writable unallocated input. Expected shape of
+        // live ranges:
+        //
+        //                 i  i'
+        //      value    --*
+        //      temp       [--)
+        MoveOperands* move = AddMoveAt(pos,
+                                       Location::RequiresRegister(),
+                                       Location::PrefersRegister());
+
+        // Add uses to the live range of the input.
+        range->AddUseInterval(block->start_pos(), pos);
+        range->AddUse(pos, move->src_slot());
+
+        // Create live range for the temporary.
+        LiveRange* temp = MakeLiveRangeForTemporary();
+        temp->AddUseInterval(pos, pos + 1);
+        temp->AddHintedUse(pos, in_ref, move->src_slot());
+        temp->AddUse(pos, move->dest_slot());
+        *in_ref = Location::RequiresRegister();
+        CompleteRange(temp, RegisterKindFromPolicy(*in_ref));
+      } else {
+        // Normal unallocated input. Expected shape of
+        // live ranges:
+        //
+        //                 i  i'
+        //      value    -----*
+        //
+        range->AddUseInterval(block->start_pos(), pos + 1);
+        range->AddUse(pos + 1, in_ref);
+      }
     } else {
       ASSERT(in_ref->IsConstant());
     }
   }
 
   // Process temps.
   for (intptr_t j = 0; j < locs->temp_count(); j++) {
     // Expected shape of live range:
     //
     //              i  i'
@@ skipping 1315 matching lines @@
     OS::Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(flow_graph_, true);
     printer.PrintBlocks();
     OS::Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart