More compact string representation on 64 bit.

runtime/vm/assembler_arm64.cc

 // Copyright (c) 2014, 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"  // NOLINT
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/longjump.h"
@@ skipping 955 matching lines @@
   if (Address::CanHoldOffset(offset - kHeapObjectTag)) {
     StoreIntoObjectNoBarrier(object, FieldAddress(object, offset), value);
   } else {
     AddImmediate(TMP, object, offset - kHeapObjectTag);
     StoreIntoObjectNoBarrier(object, Address(TMP), value);
   }
 }
 
 
 void Assembler::LoadClassId(Register result, Register object) {
-  ASSERT(RawObject::kClassIdTagPos == kBitsPerInt32);
-  ASSERT(RawObject::kClassIdTagSize == kBitsPerInt32);
+  ASSERT(RawObject::kClassIdTagPos == 16);
+  ASSERT(RawObject::kClassIdTagSize == 16);
   const intptr_t class_id_offset =
       Object::tags_offset() + RawObject::kClassIdTagPos / kBitsPerByte;
   LoadFromOffset(result, object, class_id_offset - kHeapObjectTag,
-                 kUnsignedWord);
+                 kUnsignedHalfword);
 }
 
 
 void Assembler::LoadClassById(Register result, Register class_id) {
   ASSERT(result != class_id);
   LoadIsolate(result);
   const intptr_t offset =
       Isolate::class_table_offset() + ClassTable::table_offset();
   LoadFromOffset(result, result, offset);
   ldr(result, Address(result, class_id, UXTX, Address::Scaled));
@@ skipping 579 matching lines @@
   str(tmp, Address(addr, 7), kUnsignedByte);
   if (sz == kDoubleWord) {
     return;
   }
   UNIMPLEMENTED();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64