Adds load/store from signed unscaled 9-bit offset w/ no writeback.

runtime/vm/simulator_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 <math.h>  // for isnan.
 #include <setjmp.h>
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
@@ skipping 1303 matching lines @@
   const int64_t rn_val = get_register(rn, R31IsSP);
   const uint32_t size = instr->SzField();
   uword address = 0;
   uword wb_address = 0;
   bool wb = false;
   if (instr->Bit(24) == 1) {
     // addr = rn + scaled unsigned 12-bit immediate offset.
     const uint32_t imm12 = static_cast<uint32_t>(instr->Imm12Field());
     const uint32_t offset = imm12 << size;
     address = rn_val + offset;
+  }  else if (instr->Bits(10, 2) == 0) {
+    // addr = rn + signed 9-bit immediate offset.
+    wb = false;
+    const int64_t offset = static_cast<int64_t>(instr->SImm9Field());
+    address = rn_val + offset;
+    wb_address = rn_val;
   } else if (instr->Bit(10) == 1) {
     // addr = rn + signed 9-bit immediate offset.
     wb = true;
     const int64_t offset = static_cast<int64_t>(instr->SImm9Field());
     if (instr->Bit(11) == 1) {
       // Pre-index.
       address = rn_val + offset;
       wb_address = address;
     } else {
       // Post-index.
@@ skipping 662 matching lines @@
   int64_t return_value;
   return_value = get_register(R0);
   return return_value;
 }
 
 }  // namespace dart
 
 #endif  // !defined(HOST_ARCH_ARM64)
 
 #endif  // defined TARGET_ARCH_ARM64