Uses assembler macro for dart SP setup on arm64.

runtime/vm/assembler_arm64.h

 // 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.
 
 #ifndef VM_ASSEMBLER_ARM64_H_
 #define VM_ASSEMBLER_ARM64_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_arm64.h directly; use assembler.h instead.
 #endif
@@ skipping 1156 matching lines @@
   void CompareObject(Register reg, const Object& object, Register pp);
 
   void LoadClassId(Register result, Register object, Register pp);
   void LoadClassById(Register result, Register class_id, Register pp);
   void LoadClass(Register result, Register object, Register pp);
   void CompareClassId(Register object, intptr_t class_id, Register pp);
 
   void EnterFrame(intptr_t frame_size);
   void LeaveFrame();
 
+  // When entering Dart code from C++, we copy the system stack pointer (CSP)
+  // to the Dart stack pointer (SP), and reserve a little space for the stack
+  // to grow.
+  void SetupDartSP(intptr_t reserved_space) {
+    ASSERT(Utils::IsAligned(reserved_space, 16));
+    mov(SP, CSP);
+    sub(CSP, CSP, Operand(reserved_space));
+  }
+
   void EnterDartFrame(intptr_t frame_size);
   void EnterDartFrameWithInfo(intptr_t frame_size, Register new_pp);
   void EnterOsrFrame(intptr_t extra_size, Register new_pp);
   void LeaveDartFrame();
 
   void EnterCallRuntimeFrame(intptr_t frame_size);
   void LeaveCallRuntimeFrame();
   void CallRuntime(const RuntimeEntry& entry, intptr_t argument_count);
 
   // Set up a stub frame so that the stack traversal code can easily identify
@@ skipping 473 matching lines @@
                                   Register value,
                                   Label* no_update);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_ARM64_H_