Save a few register moves in function prolog on arm64 by using the same pattern

runtime/vm/intermediate_language_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"  // Needed here to get TARGET_ARCH_ARM64.
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 85 matching lines @@
   __ Comment("Stack Check");
   const intptr_t fp_sp_dist =
       (kFirstLocalSlotFromFp + 1 - compiler->StackSize()) * kWordSize;
   ASSERT(fp_sp_dist <= 0);
   __ sub(R2, SP, Operand(FP));
   __ CompareImmediate(R2, fp_sp_dist);
   __ b(&stack_ok, EQ);
   __ brk(0);
   __ Bind(&stack_ok);
 #endif
+  ASSERT(__ constant_pool_allowed());
   __ LeaveDartFrame();  // Disallows constant pool use.
   __ ret();
   // This ReturnInstr may be emitted out of order by the optimizer. The next
   // block may be a target expecting a properly set constant pool pointer.
   __ set_constant_pool_allowed(true);
 }
 
 
 static Condition NegateCondition(Condition condition) {
   switch (condition) {
@@ skipping 5494 matching lines @@
                                 1,
                                 locs());
   __ Drop(1);
   __ Pop(result);
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64