Free one bit in Map by removing unused retaining counter.

src/arm64/builtins-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/arm64/frames-arm64.h"
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
@@ skipping 409 matching lines @@
         __ LoadRoot(filler, Heap::kUndefinedValueRootIndex);
 
         if (!is_api_function) {
           Label no_inobject_slack_tracking;
 
           Register constructon_count = x14;
           MemOperand bit_field3 =
               FieldMemOperand(init_map, Map::kBitField3Offset);
           // Check if slack tracking is enabled.
           __ Ldr(x11, bit_field3);
-          __ DecodeField<Map::Counter>(constructon_count, x11);
+          __ DecodeField<Map::ConstructionCounter>(constructon_count, x11);
           __ Cmp(constructon_count, Operand(Map::kSlackTrackingCounterEnd));
           __ B(lt, &no_inobject_slack_tracking);
           // Decrease generous allocation count.
-          __ Subs(x11, x11, Operand(1 << Map::Counter::kShift));
+          __ Subs(x11, x11, Operand(1 << Map::ConstructionCounter::kShift));
           __ Str(x11, bit_field3);
 
           // Allocate object with a slack.
           Register unused_props = x11;
           __ Ldr(unused_props,
                  FieldMemOperand(init_map, Map::kInstanceAttributesOffset));
           __ Ubfx(unused_props, unused_props,
                   Map::kUnusedPropertyFieldsByte * kBitsPerByte, kBitsPerByte);
 
           Register end_of_pre_allocated = x11;
@@ skipping 1577 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM