Free one bit in Map by removing unused retaining counter.

src/arm/builtins-arm.cc

 // Copyright 2012 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_ARM
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 402 matching lines @@
         // r5: First in-object property of JSObject (not tagged)
         __ LoadRoot(r6, Heap::kUndefinedValueRootIndex);
 
         if (!is_api_function) {
           Label no_inobject_slack_tracking;
 
           // Check if slack tracking is enabled.
           MemOperand bit_field3 = FieldMemOperand(r2, Map::kBitField3Offset);
           // Check if slack tracking is enabled.
           __ ldr(r0, bit_field3);
-          __ DecodeField<Map::Counter>(ip, r0);
+          __ DecodeField<Map::ConstructionCounter>(ip, r0);
           // ip: slack tracking counter
           __ cmp(ip, Operand(Map::kSlackTrackingCounterEnd));
           __ b(lt, &no_inobject_slack_tracking);
           __ push(ip);  // Save allocation count value.
           // Decrease generous allocation count.
-          __ sub(r0, r0, Operand(1 << Map::Counter::kShift));
+          __ sub(r0, r0, Operand(1 << Map::ConstructionCounter::kShift));
           __ str(r0, bit_field3);
 
           // Allocate object with a slack.
           __ ldr(r0, FieldMemOperand(r2, Map::kInstanceAttributesOffset));
           __ Ubfx(r0, r0, Map::kUnusedPropertyFieldsByte * kBitsPerByte,
                   kBitsPerByte);
           __ sub(r0, r9, Operand(r0, LSL, kPointerSizeLog2));
           // r0: offset of first field after pre-allocated fields
           if (FLAG_debug_code) {
             __ cmp(r5, r0);
@@ skipping 1497 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM