Fix inobject slack tracking for both subclassing and non-subclassing cases.

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 376 matching lines @@
         __ Cmp(constructor, x10);
         __ B(ne, &rt_call);
 
         // Check that the constructor is not constructing a JSFunction (see
         // comments in Runtime_NewObject in runtime.cc). In which case the
         // initial
         // map's instance type would be JS_FUNCTION_TYPE.
         __ CompareInstanceType(init_map, x10, JS_FUNCTION_TYPE);
         __ B(eq, &rt_call);
 
-        Register constructon_count = x14;
-        if (!is_api_function) {
-          Label allocate;
-          MemOperand bit_field3 =
-              FieldMemOperand(init_map, Map::kBitField3Offset);
-          // Check if slack tracking is enabled.
-          __ Ldr(x4, bit_field3);
-          __ DecodeField<Map::Counter>(constructon_count, x4);
-          __ Cmp(constructon_count, Operand(Map::kSlackTrackingCounterEnd));
-          __ B(lt, &allocate);
-          // Decrease generous allocation count.
-          __ Subs(x4, x4, Operand(1 << Map::Counter::kShift));
-          __ Str(x4, bit_field3);
-          __ Cmp(constructon_count, Operand(Map::kSlackTrackingCounterEnd));
-          __ B(ne, &allocate);
-
-          // Push the constructor, new_target and map to the stack, and
-          // the map again as an argument to the runtime call.
-          __ Push(constructor, new_target, init_map, init_map);
-          __ CallRuntime(Runtime::kFinalizeInstanceSize, 1);
-          __ Pop(init_map, new_target, constructor);
-          __ Mov(constructon_count, Operand(Map::kSlackTrackingCounterEnd - 1));
-          __ Bind(&allocate);
-        }
-
         // Now allocate the JSObject on the heap.
         Register obj_size = x10;
         Register new_obj = x4;
         Register next_obj = obj_size;  // May overlap.
         __ Ldrb(obj_size, FieldMemOperand(init_map, Map::kInstanceSizeOffset));
         __ Allocate(obj_size, new_obj, next_obj, x11, &rt_call, SIZE_IN_WORDS);
 
         // Allocated the JSObject, now initialize the fields. Map is set to
         // initial map and properties and elements are set to empty fixed array.
         // NB. the object pointer is not tagged, so MemOperand is used.
         Register write_address = x5;
         Register empty = x7;
         __ Mov(write_address, new_obj);
         __ LoadRoot(empty, Heap::kEmptyFixedArrayRootIndex);
         STATIC_ASSERT(0 * kPointerSize == JSObject::kMapOffset);
         __ Str(init_map, MemOperand(write_address, kPointerSize, PostIndex));
         STATIC_ASSERT(1 * kPointerSize == JSObject::kPropertiesOffset);
         STATIC_ASSERT(2 * kPointerSize == JSObject::kElementsOffset);
         __ Stp(empty, empty,
                MemOperand(write_address, 2 * kPointerSize, PostIndex));
         STATIC_ASSERT(3 * kPointerSize == JSObject::kHeaderSize);
 
+        // Add the object tag to make the JSObject real, so that we can continue
+        // and jump into the continuation code at any time from now on.
+        __ Add(new_obj, new_obj, kHeapObjectTag);
+
         // Fill all of the in-object properties with the appropriate filler.
         Register filler = x7;
         __ 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);
           __ Cmp(constructon_count, Operand(Map::kSlackTrackingCounterEnd));
           __ B(lt, &no_inobject_slack_tracking);
-          constructon_count = NoReg;
+          // Decrease generous allocation count.
+          __ Subs(x11, x11, Operand(1 << Map::Counter::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;
           __ Sub(end_of_pre_allocated, next_obj,
                  Operand(unused_props, LSL, kPointerSizeLog2));
           unused_props = NoReg;
 
           if (FLAG_debug_code) {
             __ Cmp(write_address, end_of_pre_allocated);
             __ Assert(le, kUnexpectedNumberOfPreAllocatedPropertyFields);
           }
 
           // Fill the pre-allocated fields with undef.
           __ InitializeFieldsWithFiller(write_address, end_of_pre_allocated,
                                         filler);
 
           // Fill the remaining fields with one pointer filler map.
           __ LoadRoot(filler, Heap::kOnePointerFillerMapRootIndex);
+          __ InitializeFieldsWithFiller(write_address, next_obj, filler);
+
+          __ Cmp(constructon_count, Operand(Map::kSlackTrackingCounterEnd));
+          __ B(ne, &allocated);
+
+          // Push the constructor, new_target and the object to the stack,
+          // and then the initial map as an argument to the runtime call.
+          __ Push(constructor, new_target, new_obj, init_map);
+          __ CallRuntime(Runtime::kFinalizeInstanceSize, 1);
+          __ Pop(new_obj, new_target, constructor);
+
+          // Continue with JSObject being successfully allocated.
+          __ B(&allocated);
 
           __ bind(&no_inobject_slack_tracking);
         }
 
-        // Fill all of the property fields with undef.
         __ InitializeFieldsWithFiller(write_address, next_obj, filler);
 
-        // Add the object tag to make the JSObject real, so that we can continue
-        // and jump into the continuation code at any time from now on.
-        __ Add(new_obj, new_obj, kHeapObjectTag);
-
         // Continue with JSObject being successfully allocated.
         __ B(&allocated);
       }
 
       // Allocate the new receiver object using the runtime call.
       // x1: constructor function
       // x3: new target
       __ Bind(&rt_call);
 
       // Push the constructor and new_target twice, second pair as arguments
@@ skipping 1543 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM