Fix object initialization when slack tracking for it's map is still enabled.

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 408 matching lines @@
 
           __ bind(&allocate);
         }
 
         // Now allocate the JSObject on the heap.
         // r1: constructor function
         // r2: initial map
         Label rt_call_reload_new_target;
         __ ldrb(r3, FieldMemOperand(r2, Map::kInstanceSizeOffset));
 
-        __ Allocate(r3, r4, r5, r6, &rt_call_reload_new_target, SIZE_IN_WORDS);
+        __ Allocate(r3, r4, r7, r6, &rt_call_reload_new_target, 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.
         // r1: constructor function
         // r2: initial map
         // r3: object size
         // r4: JSObject (not tagged)
+        // r7: start of next object
         __ LoadRoot(r6, Heap::kEmptyFixedArrayRootIndex);
         __ mov(r5, r4);
-        DCHECK_EQ(0 * kPointerSize, JSObject::kMapOffset);
+        STATIC_ASSERT(0 * kPointerSize == JSObject::kMapOffset);
         __ str(r2, MemOperand(r5, kPointerSize, PostIndex));
-        DCHECK_EQ(1 * kPointerSize, JSObject::kPropertiesOffset);
+        STATIC_ASSERT(1 * kPointerSize == JSObject::kPropertiesOffset);
         __ str(r6, MemOperand(r5, kPointerSize, PostIndex));
-        DCHECK_EQ(2 * kPointerSize, JSObject::kElementsOffset);
+        STATIC_ASSERT(2 * kPointerSize == JSObject::kElementsOffset);
         __ str(r6, MemOperand(r5, kPointerSize, PostIndex));
 
         // Fill all the in-object properties with the appropriate filler.
         // r1: constructor function
         // r2: initial map
         // r3: object size
         // r4: JSObject (not tagged)
         // r5: First in-object property of JSObject (not tagged)
         DCHECK_EQ(3 * kPointerSize, JSObject::kHeaderSize);
         __ LoadRoot(r6, Heap::kUndefinedValueRootIndex);
 
         if (!is_api_function) {
           Label no_inobject_slack_tracking;
 
           // Check if slack tracking is enabled.
           __ ldr(ip, FieldMemOperand(r2, Map::kBitField3Offset));
           __ DecodeField<Map::Counter>(ip);
           __ cmp(ip, Operand(Map::kSlackTrackingCounterEnd));
           __ b(lt, &no_inobject_slack_tracking);
 
           // Allocate object with a slack.
-          __ ldr(r0, FieldMemOperand(r2, Map::kInstanceSizesOffset));
-          __ Ubfx(r0, r0,
-                  Map::kInObjectPropertiesOrConstructorFunctionIndexByte *
-                      kBitsPerByte,
-                  kBitsPerByte);
+          // See comment on JSObject::InitializeBody() for details.
           __ ldr(r2, FieldMemOperand(r2, Map::kInstanceAttributesOffset));
           __ Ubfx(r2, r2, Map::kUnusedPropertyFieldsByte * kBitsPerByte,
                   kBitsPerByte);
-          __ sub(r0, r0, Operand(r2));
-          __ add(r0, r5, Operand(r0, LSL, kPointerSizeLog2));
+          __ sub(r0, r7, Operand(r2, LSL, kPointerSizeLog2));
           // r0: offset of first field after pre-allocated fields
           if (FLAG_debug_code) {
-            __ add(ip, r4,
-                   Operand(r3, LSL, kPointerSizeLog2));  // End of object.
-            __ cmp(r0, ip);
+            __ cmp(r5, r0);
             __ Assert(le, kUnexpectedNumberOfPreAllocatedPropertyFields);
           }
           __ InitializeFieldsWithFiller(r5, r0, r6);
           // To allow for truncation.
           __ LoadRoot(r6, Heap::kOnePointerFillerMapRootIndex);
           // Fill the remaining fields with one pointer filler map.
 
           __ bind(&no_inobject_slack_tracking);
         }
 
-        __ add(r0, r4, Operand(r3, LSL, kPointerSizeLog2));  // End of object.
-        __ InitializeFieldsWithFiller(r5, r0, r6);
+        __ InitializeFieldsWithFiller(r5, r7, r6);
 
         // 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(r4, r4, Operand(kHeapObjectTag));
 
         // Continue with JSObject being successfully allocated
         // r4: JSObject
         __ jmp(&allocated);
 
         // Reload the new target and fall-through.
@@ skipping 1341 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM