Reapply descriptor array sharing.

src/ia32/macro-assembler-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2558 matching lines @@
   // will not return here
   int3();
 }
 
 
 void MacroAssembler::LoadInstanceDescriptors(Register map,
                                              Register descriptors) {
   Register temp = descriptors;
   mov(temp, FieldOperand(map, Map::kTransitionsOrBackPointerOffset));
 
-  Label ok, fail;
+  Label ok, fail, load_from_back_pointer;
   CheckMap(temp,
            isolate()->factory()->fixed_array_map(),
            &fail,
            DONT_DO_SMI_CHECK);
-  mov(descriptors, FieldOperand(temp, TransitionArray::kDescriptorsOffset));
+  mov(temp, FieldOperand(temp, TransitionArray::kDescriptorsPointerOffset));
+  mov(descriptors, FieldOperand(temp, JSGlobalPropertyCell::kValueOffset));
   jmp(&ok);
+
   bind(&fail);
+  cmp(temp, isolate()->factory()->undefined_value());
+  j(not_equal, &load_from_back_pointer, Label::kNear);
   mov(descriptors, isolate()->factory()->empty_descriptor_array());
+  jmp(&ok);
+
+  bind(&load_from_back_pointer);
+  mov(temp, FieldOperand(temp, Map::kTransitionsOrBackPointerOffset));
+  mov(temp, FieldOperand(temp, TransitionArray::kDescriptorsPointerOffset));
+  mov(descriptors, FieldOperand(temp, JSGlobalPropertyCell::kValueOffset));
+
   bind(&ok);
 }
 
 
+void MacroAssembler::NumberOfOwnDescriptors(Register dst, Register map) {
+  mov(dst, FieldOperand(map, Map::kBitField3Offset));
+  DecodeField<Map::NumberOfOwnDescriptorsBits>(dst);
+}
+
+
 void MacroAssembler::LoadPowerOf2(XMMRegister dst,
                                   Register scratch,
                                   int power) {
   ASSERT(is_uintn(power + HeapNumber::kExponentBias,
                   HeapNumber::kExponentBits));
   mov(scratch, Immediate(power + HeapNumber::kExponentBias));
   movd(dst, scratch);
   psllq(dst, HeapNumber::kMantissaBits);
 }
 
@@ skipping 369 matching lines @@
   j(not_equal, call_runtime);
 
   mov(ecx, FieldOperand(ebx, Map::kPrototypeOffset));
   cmp(ecx, isolate()->factory()->null_value());
   j(not_equal, &next);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32