VM: Reland Inline instance object hash code into object header on 64bit.

runtime/vm/assembler_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // NOLINT
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
@@ skipping 3415 matching lines @@
     addq(instance_reg, Immediate(instance_size));
     // instance_reg: potential next object start.
     cmpq(instance_reg, Address(temp, Heap::EndOffset(space)));
     j(ABOVE_EQUAL, failure, near_jump);
     // Successfully allocated the object, now update top to point to
     // next object start and store the class in the class field of object.
     movq(Address(temp, Heap::TopOffset(space)), instance_reg);
     NOT_IN_PRODUCT(UpdateAllocationStats(cls.id(), space));
     ASSERT(instance_size >= kHeapObjectTag);
     AddImmediate(instance_reg, Immediate(kHeapObjectTag - instance_size));
-    uword tags = 0;
+    uint32_t tags = 0;
     tags = RawObject::SizeTag::update(instance_size, tags);
     ASSERT(cls.id() != kIllegalCid);
     tags = RawObject::ClassIdTag::update(cls.id(), tags);
+    // Extends the 32 bit tags with zeros, which is the uninitialized
+    // hash code.
     MoveImmediate(FieldAddress(instance_reg, Object::tags_offset()),
                   Immediate(tags));
   } else {
     jmp(failure);
   }
 }
 
 
 void Assembler::TryAllocateArray(intptr_t cid,
                                  intptr_t instance_size,
@@ skipping 23 matching lines @@
     j(ABOVE_EQUAL, failure);
 
     // Successfully allocated the object(s), now update top to point to
     // next object start and initialize the object.
     movq(Address(temp, Heap::TopOffset(space)), end_address);
     addq(instance, Immediate(kHeapObjectTag));
     NOT_IN_PRODUCT(UpdateAllocationStatsWithSize(cid, instance_size, space));
 
     // Initialize the tags.
     // instance: new object start as a tagged pointer.
-    uword tags = 0;
+    uint32_t tags = 0;
     tags = RawObject::ClassIdTag::update(cid, tags);
     tags = RawObject::SizeTag::update(instance_size, tags);
+    // Extends the 32 bit tags with zeros, which is the uninitialized
+    // hash code.
     movq(FieldAddress(instance, Array::tags_offset()), Immediate(tags));
   } else {
     jmp(failure);
   }
 }
 
 void Assembler::Align(int alignment, intptr_t offset) {
   ASSERT(Utils::IsPowerOfTwo(alignment));
   intptr_t pos = offset + buffer_.GetPosition();
   int mod = pos & (alignment - 1);
@@ skipping 305 matching lines @@
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64