Reland "In-object double fields unboxing (for 64-bit only)."

src/objects-printer.cc

Index: src/objects-printer.cc
diff --git a/src/objects-printer.cc b/src/objects-printer.cc
index 2fb924cfc99a19b94d964ddd364c7545d16f3d81..bc5ffca78eed6c6d572ef183bd7f1d998c7cc9a7 100644
--- a/src/objects-printer.cc
+++ b/src/objects-printer.cc
@@ -233,8 +233,12 @@ void JSObject::PrintProperties(std::ostream& os) {  // NOLINT
       switch (descs->GetType(i)) {
         case FIELD: {
           FieldIndex index = FieldIndex::ForDescriptor(map(), i);
-          os << Brief(RawFastPropertyAt(index)) << " (field at offset "
-             << index.property_index() << ")\n";
+          if (IsUnboxedDoubleField(index)) {
+            os << "<unboxed double> " << RawFastDoublePropertyAt(index);
+          } else {
+            os << Brief(RawFastPropertyAt(index));
+          }
+          os << " (field at offset " << index.property_index() << ")\n";
           break;
         }
         case CONSTANT:
@@ -430,6 +434,9 @@ void Map::MapPrint(std::ostream& os) {  // NOLINT
   os << "\n - instance descriptors " << (owns_descriptors() ? "(own) " : "")
      << "#" << NumberOfOwnDescriptors() << ": "
      << Brief(instance_descriptors());
+  if (FLAG_unbox_double_fields) {
+    os << "\n - layout descriptor: " << Brief(layout_descriptor());
+  }
   if (HasTransitionArray()) {
     os << "\n - transitions: " << Brief(transitions());
   }
@@ -1076,6 +1083,43 @@ void DescriptorArray::PrintDescriptors(std::ostream& os) {  // NOLINT
 }
 
 
+static void PrintBitMask(std::ostream& os, uint32_t value) {  // NOLINT
+  for (int i = 0; i < 32; i++) {
+    if ((i & 7) == 0) os << " ";
+    os << (((value & 1) == 0) ? "_" : "x");
+    value >>= 1;
+  }
+}
+
+
+void LayoutDescriptor::Print() {
+  OFStream os(stdout);
+  this->Print(os);
+  os << std::flush;
+}
+
+
+void LayoutDescriptor::Print(std::ostream& os) {  // NOLINT
+  os << "Layout descriptor: ";
+  if (IsUninitialized()) {
+    os << "<uninitialized>";
+  } else if (IsFastPointerLayout()) {
+    os << "<all tagged>";
+  } else if (IsSmi()) {
+    os << "fast";
+    PrintBitMask(os, static_cast<uint32_t>(Smi::cast(this)->value()));
+  } else {
+    os << "slow";
+    int len = length();
+    for (int i = 0; i < len; i++) {
+      if (i > 0) os << " |";
+      PrintBitMask(os, get_scalar(i));
+    }
+  }
+  os << "\n";
+}
+
+
 void TransitionArray::Print() {
   OFStream os(stdout);
   this->PrintTransitions(os);