[runtime] Add PropertyConstness bit to PropertyDetails.

src/map-updater.cc

 // Copyright 2017 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.
 
 #include "src/map-updater.h"
 
 #include "src/field-type.h"
 #include "src/handles.h"
 #include "src/isolate.h"
 #include "src/objects-inl.h"
 #include "src/objects.h"
 #include "src/transitions.h"
 
 namespace v8 {
 namespace internal {
 
 namespace {
 
 inline bool EqualImmutableValues(Object* obj1, Object* obj2) {
   if (obj1 == obj2) return true;  // Valid for both kData and kAccessor kinds.
   // TODO(ishell): compare AccessorPairs.
   return false;
 }
 
-inline bool LocationFitsInto(PropertyLocation what, PropertyLocation where) {
-  return where == kField || what == kDescriptor;
-}
-
 }  // namespace
 
 Name* MapUpdater::GetKey(int descriptor) const {
   return old_descriptors_->GetKey(descriptor);
 }
 
 PropertyDetails MapUpdater::GetDetails(int descriptor) const {
   DCHECK_LE(0, descriptor);
   if (descriptor == modified_descriptor_) {
     return PropertyDetails(new_kind_, new_attributes_, new_location_,
-                           new_representation_);
+                           new_constness_, new_representation_);
   }
   return old_descriptors_->GetDetails(descriptor);
 }
 
 Object* MapUpdater::GetValue(int descriptor) const {
   DCHECK_LE(0, descriptor);
   if (descriptor == modified_descriptor_) {
     DCHECK_EQ(kDescriptor, new_location_);
     return *new_value_;
   }
@@ skipping 41 matching lines @@
                                                PropertyAttributes attributes,
                                                Representation representation,
                                                Handle<FieldType> field_type) {
   DCHECK_EQ(kInitialized, state_);
   DCHECK_LE(0, descriptor);
   DCHECK(!old_map_->is_dictionary_map());
   modified_descriptor_ = descriptor;
   new_kind_ = kData;
   new_attributes_ = attributes;
   new_location_ = kField;
-  new_representation_ = representation;
-  new_field_type_ = field_type;
 
   PropertyDetails old_details =
       old_descriptors_->GetDetails(modified_descriptor_);
 
   // If property kind is not reconfigured merge the result with
   // representation/field type from the old descriptor.
   if (old_details.kind() == new_kind_) {
+    new_constness_ = old_details.constness();
+
     Representation old_representation = old_details.representation();
-    new_representation_ = new_representation_.generalize(old_representation);
+    new_representation_ = representation.generalize(old_representation);
 
     Handle<FieldType> old_field_type =
         GetOrComputeFieldType(old_descriptors_, modified_descriptor_,
                               old_details.location(), new_representation_);
 
-    new_field_type_ = Map::GeneralizeFieldType(
-        old_representation, old_field_type, new_representation_,
-        new_field_type_, isolate_);
+    new_field_type_ =
+        Map::GeneralizeFieldType(old_representation, old_field_type,
+                                 new_representation_, field_type, isolate_);
+  } else {
+    // We don't know if this is a first property kind reconfiguration
+    // and we don't know which value was in this property previously
+    // therefore we can't treat such a property as constant.
+    new_constness_ = kMutable;
+    new_representation_ = representation;
+    new_field_type_ = field_type;
   }
 
   if (TryRecofigureToDataFieldInplace() == kEnd) return result_map_;
   if (FindRootMap() == kEnd) return result_map_;
   if (FindTargetMap() == kEnd) return result_map_;
   ConstructNewMap();
   DCHECK_EQ(kEnd, state_);
   return result_map_;
 }
 
@@ skipping 91 matching lines @@
     return CopyGeneralizeAllFields("GenAll_InvalidElementsTransition");
   }
 
   if (modified_descriptor_ >= 0 && modified_descriptor_ < root_nof) {
     PropertyDetails old_details =
         old_descriptors_->GetDetails(modified_descriptor_);
     if (old_details.kind() != new_kind_ ||
         old_details.attributes() != new_attributes_) {
       return CopyGeneralizeAllFields("GenAll_RootModification1");
     }
-    if (!new_representation_.fits_into(old_details.representation())) {
+    if (old_details.location() != kField) {
       return CopyGeneralizeAllFields("GenAll_RootModification2");
     }
-    if (old_details.location() != kField) {
+    DCHECK_EQ(kMutable, old_details.constness());
+    if (!new_representation_.fits_into(old_details.representation())) {
       return CopyGeneralizeAllFields("GenAll_RootModification3");
     }
     DCHECK_EQ(kData, old_details.kind());
     DCHECK_EQ(kData, new_kind_);
     DCHECK_EQ(kField, new_location_);
     FieldType* old_field_type =
         old_descriptors_->GetFieldType(modified_descriptor_);
     if (!new_field_type_->NowIs(old_field_type)) {
       return CopyGeneralizeAllFields("GenAll_RootModification4");
     }
@@ skipping 24 matching lines @@
 
     // Check if target map is incompatible.
     PropertyDetails tmp_details = tmp_descriptors->GetDetails(i);
     DCHECK_EQ(old_details.kind(), tmp_details.kind());
     DCHECK_EQ(old_details.attributes(), tmp_details.attributes());
     if (old_details.kind() == kAccessor &&
         !EqualImmutableValues(GetValue(i), tmp_descriptors->GetValue(i))) {
       // TODO(ishell): mutable accessors are not implemented yet.
       return CopyGeneralizeAllFields("GenAll_Incompatible");
     }
+    // Check if old constness fits into tmp constness.
+    if (!IsGeneralizableTo(old_details.constness(), tmp_details.constness())) {
+      break;
+    }
     // Check if old location fits into tmp location.
-    if (!LocationFitsInto(old_details.location(), tmp_details.location())) {
+    if (!IsGeneralizableTo(old_details.location(), tmp_details.location())) {
       break;
     }
 
     // Check if old representation fits into tmp representation.
     Representation tmp_representation = tmp_details.representation();
     if (!old_details.representation().fits_into(tmp_representation)) {
       break;
     }
 
     if (tmp_details.location() == kField) {
@@ skipping 43 matching lines @@
 
   // Find the last compatible target map in the transition tree.
   for (int i = target_nof; i < old_nof_; ++i) {
     PropertyDetails old_details = GetDetails(i);
     Map* transition = TransitionArray::SearchTransition(
         *target_map_, old_details.kind(), GetKey(i), old_details.attributes());
     if (transition == NULL) break;
     Handle<Map> tmp_map(transition, isolate_);
     Handle<DescriptorArray> tmp_descriptors(tmp_map->instance_descriptors(),
                                             isolate_);
-
 #ifdef DEBUG
     // Check that target map is compatible.
     PropertyDetails tmp_details = tmp_descriptors->GetDetails(i);
     DCHECK_EQ(old_details.kind(), tmp_details.kind());
     DCHECK_EQ(old_details.attributes(), tmp_details.attributes());
 #endif
     if (old_details.kind() == kAccessor &&
         !EqualImmutableValues(GetValue(i), tmp_descriptors->GetValue(i))) {
       return CopyGeneralizeAllFields("GenAll_Incompatible");
     }
@@ skipping 42 matching lines @@
 
   // Merge "updated" old_descriptor entries with target_descriptor entries.
   // |root_nof| -> |target_nof|
   for (int i = root_nof; i < target_nof; ++i) {
     Handle<Name> key(GetKey(i), isolate_);
     PropertyDetails old_details = GetDetails(i);
     PropertyDetails target_details = target_descriptors->GetDetails(i);
 
     PropertyKind next_kind = old_details.kind();
     PropertyAttributes next_attributes = old_details.attributes();
+    DCHECK_EQ(next_kind, target_details.kind());
+    DCHECK_EQ(next_attributes, target_details.attributes());
+
+    PropertyConstness next_constness = GeneralizeConstness(
+        old_details.constness(), target_details.constness());
+
+    // Note: failed values equality check does not invalidate per-object
+    // property constness.
     PropertyLocation next_location =
         old_details.location() == kField ||
                 target_details.location() == kField ||
                 !EqualImmutableValues(target_descriptors->GetValue(i),
                                       GetValue(i))
             ? kField
             : kDescriptor;
 
+    // TODO(ishell): remove once constant field tracking is done.
+    if (next_location == kField) next_constness = kMutable;
+    // Ensure that mutable values are stored in fields.
+    DCHECK_IMPLIES(next_constness == kMutable, next_location == kField);
+
     Representation next_representation =
         old_details.representation().generalize(
             target_details.representation());
 
-    DCHECK_EQ(next_kind, target_details.kind());
-    DCHECK_EQ(next_attributes, target_details.attributes());
-
     if (next_location == kField) {
       Handle<FieldType> old_field_type =
           GetOrComputeFieldType(i, old_details.location(), next_representation);
 
       Handle<FieldType> target_field_type =
           GetOrComputeFieldType(target_descriptors, i,
                                 target_details.location(), next_representation);
 
       Handle<FieldType> next_field_type = Map::GeneralizeFieldType(
           old_details.representation(), old_field_type, next_representation,
           target_field_type, isolate_);
 
       Handle<Object> wrapped_type(Map::WrapFieldType(next_field_type));
       Descriptor d;
       if (next_kind == kData) {
-        d = Descriptor::DataField(key, current_offset, wrapped_type,
-                                  next_attributes, next_representation);
+        d = Descriptor::DataField(key, current_offset, next_attributes,
+                                  next_constness, next_representation,
+                                  wrapped_type);
       } else {
         // TODO(ishell): mutable accessors are not implemented yet.
         UNIMPLEMENTED();
       }
       current_offset += d.GetDetails().field_width_in_words();
       new_descriptors->Set(i, &d);
     } else {
       DCHECK_EQ(kDescriptor, next_location);
+      DCHECK_EQ(kConst, next_constness);
 
       Handle<Object> value(GetValue(i), isolate_);
       Descriptor d;
       if (next_kind == kData) {
         d = Descriptor::DataConstant(key, value, next_attributes);
       } else {
         DCHECK_EQ(kAccessor, next_kind);
         d = Descriptor::AccessorConstant(key, value, next_attributes);
       }
       new_descriptors->Set(i, &d);
     }
   }
 
   // Take "updated" old_descriptor entries.
   // |target_nof| -> |old_nof|
   for (int i = target_nof; i < old_nof_; ++i) {
     PropertyDetails old_details = GetDetails(i);
     Handle<Name> key(GetKey(i), isolate_);
 
     PropertyKind next_kind = old_details.kind();
     PropertyAttributes next_attributes = old_details.attributes();
+    PropertyConstness next_constness = old_details.constness();
     PropertyLocation next_location = old_details.location();
     Representation next_representation = old_details.representation();
 
     Descriptor d;
     if (next_location == kField) {
+      DCHECK_EQ(kMutable, next_constness);
       Handle<FieldType> old_field_type =
           GetOrComputeFieldType(i, old_details.location(), next_representation);
 
       Handle<Object> wrapped_type(Map::WrapFieldType(old_field_type));
       Descriptor d;
       if (next_kind == kData) {
-        d = Descriptor::DataField(key, current_offset, wrapped_type,
-                                  next_attributes, next_representation);
+        d = Descriptor::DataField(key, current_offset, next_attributes,
+                                  next_constness, next_representation,
+                                  wrapped_type);
       } else {
         // TODO(ishell): mutable accessors are not implemented yet.
         UNIMPLEMENTED();
       }
       current_offset += d.GetDetails().field_width_in_words();
       new_descriptors->Set(i, &d);
     } else {
       DCHECK_EQ(kDescriptor, next_location);
+      DCHECK_EQ(kConst, next_constness);
 
       Handle<Object> value(GetValue(i), isolate_);
       if (next_kind == kData) {
         d = Descriptor::DataConstant(key, value, next_attributes);
       } else {
         DCHECK_EQ(kAccessor, next_kind);
         d = Descriptor::AccessorConstant(key, value, next_attributes);
       }
       new_descriptors->Set(i, &d);
     }
@@ skipping 12 matching lines @@
     Name* name = descriptors->GetKey(i);
     PropertyDetails details = descriptors->GetDetails(i);
     Map* next = TransitionArray::SearchTransition(current, details.kind(), name,
                                                   details.attributes());
     if (next == NULL) break;
     DescriptorArray* next_descriptors = next->instance_descriptors();
 
     PropertyDetails next_details = next_descriptors->GetDetails(i);
     DCHECK_EQ(details.kind(), next_details.kind());
     DCHECK_EQ(details.attributes(), next_details.attributes());
+    if (details.constness() != next_details.constness()) break;
     if (details.location() != next_details.location()) break;
     if (!details.representation().Equals(next_details.representation())) break;
 
     if (next_details.location() == kField) {
       FieldType* next_field_type = next_descriptors->GetFieldType(i);
       if (!descriptors->GetFieldType(i)->NowIs(next_field_type)) {
         break;
       }
     } else {
       if (!EqualImmutableValues(descriptors->GetValue(i),
@@ skipping 75 matching lines @@
   // the new descriptors to maintain descriptors sharing invariant.
   split_map->ReplaceDescriptors(*new_descriptors, *new_layout_descriptor);
 
   result_map_ = new_map;
   state_ = kEnd;
   return state_;  // Done.
 }
 
 }  // namespace internal
 }  // namespace v8