[FragmentItem] Merge items_ and offsets_ vector in NGFragmentItemsBuilder

To improve the performance of |NGFragmentItemsBuilder|:

1. This patch merges two vectors (items and offsets) to one.
   This is the same as r664158 <crrev.com/c/1633019> did to
   |NGContainerFragmentBuilder|.
2. This patch gives an inline size to the vector to reduce
   memory allocations.

The allocations of these two vectors is hot in text-heavy
benchmarks. This patch improves:
* chapter-reflow by ~5%.
* line-layout-repeat-append by ~15%.
These tests are currently slower when FragmentItem is enabled.

https://pinpoint-dot-chromeperf.appspot.com/job/11669b69e20000

Bug: 982194
Change-Id: I2c787438abc4c2484fe9ae432447ecd30ee4a0fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2142668
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758469}

third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items.cc

@@ -21,14 +21,14 @@ NGFragmentItems::NGFragmentItems(NGFragmentItemsBuilder* builder)
     : text_content_(std::move(builder->text_content_)),
       first_line_text_content_(std::move(builder->first_line_text_content_)),
       size_(builder->items_.size()) {
-  Vector<scoped_refptr<const NGFragmentItem>>& source_items = builder->items_;
+  NGFragmentItemsBuilder::ItemWithOffsetList& source_items = builder->items_;
   for (unsigned i = 0; i < size_; ++i) {
     // Call the move constructor to move without |AddRef|. Items in
     // |NGFragmentItemsBuilder| are not used after |this| was constructed.
-    DCHECK(source_items[i]);
+    DCHECK(source_items[i].item);
     new (&items_[i])
-        scoped_refptr<const NGFragmentItem>(std::move(source_items[i]));
-    DCHECK(!source_items[i]);  // Ensure the source was moved.
+        scoped_refptr<const NGFragmentItem>(std::move(source_items[i].item));
+    DCHECK(!source_items[i].item);  // Ensure the source was moved.
   }
 }
 

third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.cc

@@ -30,7 +30,6 @@ void NGFragmentItemsBuilder::SetCurrentLine(
 
 void NGFragmentItemsBuilder::AddLine(const NGPhysicalLineBoxFragment& line,
                                      const LogicalOffset& offset) {
-  DCHECK_EQ(items_.size(), offsets_.size());
   DCHECK(!is_converted_to_physical_);
 #if DCHECK_IS_ON()
   DCHECK_EQ(current_line_fragment_, &line);
@@ -40,18 +39,17 @@ void NGFragmentItemsBuilder::AddLine(const NGPhysicalLineBoxFragment& line,
   const wtf_size_t size_before = items_.size();
   const wtf_size_t capacity = size_before + current_line_.size() + 1;
   items_.ReserveCapacity(capacity);
-  offsets_.ReserveCapacity(capacity);
 
   // Add an empty item so that the start of the line can be set later.
   const wtf_size_t line_start_index = items_.size();
-  items_.Grow(line_start_index + 1);
-  offsets_.push_back(offset);
+  items_.emplace_back(offset);
 
   AddItems(current_line_.begin(), current_line_.end());
 
   // All children are added. Create an item for the start of the line.
   const wtf_size_t item_count = items_.size() - line_start_index;
-  items_[line_start_index] =
+  DCHECK(!items_[line_start_index].item);
+  items_[line_start_index].item =
       base::MakeRefCounted<NGFragmentItem>(line, item_count);
 
   // Keep children's offsets relative to |line|. They will be adjusted later in
@@ -62,19 +60,17 @@ void NGFragmentItemsBuilder::AddLine(const NGPhysicalLineBoxFragment& line,
   current_line_fragment_ = nullptr;
 #endif
 
-  DCHECK_EQ(items_.size(), offsets_.size());
   DCHECK_LE(items_.size(), capacity);
 }
 
 void NGFragmentItemsBuilder::AddItems(Child* child_begin, Child* child_end) {
-  DCHECK_EQ(items_.size(), offsets_.size());
   DCHECK(!is_converted_to_physical_);
 
   for (Child* child_iter = child_begin; child_iter != child_end;) {
     Child& child = *child_iter;
     if (const NGPhysicalTextFragment* text = child.fragment.get()) {
-      items_.push_back(base::MakeRefCounted<NGFragmentItem>(*text));
-      offsets_.push_back(child.rect.offset);
+      items_.emplace_back(base::MakeRefCounted<NGFragmentItem>(*text),
+                          child.rect.offset);
       ++child_iter;
       continue;
     }
@@ -97,8 +93,7 @@ void NGFragmentItemsBuilder::AddItems(Child* child_begin, Child* child_end) {
 
       // Take the fast path when we know |child| does not have child items.
       if (child.children_count <= 1) {
-        items_.push_back(std::move(item));
-        offsets_.push_back(child.rect.offset);
+        items_.emplace_back(std::move(item), child.rect.offset);
         ++child_iter;
         continue;
       }
@@ -109,8 +104,7 @@ void NGFragmentItemsBuilder::AddItems(Child* child_begin, Child* child_end) {
       //
       // Add an empty item so that the start of the box can be set later.
       wtf_size_t box_start_index = items_.size();
-      items_.Grow(box_start_index + 1);
-      offsets_.push_back(child.rect.offset);
+      items_.emplace_back(child.rect.offset);
 
       // Add all children, including their desendants, skipping this item.
       CHECK_GE(child.children_count, 1u);  // 0 will loop infinitely.
@@ -125,7 +119,8 @@ void NGFragmentItemsBuilder::AddItems(Child* child_begin, Child* child_end) {
 
       // Create an item for the start of the box.
       item->SetDescendantsCount(item_count);
-      items_[box_start_index] = std::move(item);
+      DCHECK(!items_[box_start_index].item);
+      items_[box_start_index].item = std::move(item);
       continue;
     }
 
@@ -144,9 +139,9 @@ void NGFragmentItemsBuilder::AddListMarker(
   // Resolved direction matters only for inline items, and outside list markers
   // are not inline.
   const TextDirection resolved_direction = TextDirection::kLtr;
-  items_.push_back(base::MakeRefCounted<NGFragmentItem>(marker_fragment,
-                                                        resolved_direction));
-  offsets_.push_back(offset);
+  items_.emplace_back(
+      base::MakeRefCounted<NGFragmentItem>(marker_fragment, resolved_direction),
+      offset);
 }
 
 void NGFragmentItemsBuilder::AddItems(const NGFragmentItems& items,
@@ -154,27 +149,29 @@ void NGFragmentItemsBuilder::AddItems(const NGFragmentItems& items,
                                       TextDirection direction,
                                       const PhysicalSize& container_size) {
   DCHECK(items_.IsEmpty());
-  items_.Append(items.Items().data(), items.Size());
+  const NGFragmentItems::Span source_items = items.Items();
+  const wtf_size_t estimated_size = source_items.size();
+  items_.ReserveCapacity(estimated_size);
 
   // Convert offsets to logical. The logic is opposite to |ConvertToPhysical|.
   // This is needed because the container size may be different, in that case,
   // the physical offsets are different when `writing-mode: vertial-rl`.
   DCHECK(!is_converted_to_physical_);
-  DCHECK(offsets_.IsEmpty());
-  offsets_.ReserveCapacity(items.Items().size());
   const WritingMode line_writing_mode = ToLineWritingMode(writing_mode);
   for (NGInlineCursor cursor(items); cursor;) {
     DCHECK(cursor.Current().Item());
     const NGFragmentItem& item = *cursor.Current().Item();
-    offsets_.push_back(item.OffsetInContainerBlock().ConvertToLogical(
-        writing_mode, direction, container_size, item.Size()));
+    items_.emplace_back(
+        &item, item.OffsetInContainerBlock().ConvertToLogical(
+                   writing_mode, direction, container_size, item.Size()));
 
     if (item.Type() == NGFragmentItem::kLine) {
       const PhysicalRect line_box_bounds = item.RectInContainerBlock();
       for (NGInlineCursor line_children = cursor.CursorForDescendants();
            line_children; line_children.MoveToNext()) {
         const NGFragmentItem& line_child = *line_children.Current().Item();
-        offsets_.push_back(
+        items_.emplace_back(
+            &line_child,
             (line_child.OffsetInContainerBlock() - line_box_bounds.offset)
                 .ConvertToLogical(line_writing_mode, TextDirection::kLtr,
                                   line_box_bounds.size, line_child.Size()));
@@ -185,16 +182,17 @@ void NGFragmentItemsBuilder::AddItems(const NGFragmentItems& items,
 
     cursor.MoveToNext();
   }
+  DCHECK_LE(items_.size(), estimated_size);
 
   DCHECK(!text_content_);
   text_content_ = items.Text(false);
   first_line_text_content_ = items.Text(true);
 }
 
-const Vector<scoped_refptr<const NGFragmentItem>>&
-NGFragmentItemsBuilder::Items(WritingMode writing_mode,
-                              TextDirection direction,
-                              const PhysicalSize& outer_size) {
+const NGFragmentItemsBuilder::ItemWithOffsetList& NGFragmentItemsBuilder::Items(
+    WritingMode writing_mode,
+    TextDirection direction,
+    const PhysicalSize& outer_size) {
   ConvertToPhysical(writing_mode, direction, outer_size);
   return items_;
 }
@@ -204,7 +202,6 @@ NGFragmentItemsBuilder::Items(WritingMode writing_mode,
 void NGFragmentItemsBuilder::ConvertToPhysical(WritingMode writing_mode,
                                                TextDirection direction,
                                                const PhysicalSize& outer_size) {
-  CHECK_EQ(items_.size(), offsets_.size());
   if (is_converted_to_physical_)
     return;
 
@@ -212,13 +209,10 @@ void NGFragmentItemsBuilder::ConvertToPhysical(WritingMode writing_mode,
   // convert their logical offsets.
   const WritingMode line_writing_mode = ToLineWritingMode(writing_mode);
 
-  scoped_refptr<const NGFragmentItem>* item_iter = items_.begin();
-  const LogicalOffset* offset = offsets_.begin();
-  for (; item_iter != items_.end(); ++item_iter, ++offset) {
-    DCHECK_NE(offset, offsets_.end());
-    const NGFragmentItem* item = item_iter->get();
-    const_cast<NGFragmentItem*>(item)->SetOffset(offset->ConvertToPhysical(
-        writing_mode, direction, outer_size, item->Size()));
+  for (ItemWithOffset* iter = items_.begin(); iter != items_.end(); ++iter) {
+    NGFragmentItem* item = const_cast<NGFragmentItem*>(iter->item.get());
+    item->SetOffset(iter->offset.ConvertToPhysical(writing_mode, direction,
+                                                   outer_size, item->Size()));
 
     // Transform children of lines separately from children of the block,
     // because they may have different directions from the block. To do
@@ -229,17 +223,15 @@ void NGFragmentItemsBuilder::ConvertToPhysical(WritingMode writing_mode,
       if (descendants_count) {
         const PhysicalRect line_box_bounds = item->RectInContainerBlock();
         while (--descendants_count) {
-          ++offset;
-          ++item_iter;
-          DCHECK_NE(offset, offsets_.end());
-          DCHECK_NE(item_iter, items_.end());
-          item = item_iter->get();
+          ++iter;
+          DCHECK_NE(iter, items_.end());
+          item = const_cast<NGFragmentItem*>(iter->item.get());
           // Use `kLtr` because inline items are after bidi-reoder, and that
           // their offset is visual, not logical.
-          const_cast<NGFragmentItem*>(item)->SetOffset(
-              offset->ConvertToPhysical(line_writing_mode, TextDirection::kLtr,
-                                        line_box_bounds.size, item->Size()) +
-              line_box_bounds.offset);
+          item->SetOffset(iter->offset.ConvertToPhysical(
+                              line_writing_mode, TextDirection::kLtr,
+                              line_box_bounds.size, item->Size()) +
+                          line_box_bounds.offset);
         }
       }
     }
@@ -250,10 +242,9 @@ void NGFragmentItemsBuilder::ConvertToPhysical(WritingMode writing_mode,
 
 base::Optional<LogicalOffset> NGFragmentItemsBuilder::LogicalOffsetFor(
     const LayoutObject& layout_object) const {
-  DCHECK_EQ(items_.size(), offsets_.size());
-  for (const scoped_refptr<const NGFragmentItem>& item : items_) {
+  for (const ItemWithOffset& item : items_) {
     if (item->GetLayoutObject() == &layout_object)
-      return offsets_[&item - items_.begin()];
+      return item.offset;
   }
   return base::nullopt;
 }

third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.h

@@ -67,6 +67,26 @@ class CORE_EXPORT NGFragmentItemsBuilder {
                 TextDirection direction,
                 const PhysicalSize& container_size);
 
+  struct ItemWithOffset {
+    DISALLOW_NEW();
+
+   public:
+    ItemWithOffset(scoped_refptr<const NGFragmentItem> item,
+                   const LogicalOffset& offset)
+        : item(std::move(item)), offset(offset) {}
+    explicit ItemWithOffset(const LogicalOffset& offset) : offset(offset) {}
+
+    const NGFragmentItem& operator*() const { return *item; }
+    const NGFragmentItem* operator->() const { return item.get(); }
+
+    scoped_refptr<const NGFragmentItem> item;
+    LogicalOffset offset;
+  };
+
+  // Give an inline size, the allocation of this vector is hot. "128" is
+  // heuristic. Usually 10-40, some wikipedia pages have >64 items.
+  using ItemWithOffsetList = Vector<ItemWithOffset, 128>;
+
   // Find |LogicalOffset| of the first |NGFragmentItem| for |LayoutObject|.
   base::Optional<LogicalOffset> LogicalOffsetFor(const LayoutObject&) const;
 
@@ -75,8 +95,9 @@ class CORE_EXPORT NGFragmentItemsBuilder {
   // containing block geometry for OOF-positioned nodes.
   //
   // Once this method has been called, new items cannot be added.
-  const Vector<scoped_refptr<const NGFragmentItem>>&
-  Items(WritingMode, TextDirection, const PhysicalSize& outer_size);
+  const ItemWithOffsetList& Items(WritingMode,
+                                  TextDirection,
+                                  const PhysicalSize& outer_size);
 
   // Build a |NGFragmentItems|. The builder cannot build twice because data set
   // to this builder may be cleared.
@@ -92,8 +113,7 @@ class CORE_EXPORT NGFragmentItemsBuilder {
                          TextDirection direction,
                          const PhysicalSize& outer_size);
 
-  Vector<scoped_refptr<const NGFragmentItem>> items_;
-  Vector<LogicalOffset> offsets_;
+  ItemWithOffsetList items_;
   String text_content_;
   String first_line_text_content_;
 

third_party/blink/renderer/core/layout/ng/ng_box_fragment_builder.cc

@@ -77,8 +77,9 @@ void GatherInlineContainerFragmentsFromLinebox(
   }
 }
 
+template <class Items>
 void GatherInlineContainerFragmentsFromItems(
-    const NGFragmentItems::Span& items,
+    const Items& items,
     const PhysicalOffset& box_offset,
     NGBoxFragmentBuilder::InlineContainingBlockMap* inline_containing_block_map,
     HashMap<const LayoutObject*, LineBoxPair>* containing_linebox_map) {