Move NGLogicalLineItems to NGInlineChildLayoutContext

This patch moves the ownership of |NGLogicalLineItems| from
|NGInlineLayoutAlgorithm| to |NGInlineChildLayoutContext|.

This change:
* Avoids moving |NGLogicalLineItems| to |NGFragmentItemsBuilder|.
  |NGLogicalLineItems| has an inline size that moving is more
  expensive than regular |Vector|.
* Can reuse the buffer (if expanded) for the next line.

Also, when clearing |NGLogicalLineItems|, make sure it
doesn't release the allocated buffer.

Bug: 982194
Change-Id: I8fa2416769618823876cd2a2669208e60623faeb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2259755
Commit-Queue: Koji Ishii <kojii@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781269}

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

@@ -38,11 +38,13 @@ NGFragmentItemsBuilder::NGFragmentItemsBuilder(
 
 void NGFragmentItemsBuilder::SetCurrentLine(
     const NGPhysicalLineBoxFragment& line,
-    NGLogicalLineItems&& children) {
+    NGLogicalLineItems* current_line) {
 #if DCHECK_IS_ON()
   current_line_fragment_ = &line;
 #endif
-  current_line_ = std::move(children);
+  DCHECK(!current_line_);
+  DCHECK(current_line);
+  current_line_ = current_line;
 }
 
 void NGFragmentItemsBuilder::AddLine(const NGPhysicalLineBoxFragment& line,
@@ -51,10 +53,11 @@ void NGFragmentItemsBuilder::AddLine(const NGPhysicalLineBoxFragment& line,
 #if DCHECK_IS_ON()
   DCHECK_EQ(current_line_fragment_, &line);
 #endif
+  DCHECK(current_line_);
 
   // Reserve the capacity for (children + line box item).
   const wtf_size_t size_before = items_.size();
-  const wtf_size_t estimated_size = size_before + current_line_.size() + 1;
+  const wtf_size_t estimated_size = size_before + current_line_->size() + 1;
   const wtf_size_t old_capacity = items_.capacity();
   if (estimated_size > old_capacity)
     items_.ReserveCapacity(std::max(estimated_size, old_capacity * 2));
@@ -63,7 +66,7 @@ void NGFragmentItemsBuilder::AddLine(const NGPhysicalLineBoxFragment& line,
   const wtf_size_t line_start_index = items_.size();
   items_.emplace_back(offset, line);
 
-  AddItems(current_line_.begin(), current_line_.end());
+  AddItems(current_line_->begin(), current_line_->end());
 
   // All children are added. Create an item for the start of the line.
   NGFragmentItem& line_item = items_[line_start_index].item;
@@ -74,8 +77,11 @@ void NGFragmentItemsBuilder::AddLine(const NGPhysicalLineBoxFragment& line,
   // Keep children's offsets relative to |line|. They will be adjusted later in
   // |ConvertToPhysical()|.
 
-  current_line_.clear();
+  // Clear the current line without releasing the buffer. It is likely to be
+  // reused again.
+  current_line_->Shrink(0);
 #if DCHECK_IS_ON()
+  current_line_ = nullptr;
   current_line_fragment_ = nullptr;
 #endif
 

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

@@ -57,10 +57,9 @@ class CORE_EXPORT NGFragmentItemsBuilder {
   // positions the line box. |SetCurrentLine| sets the children, and the next
   // |AddLine| adds them.
   //
-  // TODO(kojii): Moving |NGLogicalLineItems| is not cheap because it has inline
-  // capacity. Reconsider the ownership.
+  // The caller must keep |children| alive until |AddLine| completes.
   void SetCurrentLine(const NGPhysicalLineBoxFragment& line,
-                      NGLogicalLineItems&& children);
+                      NGLogicalLineItems* current_line);
   void AddLine(const NGPhysicalLineBoxFragment& line,
                const LogicalOffset& offset);
 
@@ -131,7 +130,7 @@ class CORE_EXPORT NGFragmentItemsBuilder {
   String first_line_text_content_;
 
   // Keeps children of a line until the offset is determined. See |AddLine|.
-  NGLogicalLineItems current_line_;
+  NGLogicalLineItems* current_line_ = nullptr;
 
   NGInlineNode node_;
 

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

@@ -9,6 +9,7 @@ namespace blink {
 namespace {
 
 struct SameSizeAsNGInlineChildLayoutContext {
+  NGLogicalLineItems line_items_;
   base::Optional<NGInlineLayoutStateStack> box_states_;
   void* pointers[2];
   unsigned number;

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

@@ -7,6 +7,7 @@
 
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_inline_box_state.h"
+#include "third_party/blink/renderer/core/layout/ng/inline/ng_logical_line_item.h"
 
 namespace blink {
 
@@ -27,6 +28,10 @@ class NGInlineChildLayoutContext {
     items_builder_ = builder;
   }
 
+  // Returns an instance of |NGLogicalLineItems|. This is reused when laying out
+  // the next line.
+  NGLogicalLineItems* LogicalLineItems() { return &logical_line_items_; }
+
   // Returns the NGInlineLayoutStateStack in this context.
   bool HasBoxStates() const { return box_states_.has_value(); }
   NGInlineLayoutStateStack* BoxStates() { return &*box_states_; }
@@ -50,6 +55,8 @@ class NGInlineChildLayoutContext {
   // transit, allocating separately is easier.
   NGFragmentItemsBuilder* items_builder_ = nullptr;
 
+  NGLogicalLineItems logical_line_items_;
+
   base::Optional<NGInlineLayoutStateStack> box_states_;
 
   // The items and its index this context is set up for.

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

@@ -64,12 +64,14 @@ NGInlineLayoutAlgorithm::NGInlineLayoutAlgorithm(
           // lays out in visual order.
           TextDirection::kLtr,
           break_token),
+      line_box_(*context->LogicalLineItems()),
       box_states_(nullptr),
       context_(context),
       baseline_type_(container_builder_.Style().GetFontBaseline()),
       is_horizontal_writing_mode_(
           blink::IsHorizontalWritingMode(space.GetWritingMode())) {
   DCHECK(context);
+  DCHECK(&line_box_);
   quirks_mode_ = inline_node.InLineHeightQuirksMode();
 }
 
@@ -195,7 +197,8 @@ void NGInlineLayoutAlgorithm::CreateLine(
     NGExclusionSpace* exclusion_space) {
   // Needs MutableResults to move ShapeResult out of the NGLineInfo.
   NGInlineItemResults* line_items = line_info->MutableResults();
-  line_box_.resize(0);
+  // Clear the current line without releasing the buffer.
+  line_box_.Shrink(0);
 
   // Apply justification before placing items, because it affects size/position
   // of items, which are needed to compute inline static positions.
@@ -1078,7 +1081,7 @@ scoped_refptr<const NGLayoutResult> NGInlineLayoutAlgorithm::Layout() {
         container_builder_.ToLineBoxFragment();
     items_builder->SetCurrentLine(
         To<NGPhysicalLineBoxFragment>(layout_result->PhysicalFragment()),
-        std::move(line_box_));
+        &line_box_);
     return layout_result;
   }
 

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

@@ -111,7 +111,7 @@ class CORE_EXPORT NGInlineLayoutAlgorithm final
                                 const NGExclusionSpace&,
                                 LayoutUnit line_height);
 
-  NGLogicalLineItems line_box_;
+  NGLogicalLineItems& line_box_;
   NGInlineLayoutStateStack* box_states_;
   NGInlineChildLayoutContext* context_;
 

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

@@ -241,8 +241,7 @@ class NGLogicalLineItems {
   void ReserveInitialCapacity(unsigned capacity) {
     children_.ReserveInitialCapacity(capacity);
   }
-  void clear() { children_.resize(0); }
-  void resize(wtf_size_t size) { children_.resize(size); }
+  void Shrink(wtf_size_t size) { children_.Shrink(size); }
 
   using iterator = Vector<NGLogicalLineItem, 16>::iterator;
   iterator begin() { return children_.begin(); }