Auto merge of #3361 - kvark:push-item, r=jrmuizel

Introduce SerializedDisplayItem to reduce mem copies on DL construction

This PR addresses the part of #3358 about DL construction: instead of constructing the display items and associated data and passing through the serializer by value, we just pass the references around, which guarantees that no extra copies are made.

TODO:
- [x] verify that the copies are gone (need the tool hosted/opened somewhere)
- [x] Gecko try push with talos jobs

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Author: bors-servo

webrender_api/src/display_item.rs

@@ -66,6 +66,15 @@ pub struct GenericDisplayItem<T> {
 
 pub type DisplayItem = GenericDisplayItem<SpecificDisplayItem>;
 
+/// A modified version of DI where every field is borrowed instead of owned.
+/// It allows us to reduce copies during serialization.
+#[derive(Serialize)]
+pub struct SerializedDisplayItem<'a> {
+    pub item: &'a SpecificDisplayItem,
+    pub clip_and_scroll: &'a ClipAndScrollInfo,
+    pub info: &'a LayoutPrimitiveInfo,
+}
+
 #[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]
 pub struct PrimitiveInfo<T> {
     pub rect: TypedRect<f32, T>,

webrender_api/src/display_list.rs

@@ -23,8 +23,9 @@ use {ImageRendering, LayoutPoint, LayoutPrimitiveInfo, LayoutRect, LayoutSideOff
 use {LayoutTransform, LayoutVector2D, LineDisplayItem, LineOrientation, LineStyle, MixBlendMode};
 use {PipelineId, PropertyBinding, PushReferenceFrameDisplayListItem};
 use {PushStackingContextDisplayItem, RadialGradient, RadialGradientDisplayItem};
-use {RectangleDisplayItem, ReferenceFrame, ScrollFrameDisplayItem, ScrollSensitivity, Shadow};
-use {SpecificDisplayItem, StackingContext, StickyFrameDisplayItem, StickyOffsetBounds};
+use {RectangleDisplayItem, ReferenceFrame, ScrollFrameDisplayItem, ScrollSensitivity};
+use {SerializedDisplayItem, Shadow, SpecificDisplayItem};
+use {StackingContext, StickyFrameDisplayItem, StickyOffsetBounds};
 use {TextDisplayItem, TransformStyle, YuvColorSpace, YuvData, YuvImageDisplayItem, ColorDepth};
 
 // We don't want to push a long text-run. If a text-run is too long, split it into several parts.
@@ -691,16 +692,16 @@ impl<'a> Write for SizeCounter {
 /// If this assumption is incorrect, the result will be Undefined Behaviour. This
 /// assumption should hold for all derived Serialize impls, which is all we currently
 /// use.
-fn serialize_fast<T: Serialize>(vec: &mut Vec<u8>, e: &T) {
+fn serialize_fast<T: Serialize>(vec: &mut Vec<u8>, e: T) {
     // manually counting the size is faster than vec.reserve(bincode::serialized_size(&e) as usize) for some reason
     let mut size = SizeCounter(0);
-    bincode::serialize_into(&mut size, e).unwrap();
+    bincode::serialize_into(&mut size, &e).unwrap();
     vec.reserve(size.0);
 
     let old_len = vec.len();
     let ptr = unsafe { vec.as_mut_ptr().add(old_len) };
     let mut w = UnsafeVecWriter(ptr);
-    bincode::serialize_into(&mut w, e).unwrap();
+    bincode::serialize_into(&mut w, &e).unwrap();
 
     // fix up the length
     unsafe { vec.set_len(old_len + size.0); }
@@ -964,43 +965,36 @@ impl DisplayListBuilder {
     /// NOTE: It is usually preferable to use the specialized methods to push
     /// display items. Pushing unexpected or invalid items here may
     /// result in WebRender panicking or behaving in unexpected ways.
-    pub fn push_item(&mut self, item: SpecificDisplayItem, info: &LayoutPrimitiveInfo) {
+    pub fn push_item(&mut self, item: &SpecificDisplayItem, info: &LayoutPrimitiveInfo) {
         serialize_fast(
             &mut self.data,
-            &DisplayItem {
+            SerializedDisplayItem {
                 item,
-                clip_and_scroll: *self.clip_stack.last().unwrap(),
-                info: *info,
+                clip_and_scroll: self.clip_stack.last().unwrap(),
+                info,
             },
         )
     }
 
     fn push_item_with_clip_scroll_info(
         &mut self,
-        item: SpecificDisplayItem,
+        item: &SpecificDisplayItem,
         info: &LayoutPrimitiveInfo,
-        scrollinfo: ClipAndScrollInfo
+        clip_and_scroll: &ClipAndScrollInfo
     ) {
         serialize_fast(
             &mut self.data,
-            &DisplayItem {
+            SerializedDisplayItem {
                 item,
-                clip_and_scroll: scrollinfo,
-                info: *info,
+                clip_and_scroll,
+                info,
             },
         )
     }
 
-    fn push_new_empty_item(&mut self, item: SpecificDisplayItem, clip_and_scroll: &ClipAndScrollInfo) {
-        let info = LayoutPrimitiveInfo::new(LayoutRect::zero());
-        serialize_fast(
-            &mut self.data,
-            &DisplayItem {
-                item,
-                clip_and_scroll: *clip_and_scroll,
-                info,
-            }
-        )
+    fn push_new_empty_item(&mut self, item: &SpecificDisplayItem) {
+        let info = &LayoutPrimitiveInfo::new(LayoutRect::zero());
+        self.push_item(item, info)
     }
 
     fn push_iter_impl<I>(data: &mut Vec<u8>, iter_source: I)
@@ -1050,11 +1044,11 @@ impl DisplayListBuilder {
 
     pub fn push_rect(&mut self, info: &LayoutPrimitiveInfo, color: ColorF) {
         let item = SpecificDisplayItem::Rectangle(RectangleDisplayItem { color });
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     pub fn push_clear_rect(&mut self, info: &LayoutPrimitiveInfo) {
-        self.push_item(SpecificDisplayItem::ClearRectangle, info);
+        self.push_item(&SpecificDisplayItem::ClearRectangle, info);
     }
 
     pub fn push_line(
@@ -1072,7 +1066,7 @@ impl DisplayListBuilder {
             style,
         });
 
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     pub fn push_image(
@@ -1094,7 +1088,7 @@ impl DisplayListBuilder {
             color,
         });
 
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     /// Push a yuv image. All planar data in yuv image should use the same buffer type.
@@ -1112,7 +1106,7 @@ impl DisplayListBuilder {
             color_space,
             image_rendering,
         });
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     pub fn push_text(
@@ -1130,7 +1124,7 @@ impl DisplayListBuilder {
         });
 
         for split_glyphs in glyphs.chunks(MAX_TEXT_RUN_LENGTH) {
-            self.push_item(item, info);
+            self.push_item(&item, info);
             self.push_iter(split_glyphs);
         }
     }
@@ -1173,7 +1167,7 @@ impl DisplayListBuilder {
     ) {
         let item = SpecificDisplayItem::Border(BorderDisplayItem { details, widths });
 
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     pub fn push_box_shadow(
@@ -1197,7 +1191,7 @@ impl DisplayListBuilder {
             clip_mode,
         });
 
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     /// Pushes a linear gradient to be displayed.
@@ -1227,7 +1221,7 @@ impl DisplayListBuilder {
             tile_spacing,
         });
 
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     /// Pushes a radial gradient to be displayed.
@@ -1246,7 +1240,7 @@ impl DisplayListBuilder {
             tile_spacing,
         });
 
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     pub fn push_reference_frame(
@@ -1263,13 +1257,12 @@ impl DisplayListBuilder {
                 id,
             },
         });
-        self.push_item(item, info);
+        self.push_item(&item, info);
         id
     }
 
     pub fn pop_reference_frame(&mut self) {
-        let clip_and_scroll = *self.clip_stack.last().unwrap();
-        self.push_new_empty_item(SpecificDisplayItem::PopReferenceFrame, &clip_and_scroll);
+        self.push_new_empty_item(&SpecificDisplayItem::PopReferenceFrame);
     }
 
     pub fn push_stacking_context(
@@ -1290,21 +1283,19 @@ impl DisplayListBuilder {
             },
         });
 
-        self.push_item(item, info);
+        self.push_item(&item, info);
         self.push_iter(filters);
     }
 
     pub fn pop_stacking_context(&mut self) {
-        let clip_and_scroll = *self.clip_stack.last().unwrap();
-        self.push_new_empty_item(SpecificDisplayItem::PopStackingContext, &clip_and_scroll);
+        self.push_new_empty_item(&SpecificDisplayItem::PopStackingContext);
     }
 
     pub fn push_stops(&mut self, stops: &[GradientStop]) {
         if stops.is_empty() {
             return;
         }
-        let clip_and_scroll = *self.clip_stack.last().unwrap();
-        self.push_new_empty_item(SpecificDisplayItem::SetGradientStops, &clip_and_scroll);
+        self.push_new_empty_item(&SpecificDisplayItem::SetGradientStops);
         self.push_iter(stops);
     }
 
@@ -1372,9 +1363,9 @@ impl DisplayListBuilder {
         });
 
         self.push_item_with_clip_scroll_info(
-            item,
+            &item,
             &LayoutPrimitiveInfo::with_clip_rect(content_rect, clip_rect),
-            ClipAndScrollInfo::simple(parent),
+            &ClipAndScrollInfo::simple(parent),
         );
         self.push_iter(complex_clips);
 
@@ -1391,8 +1382,7 @@ impl DisplayListBuilder {
         I::IntoIter: ExactSizeIterator + Clone,
     {
         let id = self.generate_clip_chain_id();
-        let clip_and_scroll = *self.clip_stack.last().unwrap();
-        self.push_new_empty_item(SpecificDisplayItem::ClipChain(ClipChainItem { id, parent }), &clip_and_scroll);
+        self.push_new_empty_item(&SpecificDisplayItem::ClipChain(ClipChainItem { id, parent }));
         self.push_iter(clips);
         id
     }
@@ -1454,7 +1444,7 @@ impl DisplayListBuilder {
 
         let info = LayoutPrimitiveInfo::new(clip_rect);
 
-        self.push_item_with_clip_scroll_info(item, &info, scrollinfo);
+        self.push_item_with_clip_scroll_info(&item, &info, &scrollinfo);
         self.push_iter(complex_clips);
         id
     }
@@ -1477,7 +1467,7 @@ impl DisplayListBuilder {
         });
 
         let info = LayoutPrimitiveInfo::new(frame_rect);
-        self.push_item(item, &info);
+        self.push_item(&item, &info);
         id
     }
 
@@ -1509,24 +1499,21 @@ impl DisplayListBuilder {
             pipeline_id,
             ignore_missing_pipeline,
         });
-        self.push_item(item, info);
+        self.push_item(&item, info);
     }
 
     pub fn push_shadow(&mut self, info: &LayoutPrimitiveInfo, shadow: Shadow) {
-        self.push_item(SpecificDisplayItem::PushShadow(shadow), info);
+        self.push_item(&SpecificDisplayItem::PushShadow(shadow), info);
     }
 
     pub fn pop_all_shadows(&mut self) {
-        let clip_and_scroll = *self.clip_stack.last().unwrap();
-        self.push_new_empty_item(SpecificDisplayItem::PopAllShadows, &clip_and_scroll);
+        self.push_new_empty_item(&SpecificDisplayItem::PopAllShadows);
     }
 
     pub fn finalize(self) -> (PipelineId, LayoutSize, BuiltDisplayList) {
         assert!(self.save_state.is_none(), "Finalized DisplayListBuilder with a pending save");
 
         let end_time = precise_time_ns();
-
-
         (
             self.pipeline_id,
             self.content_size,