Bug 1642629 - Preallocate CompositeStateDescriptor vectors. r=kvark

Vector reallocations in CompositeState::push_surface are taking about 2% of total frame building time before this patch. There was an effort at preallocating some with constant values but I suspect these constants haven't been updated along with picture cachign heuristics.

Differential Revision: https://phabricator.services.mozilla.com/D80195

gfx/wr/webrender/src/composite.rs

@@ -13,6 +13,7 @@ use crate::picture::{ImageDependency, ResolvedSurfaceTexture, TileCacheInstance,
 use crate::prim_store::DeferredResolve;
 use crate::renderer::ImageBufferKind;
 use crate::resource_cache::{ImageRequest, ResourceCache};
+use crate::util::Preallocator;
 use std::{ops, u64};
 
 /*
@@ -340,7 +341,49 @@ impl CompositeDescriptor {
     /// Construct an empty descriptor.
     pub fn empty() -> Self {
         CompositeDescriptor {
-            surfaces: Vec::with_capacity(8),
+            surfaces: Vec::new(),
+        }
+    }
+}
+
+pub struct CompositeStatePreallocator {
+    opaque_tiles: Preallocator,
+    alpha_tiles: Preallocator,
+    clear_tiles: Preallocator,
+    external_surfaces: Preallocator,
+    occluders: Preallocator,
+    descriptor_surfaces: Preallocator,
+}
+
+impl CompositeStatePreallocator {
+    pub fn record(&mut self, state: &CompositeState) {
+        self.opaque_tiles.record_vec(&state.opaque_tiles);
+        self.alpha_tiles.record_vec(&state.alpha_tiles);
+        self.clear_tiles.record_vec(&state.clear_tiles);
+        self.external_surfaces.record_vec(&state.external_surfaces);
+        self.occluders.record_vec(&state.occluders);
+        self.descriptor_surfaces.record_vec(&state.descriptor.surfaces);
+    }
+
+    pub fn preallocate(&self, state: &mut CompositeState) {
+        self.opaque_tiles.preallocate_vec(&mut state.opaque_tiles);
+        self.alpha_tiles.preallocate_vec(&mut state.alpha_tiles);
+        self.clear_tiles.preallocate_vec(&mut state.clear_tiles);
+        self.external_surfaces.preallocate_vec(&mut state.external_surfaces);
+        self.occluders.preallocate_vec(&mut state.occluders);
+        self.descriptor_surfaces.preallocate_vec(&mut state.descriptor.surfaces);
+    }
+}
+
+impl Default for CompositeStatePreallocator {
+    fn default() -> Self {
+        CompositeStatePreallocator {
+            opaque_tiles: Preallocator::new(40),
+            alpha_tiles: Preallocator::new(16),
+            clear_tiles: Preallocator::new(0),
+            external_surfaces: Preallocator::new(0),
+            occluders: Preallocator::new(16),
+            descriptor_surfaces: Preallocator::new(8),
         }
     }
 }
@@ -400,15 +443,15 @@ impl CompositeState {
         }
 
         CompositeState {
-            opaque_tiles: Vec::with_capacity(40),
-            alpha_tiles: Vec::with_capacity(16),
+            opaque_tiles: Vec::new(),
+            alpha_tiles: Vec::new(),
             clear_tiles: Vec::new(),
             z_generator: ZBufferIdGenerator::new(0, max_depth_ids),
             dirty_rects_are_valid: true,
             compositor_kind,
             picture_caching_is_enabled,
             global_device_pixel_scale,
-            occluders: Vec::with_capacity(16),
+            occluders: Vec::new(),
             descriptor: CompositeDescriptor::empty(),
             external_surfaces: Vec::new(),
         }

gfx/wr/webrender/src/frame_builder.rs

@@ -7,7 +7,7 @@ use api::units::*;
 use crate::batch::{BatchBuilder, AlphaBatchBuilder, AlphaBatchContainer};
 use crate::clip::{ClipStore, ClipChainStack};
 use crate::spatial_tree::{SpatialTree, ROOT_SPATIAL_NODE_INDEX, SpatialNodeIndex};
-use crate::composite::{CompositorKind, CompositeState};
+use crate::composite::{CompositorKind, CompositeState, CompositeStatePreallocator};
 use crate::debug_render::DebugItem;
 use crate::gpu_cache::{GpuCache, GpuCacheHandle};
 use crate::gpu_types::{PrimitiveHeaders, TransformPalette, UvRectKind, ZBufferIdGenerator};
@@ -163,6 +163,8 @@ pub struct FrameBuilder {
     pub globals: FrameGlobalResources,
     #[cfg_attr(feature = "capture", serde(skip))]
     prim_headers_prealloc: Preallocator,
+    #[cfg_attr(feature = "capture", serde(skip))]
+    composite_state_prealloc: CompositeStatePreallocator,
 }
 
 pub struct FrameBuildingContext<'a> {
@@ -236,7 +238,8 @@ impl FrameBuilder {
         FrameBuilder {
             pending_retained_tiles: RetainedTiles::new(),
             globals: FrameGlobalResources::empty(),
-            prim_headers_prealloc: Preallocator::new(0)
+            prim_headers_prealloc: Preallocator::new(0),
+            composite_state_prealloc: CompositeStatePreallocator::default(),
         }
     }
 
@@ -582,6 +585,8 @@ impl FrameBuilder {
             scene.config.max_depth_ids,
         );
 
+        self.composite_state_prealloc.preallocate(&mut composite_state);
+
         let main_render_task_id = self.build_layer_screen_rects_and_cull_layers(
             scene,
             screen_world_rect,
@@ -672,6 +677,7 @@ impl FrameBuilder {
         resource_cache.end_frame(&mut resource_profile.texture_cache);
 
         self.prim_headers_prealloc.record_vec(&mut prim_headers.headers_int);
+        self.composite_state_prealloc.record(&composite_state);
 
         Frame {
             content_origin: scene.output_rect.origin,