Auto merge of #3374 - kvark:rt-alloc, r=gw3583

Extend the scope of render target allocation strategy acrosss layers

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1509672

Technically consists of 3 parts:
  - cleanup bits, don't affect performance
  - spread the dynamic target allocation bins across the layers. Previously, we had each layer with it's own allocator, and we were only ever trying to allocate from the last one. This scheme was weak against cases where we reach the ideal maximum target size, since guillotine allocation of small bits forced us to spawn more and more layers... reaching almost 150 in the target case. New scheme uses the layers more efficiently, reducing the layers to just 3 (.. 50x reduction :P). Pending [try push](https://treeherder.mozilla.org/#/jobs?repo=try&revision=27464c7d62f0f05a0bc96a7133b55e9706d3d449).
  - when we reach the ideal max size, also round up the requested size to 256. This makes allocations *within a layer* to be more robust against small inputs. With this change, the number of layers drops to just 2 (.. 75x reduction lol), which appears to be minimal for this case. Pending [try push](https://treeherder.mozilla.org/#/jobs?repo=try&revision=1f4593fd68455842a7b12f396d0abbdf887a11a0).

The page scrolls smoothly with those changes, on my GTX TI 1050 at least.

r? @gw3583

Note: the bugzilla issue also suffers from poor batching, I'm going to look at it separately.

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appveyor.yml

@@ -8,8 +8,8 @@ environment:
   TARGET: x86_64-pc-windows-msvc
 
 install:
-  - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-1.27.0-${env:TARGET}.msi"
-  - msiexec /passive /i "rust-1.27.0-%TARGET%.msi" ADDLOCAL=Rustc,Cargo,Std INSTALLDIR=C:\Rust
+  - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-1.30.0-${env:TARGET}.msi"
+  - msiexec /passive /i "rust-1.30.0-%TARGET%.msi" ADDLOCAL=Rustc,Cargo,Std INSTALLDIR=C:\Rust
   - rustc -V
   - cargo -V
 

webrender/Cargo.toml

@@ -68,6 +68,7 @@ optional = true
 
 [dev-dependencies]
 mozangle = "0.1"
+rand = "0.4"
 
 [target.'cfg(any(target_os = "android", all(unix, not(target_os = "macos"))))'.dependencies]
 freetype = { version = "0.4", default-features = false }

webrender/src/batch.rs

@@ -151,7 +151,8 @@ impl AlphaBatchList {
     ) -> &mut Vec<PrimitiveInstanceData> {
         if z_id != self.current_z_id ||
            self.current_batch_index == usize::MAX ||
-           !self.batches[self.current_batch_index].key.is_compatible_with(&key) {
+           !self.batches[self.current_batch_index].key.is_compatible_with(&key)
+        {
             let mut selected_batch_index = None;
 
             match key.blend_mode {

webrender/src/lib.rs

@@ -190,6 +190,8 @@ extern crate image as image_loader;
 extern crate base64;
 #[cfg(all(feature = "capture", feature = "png"))]
 extern crate png;
+#[cfg(test)]
+extern crate rand;
 
 pub extern crate webrender_api;
 

webrender/src/render_task.rs

@@ -144,8 +144,12 @@ impl RenderTaskTree {
             pass_index
         };
 
-        let pass = &mut passes[pass_index];
-        pass.add_render_task(id, task.get_dynamic_size(), task.target_kind(), &task.location);
+        passes[pass_index].add_render_task(
+            id,
+            task.get_dynamic_size(),
+            task.target_kind(),
+            &task.location,
+        );
     }
 
     pub fn prepare_for_render(&mut self) {