[Impeller] combine uniform metadata and buffer slots. (flutter#45021)

Follow up from flutter#44990

We're spending a ton of time deallocating mostly empty maps, by reducing the number of maps we reduce the amount of memory used, and reduce map lookups.

Author: Jonah Williams

impeller/renderer/backend/gles/buffer_bindings_gles.cc

@@ -145,12 +145,12 @@ bool BufferBindingsGLES::BindUniformData(
     const Bindings& vertex_bindings,
     const Bindings& fragment_bindings) const {
   for (const auto& buffer : vertex_bindings.buffers) {
-    if (!BindUniformBuffer(gl, transients_allocator, buffer.second)) {
+    if (!BindUniformBuffer(gl, transients_allocator, buffer.second.view)) {
       return false;
     }
   }
   for (const auto& buffer : fragment_bindings.buffers) {
-    if (!BindUniformBuffer(gl, transients_allocator, buffer.second)) {
+    if (!BindUniformBuffer(gl, transients_allocator, buffer.second.view)) {
       return false;
     }
   }

impeller/renderer/backend/metal/compute_pass_mtl.mm

@@ -225,7 +225,7 @@ static bool Bind(ComputePassBindingsCache& pass,
 
     for (const auto& buffer : command.bindings.buffers) {
       if (!Bind(pass_bindings, *allocator, buffer.first,
-                buffer.second.resource)) {
+                buffer.second.view.resource)) {
         return false;
       }
     }

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -409,7 +409,7 @@ static bool Bind(PassBindingsCache& pass,
                                   ShaderStage stage) -> bool {
     for (const auto& buffer : bindings.buffers) {
       if (!Bind(pass_bindings, *allocator, stage, buffer.first,
-                buffer.second.resource)) {
+                buffer.second.view.resource)) {
         return false;
       }
     }

impeller/renderer/backend/vulkan/compute_pass_vk.cc

@@ -125,8 +125,8 @@ static bool AllocateAndBindDescriptorSets(const ContextVK& context,
                        &desc_set,    //
                        &vk_desc_set  //
   ](const Bindings& bindings) -> bool {
-    for (const auto& [buffer_index, view] : bindings.buffers) {
-      const auto& buffer_view = view.resource.buffer;
+    for (const auto& [buffer_index, data] : bindings.buffers) {
+      const auto& buffer_view = data.view.resource.buffer;
 
       auto device_buffer = buffer_view->GetDeviceBuffer(allocator);
       if (!device_buffer) {
@@ -143,14 +143,14 @@ static bool AllocateAndBindDescriptorSets(const ContextVK& context,
         return false;
       }
 
-      uint32_t offset = view.resource.range.offset;
+      uint32_t offset = data.view.resource.range.offset;
 
       vk::DescriptorBufferInfo buffer_info;
       buffer_info.buffer = buffer;
       buffer_info.offset = offset;
-      buffer_info.range = view.resource.range.length;
+      buffer_info.range = data.view.resource.range.length;
 
-      const ShaderUniformSlot& uniform = bindings.uniforms.at(buffer_index);
+      const ShaderUniformSlot& uniform = data.slot;
       auto layout_it = std::find_if(desc_set.begin(), desc_set.end(),
                                     [&uniform](DescriptorSetLayout& layout) {
                                       return layout.binding == uniform.binding;

impeller/renderer/backend/vulkan/render_pass_vk.cc

@@ -368,8 +368,8 @@ static bool AllocateAndBindDescriptorSets(const ContextVK& context,
                        &desc_set,    //
                        &vk_desc_set  //
   ](const Bindings& bindings) -> bool {
-    for (const auto& [buffer_index, view] : bindings.buffers) {
-      const auto& buffer_view = view.resource.buffer;
+    for (const auto& [buffer_index, data] : bindings.buffers) {
+      const auto& buffer_view = data.view.resource.buffer;
 
       auto device_buffer = buffer_view->GetDeviceBuffer(allocator);
       if (!device_buffer) {
@@ -391,14 +391,14 @@ static bool AllocateAndBindDescriptorSets(const ContextVK& context,
         return false;
       }
 
-      uint32_t offset = view.resource.range.offset;
+      uint32_t offset = data.view.resource.range.offset;
 
       vk::DescriptorBufferInfo buffer_info;
       buffer_info.buffer = buffer;
       buffer_info.offset = offset;
-      buffer_info.range = view.resource.range.length;
+      buffer_info.range = data.view.resource.range.length;
 
-      const ShaderUniformSlot& uniform = bindings.uniforms.at(buffer_index);
+      const ShaderUniformSlot& uniform = data.slot;
       auto layout_it = std::find_if(desc_set.begin(), desc_set.end(),
                                     [&uniform](DescriptorSetLayout& layout) {
                                       return layout.binding == uniform.binding;

impeller/renderer/command.cc

@@ -18,8 +18,8 @@ bool Command::BindVertices(const VertexBuffer& buffer) {
     return false;
   }
 
-  vertex_bindings.buffers[VertexDescriptor::kReservedVertexBufferIndex] = {
-      nullptr, buffer.vertex_buffer};
+  vertex_bindings.buffers[VertexDescriptor::kReservedVertexBufferIndex] =
+      BufferAndUniformSlot{.slot = {}, .view = {nullptr, buffer.vertex_buffer}};
   index_buffer = buffer.index_buffer;
   vertex_count = buffer.vertex_count;
   index_type = buffer.index_type;
@@ -30,7 +30,7 @@ BufferView Command::GetVertexBuffer() const {
   auto found = vertex_bindings.buffers.find(
       VertexDescriptor::kReservedVertexBufferIndex);
   if (found != vertex_bindings.buffers.end()) {
-    return found->second.resource;
+    return found->second.view.resource;
   }
   return {};
 }
@@ -61,13 +61,12 @@ bool Command::DoBindResource(ShaderStage stage,
 
   switch (stage) {
     case ShaderStage::kVertex:
-      vertex_bindings.uniforms[slot.ext_res_0] = slot;
-      vertex_bindings.buffers[slot.ext_res_0] = BufferResource(metadata, view);
+      vertex_bindings.buffers[slot.ext_res_0] = {
+          .slot = slot, .view = BufferResource(metadata, view)};
       return true;
     case ShaderStage::kFragment:
-      fragment_bindings.uniforms[slot.ext_res_0] = slot;
-      fragment_bindings.buffers[slot.ext_res_0] =
-          BufferResource(metadata, view);
+      fragment_bindings.buffers[slot.ext_res_0] = {
+          .slot = slot, .view = BufferResource(metadata, view)};
       return true;
     case ShaderStage::kCompute:
       VALIDATION_LOG << "Use ComputeCommands for compute shader stages.";

impeller/renderer/command.h

@@ -68,10 +68,15 @@ struct TextureAndSampler {
   SamplerResource sampler;
 };
 
+/// @brief combines the buffer resource and its uniform slot information.
+struct BufferAndUniformSlot {
+  ShaderUniformSlot slot;
+  BufferResource view;
+};
+
 struct Bindings {
-  std::map<size_t, ShaderUniformSlot> uniforms;
   std::map<size_t, TextureAndSampler> sampled_images;
-  std::map<size_t, BufferResource> buffers;
+  std::map<size_t, BufferAndUniformSlot> buffers;
 };
 
 //------------------------------------------------------------------------------

impeller/renderer/compute_command.cc

@@ -23,8 +23,7 @@ bool ComputeCommand::BindResource(ShaderStage stage,
     return false;
   }
 
-  bindings.uniforms[slot.ext_res_0] = slot;
-  bindings.buffers[slot.ext_res_0] = {&metadata, view};
+  bindings.buffers[slot.ext_res_0] = {.slot = slot, .view = {&metadata, view}};
   return true;
 }