Transition to std::unordered_set for buffer view tracking

Has the same guarantees of pointer stabilty while also being significantly faster in cases where a buffer has thousands of views. This is the case in RE4 and this change leads to an almost 1000% performance improvement in that game.

app/src/main/cpp/skyline/gpu/buffer.cpp

@@ -259,12 +259,9 @@ namespace skyline::gpu {
     }
 
     BufferView Buffer::GetView(vk::DeviceSize offset, vk::DeviceSize size, vk::Format format) {
-        for (auto &view : views)
-            if (view.offset == offset && view.size == size && view.format == format)
-                return BufferView{shared_from_this(), &view};
-
-        views.emplace_back(offset, size, format);
-        return BufferView{shared_from_this(), &views.back()};
+        // Will return an iterator to the inserted view or the already-existing view if the same view is already in the set
+        auto it{views.emplace(offset, size, format).first};
+        return BufferView{shared_from_this(), &(*it)};
     }
 
     vk::DeviceSize Buffer::AcquireMegaBuffer(MegaBuffer& megaBuffer) {
@@ -295,7 +292,7 @@ namespace skyline::gpu {
 
     Buffer::BufferViewStorage::BufferViewStorage(vk::DeviceSize offset, vk::DeviceSize size, vk::Format format) : offset(offset), size(size), format(format) {}
 
-    Buffer::BufferDelegate::BufferDelegate(std::shared_ptr<Buffer> pBuffer, Buffer::BufferViewStorage *view) : buffer(std::move(pBuffer)), view(view) {
+    Buffer::BufferDelegate::BufferDelegate(std::shared_ptr<Buffer> pBuffer, const Buffer::BufferViewStorage *view) : buffer(std::move(pBuffer)), view(view) {
         iterator = buffer->delegates.emplace(buffer->delegates.end(), this);
     }
 
@@ -339,7 +336,7 @@ namespace skyline::gpu {
         }
     }
 
-    BufferView::BufferView(std::shared_ptr<Buffer> buffer, Buffer::BufferViewStorage *view) : bufferDelegate(std::make_shared<Buffer::BufferDelegate>(std::move(buffer), view)) {}
+    BufferView::BufferView(std::shared_ptr<Buffer> buffer, const Buffer::BufferViewStorage *view) : bufferDelegate(std::make_shared<Buffer::BufferDelegate>(std::move(buffer), view)) {}
 
     void BufferView::AttachCycle(const std::shared_ptr<FenceCycle> &cycle) {
         auto buffer{bufferDelegate->buffer.get()};

app/src/main/cpp/skyline/gpu/buffer.h

@@ -3,6 +3,8 @@
 
 #pragma once
 
+#include <unordered_set>
+#include <boost/functional/hash.hpp>
 #include <nce.h>
 #include "memory_manager.h"
 
@@ -53,10 +55,26 @@ namespace skyline::gpu {
             vk::Format format;
 
             BufferViewStorage(vk::DeviceSize offset, vk::DeviceSize size, vk::Format format);
+
+            auto operator<=>(const BufferViewStorage &) const = default;
         };
 
       private:
-        std::list<BufferViewStorage> views; //!< BufferViewStorage(s) that are backed by this Buffer, used for storage and repointing to a new Buffer on deletion
+        /**
+         * @brief Hash function for BufferViewStorage to be used in the views set
+         */
+        struct BufferViewStorageHash {
+            size_t operator()(const BufferViewStorage &entry) const noexcept {
+                size_t seed{};
+                boost::hash_combine(seed, entry.offset);
+                boost::hash_combine(seed, entry.size);
+                boost::hash_combine(seed, entry.format);
+
+                return seed;
+            }
+        };
+
+        std::unordered_set<BufferViewStorage, BufferViewStorageHash> views; //!< BufferViewStorage(s) that are backed by this Buffer, used for storage and repointing to a new Buffer on deletion
 
       public:
         /**
@@ -65,11 +83,11 @@ namespace skyline::gpu {
          */
         struct BufferDelegate : public FenceCycleDependency {
             std::shared_ptr<Buffer> buffer;
-            Buffer::BufferViewStorage *view;
+            const Buffer::BufferViewStorage *view;
             std::function<void(const BufferViewStorage &, const std::shared_ptr<Buffer> &)> usageCallback;
             std::list<BufferDelegate *>::iterator iterator;
 
-            BufferDelegate(std::shared_ptr<Buffer> buffer, Buffer::BufferViewStorage *view);
+            BufferDelegate(std::shared_ptr<Buffer> buffer, const Buffer::BufferViewStorage *view);
 
             ~BufferDelegate();
 
@@ -262,7 +280,7 @@ namespace skyline::gpu {
     struct BufferView {
         std::shared_ptr<Buffer::BufferDelegate> bufferDelegate;
 
-        BufferView(std::shared_ptr<Buffer> buffer, Buffer::BufferViewStorage *view);
+        BufferView(std::shared_ptr<Buffer> buffer, const Buffer::BufferViewStorage *view);
 
         constexpr BufferView(nullptr_t = nullptr) : bufferDelegate(nullptr) {}
 

app/src/main/cpp/skyline/gpu/buffer_manager.cpp

@@ -55,13 +55,19 @@ namespace skyline::gpu {
 
             buffers.erase(std::find(buffers.begin(), buffers.end(), overlap));
 
-            // Transfer all views from the overlapping buffer to the new buffer with the new buffer and updated offset
+            // Transfer all views from the overlapping buffer to the new buffer with the new buffer and updated offset, ensuring pointer stability
             vk::DeviceSize overlapOffset{static_cast<vk::DeviceSize>(overlap->guest->begin() - newBuffer->guest->begin())};
-            if (overlapOffset != 0)
-                for (auto &view : overlap->views)
-                    view.offset += overlapOffset;
+            if (overlapOffset != 0) {
+                // This is a slight hack as we really shouldn't be changing the underlying set elements without a rehash but without writing our own set impl this is the best we can do
+                for (auto it{overlap->views.begin()}; it != overlap->views.end(); it++)
+                    const_cast<Buffer::BufferViewStorage *>(&*it)->offset += overlapOffset;
 
-            newBuffer->views.splice(newBuffer->views.end(), overlap->views);
+                // All current hashes are invalidated by above loop so rehash the container
+                overlap->views.rehash(0);
+            }
+
+            // Merge the view sets, this will keep pointer stability hence avoiding any reallocation
+            newBuffer->views.merge(overlap->views);
 
             // Transfer all delegates references from the overlapping buffer to the new buffer
             for (auto &delegate : overlap->delegates) {