buffer_cache: Use boost::container::small_vector for maps in range

Most overlaps in the buffer cache only contain one mapped address.
We can avoid close to all heap allocations once the buffer cache is
warmed up by using a small_vector with a stack size of one.

src/video_core/buffer_cache/buffer_cache.h

@@ -12,6 +12,7 @@
 #include <utility>
 #include <vector>
 
+#include <boost/container/small_vector.hpp>
 #include <boost/icl/interval_map.hpp>
 #include <boost/icl/interval_set.hpp>
 #include <boost/intrusive/set.hpp>
@@ -33,6 +34,10 @@ namespace VideoCommon {
 
 template <typename OwnerBuffer, typename BufferType, typename StreamBuffer>
 class BufferCache {
+    using IntervalSet = boost::icl::interval_set<VAddr>;
+    using IntervalType = typename IntervalSet::interval_type;
+    using VectorMapInterval = boost::container::small_vector<MapInterval*, 1>;
+
 public:
     using BufferInfo = std::pair<BufferType, u64>;
 
@@ -133,7 +138,7 @@ public:
     void FlushRegion(VAddr addr, std::size_t size) {
         std::lock_guard lock{mutex};
 
-        std::vector<MapInterval*> objects = GetMapsInRange(addr, size);
+        VectorMapInterval objects = GetMapsInRange(addr, size);
         std::sort(objects.begin(), objects.end(),
                   [](MapInterval* lhs, MapInterval* rhs) { return lhs->ticks < rhs->ticks; });
         for (MapInterval* object : objects) {
@@ -148,7 +153,7 @@ public:
     bool MustFlushRegion(VAddr addr, std::size_t size) {
         std::lock_guard lock{mutex};
 
-        const std::vector<MapInterval*> objects = GetMapsInRange(addr, size);
+        const VectorMapInterval objects = GetMapsInRange(addr, size);
         return std::any_of(objects.cbegin(), objects.cend(), [](const MapInterval* map) {
             return map->is_modified && map->is_registered;
         });
@@ -158,8 +163,7 @@ public:
     void InvalidateRegion(VAddr addr, u64 size) {
         std::lock_guard lock{mutex};
 
-        std::vector<MapInterval*> objects = GetMapsInRange(addr, size);
-        for (auto& object : objects) {
+        for (auto& object : GetMapsInRange(addr, size)) {
             if (object->is_registered) {
                 Unregister(object);
             }
@@ -314,7 +318,7 @@ protected:
 private:
     MapInterval* MapAddress(const OwnerBuffer& block, GPUVAddr gpu_addr, VAddr cpu_addr,
                             std::size_t size) {
-        std::vector<MapInterval*> overlaps = GetMapsInRange(cpu_addr, size);
+        const VectorMapInterval overlaps = GetMapsInRange(cpu_addr, size);
         if (overlaps.empty()) {
             auto& memory_manager = system.GPU().MemoryManager();
             const VAddr cpu_addr_end = cpu_addr + size;
@@ -368,7 +372,7 @@ private:
     }
 
     void UpdateBlock(const OwnerBuffer& block, VAddr start, VAddr end,
-                     std::vector<MapInterval*>& overlaps) {
+                     const VectorMapInterval& overlaps) {
         const IntervalType base_interval{start, end};
         IntervalSet interval_set{};
         interval_set.add(base_interval);
@@ -387,14 +391,13 @@ private:
         }
     }
 
-    std::vector<MapInterval*> GetMapsInRange(VAddr addr, std::size_t size) {
+    VectorMapInterval GetMapsInRange(VAddr addr, std::size_t size) {
+        VectorMapInterval result;
         if (size == 0) {
-            return {};
+            return result;
         }
 
-        std::vector<MapInterval*> result;
         const VAddr addr_end = addr + size;
-
         auto it = mapped_addresses.lower_bound(addr);
         if (it != mapped_addresses.begin()) {
             --it;
@@ -574,10 +577,9 @@ private:
     u64 buffer_offset = 0;
     u64 buffer_offset_base = 0;
 
-    using IntervalSet = boost::icl::interval_set<VAddr>;
-    using IntervalType = typename IntervalSet::interval_type;
     std::list<MapInterval> mapped_addresses_storage; // Temporary hack
-    boost::intrusive::set<MapInterval, boost::intrusive::compare<MapIntervalCompare>> mapped_addresses;
+    boost::intrusive::set<MapInterval, boost::intrusive::compare<MapIntervalCompare>>
+        mapped_addresses;
 
     static constexpr u64 write_page_bit = 11;
     std::unordered_map<u64, u32> written_pages;