Reduce allocations during beatmap selection

osu.Game.Rulesets.Osu/Difficulty/Preprocessing/OsuDifficultyHitObject.cs

@@ -232,7 +232,13 @@ namespace osu.Game.Rulesets.Osu.Difficulty.Preprocessing
 
             IList<HitObject> nestedObjects = slider.NestedHitObjects;
 
-            SliderTick? lastRealTick = slider.NestedHitObjects.OfType<SliderTick>().LastOrDefault();
+            SliderTick? lastRealTick = null;
+
+            foreach (var hitobject in slider.NestedHitObjects)
+            {
+                if (hitobject is SliderTick tick)
+                    lastRealTick = tick;
+            }
 
             if (lastRealTick?.StartTime > trackingEndTime)
             {

osu.Game.Rulesets.Osu/Objects/OsuHitObject.cs

@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using System.Linq;
 using osu.Framework.Bindables;
 using osu.Game.Beatmaps;
 using osu.Game.Beatmaps.ControlPoints;
@@ -149,8 +148,11 @@ namespace osu.Game.Rulesets.Osu.Objects
         {
             StackHeightBindable.BindValueChanged(height =>
             {
-                foreach (var nested in NestedHitObjects.OfType<OsuHitObject>())
+                foreach (var nested in NestedHitObjects)
-                    nested.StackHeight = height.NewValue;
+                {
+                    if (nested is OsuHitObject osuHitObject)
+                        osuHitObject.StackHeight = height.NewValue;
+                }
             });
         }
 

osu.Game.Rulesets.Osu/Objects/Slider.cs

@@ -252,18 +252,42 @@ namespace osu.Game.Rulesets.Osu.Objects
 
         protected void UpdateNestedSamples()
         {
-            var firstSample = Samples.FirstOrDefault(s => s.Name == HitSampleInfo.HIT_NORMAL)
+            HitSampleInfo firstSample = null;
-                              ?? Samples.FirstOrDefault(); // TODO: remove this when guaranteed sort is present for samples (https://github.com/ppy/osu/issues/1933)
+
+            for (int i = 0; i < Samples.Count; i++)
+            {
+                // TODO: remove this when guaranteed sort is present for samples (https://github.com/ppy/osu/issues/1933)
+                if (i == 0)
+                {
+                    firstSample = Samples[i];
+                    continue;
+                }
+
+                if (Samples[i].Name != HitSampleInfo.HIT_NORMAL)
+                    continue;
+
+                firstSample = Samples[i];
+                break;
+            }
+
             var sampleList = new List<HitSampleInfo>();
 
             if (firstSample != null)
                 sampleList.Add(firstSample.With("slidertick"));
 
-            foreach (var tick in NestedHitObjects.OfType<SliderTick>())
+            foreach (var nested in NestedHitObjects)
-                tick.Samples = sampleList;
+            {
+                switch (nested)
+                {
+                    case SliderTick tick:
+                        tick.Samples = sampleList;
+                        break;
 
-            foreach (var repeat in NestedHitObjects.OfType<SliderRepeat>())
+                    case SliderRepeat repeat:
-                repeat.Samples = this.GetNodeSamples(repeat.RepeatIndex + 1);
+                        repeat.Samples = this.GetNodeSamples(repeat.RepeatIndex + 1);
+                        break;
+                }
+            }
 
             if (HeadCircle != null)
                 HeadCircle.Samples = this.GetNodeSamples(0);

osu.Game/Rulesets/Objects/SliderPath.cs

@@ -61,16 +61,17 @@ namespace osu.Game.Rulesets.Objects
                     case NotifyCollectionChangedAction.Add:
                         Debug.Assert(args.NewItems != null);
 
-                        foreach (var c in args.NewItems.Cast<PathControlPoint>())
+                        foreach (object? newItem in args.NewItems)
-                            c.Changed += invalidate;
+                            ((PathControlPoint)newItem).Changed += invalidate;
+
                         break;
 
                     case NotifyCollectionChangedAction.Reset:
                     case NotifyCollectionChangedAction.Remove:
                         Debug.Assert(args.OldItems != null);
 
-                        foreach (var c in args.OldItems.Cast<PathControlPoint>())
+                        foreach (object? oldItem in args.OldItems)
-                            c.Changed -= invalidate;
+                            ((PathControlPoint)oldItem).Changed -= invalidate;
                         break;
                 }
 
@@ -269,10 +270,10 @@ namespace osu.Game.Rulesets.Objects
                 {
                     List<Vector2> subPath = calculateSubPath(segmentVertices, segmentType);
                     // Skip the first vertex if it is the same as the last vertex from the previous segment
-                    int skipFirst = calculatedPath.Count > 0 && subPath.Count > 0 && calculatedPath.Last() == subPath[0] ? 1 : 0;
+                    bool skipFirst = calculatedPath.Count > 0 && subPath.Count > 0 && calculatedPath.Last() == subPath[0];
 
-                    foreach (Vector2 t in subPath.Skip(skipFirst))
+                    for (int j = skipFirst ? 1 : 0; j < subPath.Count; j++)
-                        calculatedPath.Add(t);
+                        calculatedPath.Add(subPath[j]);
                 }
 
                 if (i > 0)

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -510,12 +510,27 @@ namespace osu.Game.Screens.Select
             if (beatmapInfo?.Hidden != false)
                 return false;
 
-            foreach (CarouselBeatmapSet set in beatmapSets)
+            foreach (var carouselItem in root.Items)
             {
+                if (carouselItem is not CarouselBeatmapSet set)
+                    continue;
+
                 if (!bypassFilters && set.Filtered.Value)
                     continue;
 
-                var item = set.Beatmaps.FirstOrDefault(p => p.BeatmapInfo.Equals(beatmapInfo));
+                CarouselBeatmap? item = null;
+
+                foreach (var setCarouselItem in set.Items)
+                {
+                    if (setCarouselItem is not CarouselBeatmap setCarouselBeatmap)
+                        continue;
+
+                    if (!setCarouselBeatmap.BeatmapInfo.Equals(beatmapInfo))
+                        continue;
+
+                    item = setCarouselBeatmap;
+                    break;
+                }
 
                 if (item == null)
                     // The beatmap that needs to be selected doesn't exist in this set