Added comments in performance sensitive code.

OpenRA.Game/Traits/Player/FrozenActorLayer.cs

@@ -86,10 +86,9 @@ namespace OpenRA.Traits
 		{
 			var wasVisible = Visible;
 			Shrouded = true;
-
-			// We are doing the following LINQ manually for performance since this is a hot path.
-			// Visible = !Footprint.Any(shroud.IsVisible);
 			Visible = true;
+
+			// PERF: Avoid LINQ.
 			foreach (var puv in Footprint)
 			{
 				if (shroud.IsVisible(puv))
@@ -142,7 +141,7 @@ namespace OpenRA.Traits
 
 		public bool ShouldBeRemoved(Player owner)
 		{
-			// We use a loop here for performance reasons
+			// PERF: Avoid LINQ.
 			foreach (var rfa in removeFrozenActors)
 				if (rfa.RemoveActor(actor, owner))
 					return true;

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -50,6 +50,7 @@ namespace OpenRA.Traits
 	{
 		public static bool HasStance(this Stance s, Stance stance)
 		{
+			// PERF: Enum.HasFlag is slower and requires allocations.
 			return (s & stance) == stance;
 		}
 	}
@@ -92,7 +93,11 @@ namespace OpenRA.Traits
 
 	public static class TargetModifiersExts
 	{
-		public static bool HasModifier(this TargetModifiers self, TargetModifiers m) { return (self & m) == m; }
+		public static bool HasModifier(this TargetModifiers self, TargetModifiers m)
+		{
+			// PERF: Enum.HasFlag is slower and requires allocations.
+			return (self & m) == m;
+		}
 	}
 
 	public interface IOrderTargeter

OpenRA.Game/Traits/Util.cs

@@ -74,10 +74,15 @@ namespace OpenRA.Traits
 
 		public static Activity RunActivity(Actor self, Activity act)
 		{
+			// PERF: If there are no activities we can bail straight away and save ourselves a call to
+			// Stopwatch.GetTimestamp.
 			if (act == null)
 				return act;
 
-			// Note - manual iteration here for performance due to high call volume.
+			// PERF: This is a hot path and must run with minimal added overhead.
+			// Calling Stopwatch.GetTimestamp is a bit expensive, so we enumerate manually to allow us to call it only
+			// once per iteration in the normal case.
+			// See also: DoTimed
 			var longTickThresholdInStopwatchTicks = PerfTimer.LongTickThresholdInStopwatchTicks;
 			var start = Stopwatch.GetTimestamp();
 			while (act != null)

OpenRA.Game/Traits/World/ActorMap.cs

@@ -183,7 +183,7 @@ namespace OpenRA.Traits
 				for (var col = 0; col < cols; col++)
 					bins[row * cols + col] = new Bin();
 
-			// Cache this delegate so it does not have to be allocated repeatedly.
+			// PERF: Cache this delegate so it does not have to be allocated repeatedly.
 			actorShouldBeRemoved = removeActorPosition.Contains;
 		}
 
@@ -219,6 +219,7 @@ namespace OpenRA.Traits
 
 		public IEnumerable<Actor> GetActorsAt(CPos a)
 		{
+			// PERF: Custom enumerator for efficiency - using `yield` is slower.
 			var uv = a.ToMPos(map);
 			if (!influence.Contains(uv))
 				return Enumerable.Empty<Actor>();
@@ -534,6 +535,7 @@ namespace OpenRA.Traits
 
 		public IEnumerable<Actor> ActorsInBox(WPos a, WPos b)
 		{
+			// PERF: Inline BinsInBox here to avoid allocations as this method is called often.
 			var left = Math.Min(a.X, b.X);
 			var top = Math.Min(a.Y, b.Y);
 			var right = Math.Max(a.X, b.X);