Mitigate some of #495 via MRO member selection and analysis set optimization

src/Analysis/Engine/Impl/AnalysisHashSet.cs

@@ -275,7 +275,19 @@ public bool SetEquals(IAnalysisSet other) {
                 return true;
             }
 
+            // Only access Count once to prevent wasted time in bucket locks.
+            var lCount = Count;
+            var rCount = other.Count;
+
+            if (lCount == 0 && rCount == 0) {
+                return true;
+            }
+
             if (Comparer == other.Comparer) {
+                if (lCount != rCount) {
+                    return false;
+                }
+
                 // Quick check for any unmatched hashcodes.
                 // This can conclusively prove the sets are not equal, but cannot
                 // prove equality.
@@ -290,17 +302,16 @@ public bool SetEquals(IAnalysisSet other) {
                 }
             }
 
-            var otherHc = new HashSet<AnalysisValue>(other, _comparer);
-            foreach (var key in this) {
-                if (!otherHc.Remove(key)) {
-                    return false;
-                }
-            }
-            if (otherHc.Any()) {
+            if (lCount == 0 || rCount == 0) {
                 return false;
             }
 
-            return true;
+            if (lCount == 1 && rCount == 1) {
+                return _comparer.Equals(this.First(), other.First());
+            }
+
+            var hs = new HashSet<AnalysisValue>(other, _comparer);
+            return hs.SetEquals(this);
         }
 
         /// <summary>

src/Analysis/Engine/Impl/AnalysisSet.cs

@@ -534,6 +534,8 @@ public static bool ContainsAny(this IAnalysisSet set, IAnalysisSet values) {
     sealed class ObjectComparer : IEqualityComparer<AnalysisValue>, IEqualityComparer<IAnalysisSet> {
         public static readonly ObjectComparer Instance = new ObjectComparer();
 
+        private ObjectComparer() { }
+
         public bool Equals(AnalysisValue x, AnalysisValue y) {
 #if FULL_VALIDATION
             if (x != null && y != null) {
@@ -574,7 +576,7 @@ sealed class UnionComparer : IEqualityComparer<AnalysisValue>, IEqualityComparer
 
         public readonly int Strength;
 
-        public UnionComparer(int strength = 0) {
+        private UnionComparer(int strength = 0) {
             Strength = strength;
         }
 

src/Analysis/Engine/Impl/Intellisense/AnalysisQueue.cs

@@ -206,7 +206,7 @@ public async Task Handler(CancellationToken cancellationToken) {
         }
 
         private sealed class QueueItemComparer : IEqualityComparer<QueueItem> {
-            public static IEqualityComparer<QueueItem> Instance { get; } = new QueueItemComparer();
+            public static readonly IEqualityComparer<QueueItem> Instance = new QueueItemComparer();
 
             private QueueItemComparer() { }
             public bool Equals(QueueItem x, QueueItem y) => Equals(x.Key, y.Key);

src/Analysis/Engine/Impl/LocationInfo.cs

@@ -83,9 +83,13 @@ public bool Equals(ILocationInfo other) {
         /// Provides an IEqualityComparer that compares line, column and project entries.  By
         /// default locations are equaitable based upon only line/project entry.
         /// </summary>
-        public static IEqualityComparer<ILocationInfo> FullComparer { get; } = new FullLocationComparer();
+        public static IEqualityComparer<ILocationInfo> FullComparer => FullLocationComparer.Instance;
 
         sealed class FullLocationComparer : IEqualityComparer<ILocationInfo>, IEqualityComparer<LocationInfo> {
+            public static readonly FullLocationComparer Instance = new FullLocationComparer();
+
+            private FullLocationComparer() { }
+
             public bool Equals(LocationInfo x, LocationInfo y) => Equals(x, y);
             public bool Equals(ILocationInfo x, ILocationInfo y) {
                 return x.StartLine == y.StartLine &&

src/Analysis/Engine/Impl/OverloadResult.cs

@@ -425,8 +425,8 @@ internal ParameterResult GetParameterResultFromParameterInfo(IParameterInfo para
     }
 
     class OverloadResultComparer : EqualityComparer<OverloadResult> {
-        public static IEqualityComparer<OverloadResult> Instance = new OverloadResultComparer(false);
-        public static IEqualityComparer<OverloadResult> WeakInstance = new OverloadResultComparer(true);
+        public static readonly IEqualityComparer<OverloadResult> Instance = new OverloadResultComparer(false);
+        public static readonly IEqualityComparer<OverloadResult> WeakInstance = new OverloadResultComparer(true);
 
         private readonly bool _weak;
 

src/Analysis/Engine/Impl/PythonAnalyzer.cs

@@ -921,7 +921,9 @@ private AggregateProjectEntry GetAggregateWorker(IProjectEntry[] all) {
         }
 
         class AggregateComparer : IEqualityComparer<IProjectEntry[]> {
-            public static AggregateComparer Instance = new AggregateComparer();
+            public static readonly AggregateComparer Instance = new AggregateComparer();
+
+            private AggregateComparer() { }
 
             public bool Equals(IProjectEntry[] x, IProjectEntry[] y) {
                 if (x.Length != y.Length) {

src/Analysis/Engine/Impl/Values/ClassInfo.cs

@@ -831,6 +831,10 @@ public static IAnalysisSet GetMemberFromMroNoReferences(IEnumerable<IAnalysisSet
                         result = result.Union(ns.GetMember(node, unit, name));
                     }
                 }
+
+                if (result != null && result.Count > 0) {
+                    break;
+                }
             }
             return result;
         }