Fixing Delegate's hash code's distribution (#11019)

Delegate's GetHashCode just returns the hash code of the delegate type. For a scenario where delegates are used as keys in a dictionary, this leads to obvious performance problems. We should look at coming up with a better GetHashCode that properly factors in the target object and method, in all of the various forms a delegate can take.

Author: mountgellert

src/mscorlib/src/System/Delegate.cs

@@ -179,7 +179,10 @@ public override int GetHashCode()
             else
                 return unchecked((int)((long)this._methodPtrAux));
             */
-            return GetType().GetHashCode();
+            if (_methodPtrAux.IsNull())
+                return ( _target != null ? RuntimeHelpers.GetHashCode(_target) * 33 : 0) + GetType().GetHashCode();
+            else
+                return GetType().GetHashCode();
         }
 
         public static Delegate Combine(Delegate a, Delegate b)

tests/src/CoreMangLib/cti/system/delegate/delegategethashcode1.cs

@@ -218,15 +218,15 @@ public bool PosTest7()
         {
             bool retVal = true;
 
-            TestLibrary.TestFramework.BeginScenario("PosTest7:  Use the different instance's same instance method to create two delegate which delegate object is the same,their hashcode is equal");
+            TestLibrary.TestFramework.BeginScenario("PosTest7:  Use the different instance's same instance method to create two delegate which delegate object is the same, their hashcode is different");
 
             try
             {
                 DelegateGetHashCode delctor = new DelegateGetHashCode();
                 booldelegate workDelegate = new booldelegate(new TestClass(1).StartWork_Bool);
                 booldelegate workDelegate1 = new booldelegate(new TestClass1(2).StartWork_Bool );
 
-                if (workDelegate.GetHashCode()!=workDelegate1.GetHashCode())
+                if (workDelegate.GetHashCode()==workDelegate1.GetHashCode())
                 {
                     TestLibrary.TestFramework.LogError("013", "HashCode is not excepted ");
                     retVal = false;