Optimize allocations for creating ActionConstraints

src/Microsoft.AspNet.Mvc.Core/ActionConstraints/DefaultActionConstraintProvider.cs

@@ -29,9 +29,9 @@ namespace Microsoft.AspNet.Mvc.ActionConstraints
                 throw new ArgumentNullException(nameof(context));
             }
 
-            foreach (var item in context.Results)
+            for (var i = 0; i < context.Results.Count; i++)
             {
-                ProvideConstraint(item, context.HttpContext.RequestServices);
+                ProvideConstraint(context.Results[i], context.HttpContext.RequestServices);
             }
         }
 

src/Microsoft.AspNet.Mvc.Core/ActionConstraints/HttpMethodConstraint.cs

@@ -13,7 +13,7 @@ namespace Microsoft.AspNet.Mvc.ActionConstraints
     {
         public static readonly int HttpMethodConstraintOrder = 100;
 
-        private readonly IReadOnlyList<string> _methods;
+        private readonly IReadOnlyList<string> _httpMethods;
 
         private readonly string OriginHeader = "Origin";
         private readonly string AccessControlRequestMethod = "Access-Control-Request-Method";
@@ -39,14 +39,14 @@ namespace Microsoft.AspNet.Mvc.ActionConstraints
                 methods.Add(method);
             }
 
-            _methods = new ReadOnlyCollection<string>(methods);
+            _httpMethods = new ReadOnlyCollection<string>(methods);
         }
 
         public IEnumerable<string> HttpMethods
         {
             get
             {
-                return _methods;
+                return _httpMethods;
             }
         }
 
@@ -62,7 +62,7 @@ namespace Microsoft.AspNet.Mvc.ActionConstraints
                 throw new ArgumentNullException(nameof(context));
             }
 
-            if (_methods.Count == 0)
+            if (_httpMethods.Count == 0)
             {
                 return true;
             }
@@ -83,7 +83,16 @@ namespace Microsoft.AspNet.Mvc.ActionConstraints
                 }
             }
 
-            return (HttpMethods.Any(m => m.Equals(method, StringComparison.Ordinal)));
+            for (var i = 0; i < _httpMethods.Count; i++)
+            {
+                var supportedMethod = _httpMethods[i];
+                if (string.Equals(supportedMethod, method, StringComparison.Ordinal))
+                {
+                    return true;
+                }
+            }
+
+            return false;
         }
     }
 }

src/Microsoft.AspNet.Mvc.Core/Infrastructure/DefaultActionSelector.cs

@@ -260,12 +260,16 @@ namespace Microsoft.AspNet.Mvc.Infrastructure
                 return null;
             }
 
-            var items = action.ActionConstraints.Select(c => new ActionConstraintItem(c)).ToList();
-            var context = new ActionConstraintProviderContext(httpContext, action, items);
-
-            foreach (var provider in _actionConstraintProviders)
+            var items = new List<ActionConstraintItem>(action.ActionConstraints.Count);
+            for (var i = 0; i < action.ActionConstraints.Count; i++)
             {
-                provider.OnProvidersExecuting(context);
+                items.Add(new ActionConstraintItem(action.ActionConstraints[i]));
+            }
+
+            var context = new ActionConstraintProviderContext(httpContext, action, items);
+            for (var i = 0; i < _actionConstraintProviders.Length; i++)
+            {
+                _actionConstraintProviders[i].OnProvidersExecuting(context);
             }
 
             for (var i = _actionConstraintProviders.Length - 1; i >= 0; i--)
@@ -273,11 +277,31 @@ namespace Microsoft.AspNet.Mvc.Infrastructure
                 _actionConstraintProviders[i].OnProvidersExecuted(context);
             }
 
-            return
-                context.Results
-                .Where(item => item.Constraint != null)
-                .Select(item => item.Constraint)
-                .ToList();
+            var count = 0;
+            for (var i = 0; i < context.Results.Count; i++)
+            {
+                if (context.Results[i].Constraint != null)
+                {
+                    count++;
+                }
+            }
+
+            if (count == 0)
+            {
+                return null;
+            }
+
+            var results = new IActionConstraint[count];
+            for (int i = 0, j = 0; i < context.Results.Count; i++)
+            {
+                var constraint = context.Results[i].Constraint;
+                if (constraint != null)
+                {
+                    results[j++] = constraint;
+                }
+            }
+
+            return results;
         }
     }
 }