ConstructorExpression: No many clones of empty collection

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Linq/Expressions/ConstructorExpression.cs

@@ -14,6 +14,7 @@
 using Xtensive.Orm.Linq.Expressions;
 using Xtensive.Orm.Linq.Expressions.Visitors;
 using System.Linq;
+using System.Net.Http.Headers;
 
 namespace Xtensive.Orm.Linq
 {
@@ -33,24 +34,30 @@ public Expression BindParameter(ParameterExpression parameter, Dictionary<Expres
     {
       Func<Expression, Expression> genericBinder =
         e => GenericExpressionVisitor<IMappedExpression>.Process(e, mapped => mapped.BindParameter(parameter, processedExpressions));
+
       return new ConstructorExpression(
         Type,
         Bindings.ToDictionary(kvp => kvp.Key, kvp => genericBinder(kvp.Value), Bindings.Count),
         NativeBindings.ToDictionary(kvp=>kvp.Key, kvp => genericBinder(kvp.Value), NativeBindings.Count),
         Constructor,
-        ConstructorArguments.Select(genericBinder).ToArray());
+        ReferenceEquals(ConstructorArguments, Array.Empty<Expression>())
+          ? ConstructorArguments
+          : ConstructorArguments.Select(genericBinder).ToArray());
     }
 
     public Expression RemoveOuterParameter(Dictionary<Expression, Expression> processedExpressions)
     {
       Func<Expression, Expression> genericRemover =
         e => GenericExpressionVisitor<IMappedExpression>.Process(e, mapped => mapped.RemoveOuterParameter(processedExpressions));
+
       var result = new ConstructorExpression(
         Type,
         Bindings.ToDictionary(kvp => kvp.Key, kvp => genericRemover(kvp.Value)),
         NativeBindings = NativeBindings.ToDictionary(kvp => kvp.Key, kvp => genericRemover(kvp.Value)),
         Constructor,
-        ConstructorArguments.Select(genericRemover).ToArray());
+        ReferenceEquals(ConstructorArguments, Array.Empty<Expression>())
+          ? ConstructorArguments
+          : ConstructorArguments.Select(genericRemover).ToArray());
       return result;
     }
 
@@ -62,8 +69,11 @@ public Expression Remap(int offset, Dictionary<Expression, Expression> processed
           return mapped.Remap(offset, new Dictionary<Expression, Expression>());
         return (Expression) mapped;
       };
+
       var newBindings = Bindings.ToDictionary(kvp => kvp.Key, kvp => GenericExpressionVisitor<IMappedExpression>.Process(kvp.Value, remapper));
-      var newConstructorArguments = ConstructorArguments.Select(arg =>  GenericExpressionVisitor<IMappedExpression>.Process(arg, remapper));
+      var newConstructorArguments = ReferenceEquals(ConstructorArguments, Array.Empty<Expression>())
+        ? ConstructorArguments
+        : ConstructorArguments.Select(arg =>  GenericExpressionVisitor<IMappedExpression>.Process(arg, remapper));
       var newNativeBindings = NativeBindings.ToDictionary(kvp => kvp.Key, kvp => GenericExpressionVisitor<IMappedExpression>.Process(kvp.Value, remapper));
       var result = new ConstructorExpression(
         Type,
@@ -82,18 +92,27 @@ public Expression Remap(IReadOnlyList<int> map, Dictionary<Expression, Expressio
           return mapped.Remap(map, new Dictionary<Expression, Expression>());
         return (Expression) mapped;
       };
+
       var newBindings = Bindings.ToDictionary(kvp => kvp.Key, kvp => GenericExpressionVisitor<IMappedExpression>.Process(kvp.Value, remapper));
-      var newConstructorArguments = ConstructorArguments.Select(arg =>  GenericExpressionVisitor<IMappedExpression>.Process(arg, remapper));
+      var newConstructorArguments = ReferenceEquals(ConstructorArguments, Array.Empty<Expression>())
+        ? ConstructorArguments
+        : ConstructorArguments.Select(arg =>  GenericExpressionVisitor<IMappedExpression>.Process(arg, remapper));
       var newNativeBindings = NativeBindings.ToDictionary(kvp => kvp.Key, kvp => GenericExpressionVisitor<IMappedExpression>.Process(kvp.Value, remapper));
       return new ConstructorExpression(Type, newBindings, newNativeBindings, Constructor, newConstructorArguments);
     }
 
-    public ConstructorExpression(Type type, Dictionary<MemberInfo, Expression> bindings, Dictionary<MemberInfo, Expression> nativeBindings, ConstructorInfo constructor, IEnumerable<Expression> constructorArguments)
+    public ConstructorExpression(Type type,
+      Dictionary<MemberInfo, Expression> bindings,
+      Dictionary<MemberInfo, Expression> nativeBindings,
+      ConstructorInfo constructor,
+      IEnumerable<Expression> constructorArguments)
       : base(ExtendedExpressionType.Constructor, type, null, false)
     {
       Bindings = bindings ?? new Dictionary<MemberInfo, Expression>();
       NativeBindings = nativeBindings;
-      ConstructorArguments = constructorArguments ?? Enumerable.Empty<Expression>();
+      // consistently use keep empty array instead of any other empty collection,
+      // there are checks that help to not instanciate collections
+      ConstructorArguments = constructorArguments ?? Array.Empty<Expression>();
       Constructor = constructor;
     }
   }

Orm/Xtensive.Orm/Orm/Linq/Expressions/Visitors/ExtendedExpressionReplacer.cs

@@ -6,6 +6,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
 using Xtensive.Orm.Rse.Providers;
@@ -115,7 +116,7 @@ protected override ColumnExpression VisitColumnExpression(ColumnExpression expre
 
     protected override ConstructorExpression VisitConstructorExpression(ConstructorExpression expression)
     {
-      var arguments = new List<Expression>();
+      IList<Expression> arguments = new List<Expression>();
       var bindings = new Dictionary<MemberInfo, Expression>(expression.Bindings.Count);
       var nativeBindings = new Dictionary<MemberInfo, Expression>(expression.NativeBindings.Count);
       bool recreate = false;
@@ -144,7 +145,7 @@ protected override ConstructorExpression VisitConstructorExpression(ConstructorE
         bindings,
         nativeBindings,
         expression.Constructor,
-        arguments);
+        arguments.Count > 0 ? arguments : Array.Empty<Expression>());
     }
 
     protected override MarkerExpression VisitMarker(MarkerExpression expression)

Orm/Xtensive.Orm/Orm/Linq/Expressions/Visitors/OwnerRemover.cs

@@ -4,6 +4,8 @@
 // Created by: Alexis Kochetov
 // Created:    2009.05.26
 
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Linq.Expressions;
 using Xtensive.Core;
@@ -45,8 +47,23 @@ protected override KeyExpression VisitKeyExpression(KeyExpression expression)
 
     protected override ConstructorExpression VisitConstructorExpression(ConstructorExpression expression)
     {
-      var oldConstructorArguments = expression.ConstructorArguments.ToList();
-      var newConstructorArguments = VisitExpressionList(oldConstructorArguments);
+      IReadOnlyList<Expression> oldConstructorArguments;
+      IReadOnlyList<Expression> newConstructorArguments;
+
+      if (ReferenceEquals(expression.ConstructorArguments, Array.Empty<Expression>())) {
+        oldConstructorArguments = newConstructorArguments = Array.Empty<Expression>();
+      }
+      else if (expression.ConstructorArguments is IReadOnlyList<Expression> argsAsList) {
+        oldConstructorArguments = argsAsList;
+        newConstructorArguments = VisitExpressionList(argsAsList); // creates a copy internally
+      }
+      else {
+        oldConstructorArguments = expression.ConstructorArguments.ToList();
+        if (oldConstructorArguments.Count == 0)
+          oldConstructorArguments = newConstructorArguments = Array.Empty<Expression>();
+        else
+          newConstructorArguments = VisitExpressionList(oldConstructorArguments);
+      }
 
       var oldBindings = expression.Bindings.SelectToList(b => b.Value);
       var newBindings = VisitExpressionList(oldBindings);

Orm/Xtensive.Orm/Orm/Linq/Translator.Expressions.cs

@@ -690,9 +690,11 @@ protected override Expression VisitNew(NewExpression newExpression)
       // ReSharper restore ConditionIsAlwaysTrueOrFalse
       // ReSharper restore HeuristicUnreachableCode
 
-      var arguments = VisitNewExpressionArguments(newExpression);
+      IList<Expression> arguments = VisitNewExpressionArguments(newExpression);
+      if (arguments.Count == 0)
+        arguments = Array.Empty<Expression>();
       if (newExpression.IsAnonymousConstructor()) {
-        return newExpression.Members==null
+        return newExpression.Members == null
           ? Expression.New(newExpression.Constructor, arguments)
           : Expression.New(newExpression.Constructor, arguments, newExpression.Members);
       }