Pool the simplifiers we create while simplifying code.

src/Workspaces/CSharp/Portable/CSharpWorkspace.csproj

@@ -209,22 +209,22 @@
     <Compile Include="Rename\CSharpRenameRewriterLanguageService.cs" />
     <Compile Include="Rename\LabelConflictVisitor.cs" />
     <Compile Include="Rename\LocalConflictVisitor.cs" />
-    <Compile Include="Simplification\AbstractCSharpReducer.AbstractExpressionRewriter.cs" />
-    <Compile Include="Simplification\AbstractCSharpReducer.cs" />
-    <Compile Include="Simplification\CSharpCastReducer.cs" />
-    <Compile Include="Simplification\CSharpInferredMemberNameReducer.cs" />
-    <Compile Include="Simplification\CSharpInferredMemberNameReducer.Rewriter.cs" />
-    <Compile Include="Simplification\CSharpCastReducer.Rewriter.cs" />
-    <Compile Include="Simplification\CSharpEscapingReducer.cs" />
-    <Compile Include="Simplification\CSharpEscapingReducer.Rewriter.cs" />
-    <Compile Include="Simplification\CSharpExtensionMethodReducer.cs" />
-    <Compile Include="Simplification\CSharpExtensionMethodReducer.Rewriter.cs" />
-    <Compile Include="Simplification\CSharpMiscellaneousReducer.cs" />
-    <Compile Include="Simplification\CSharpMiscellaneousReducer.Rewriter.cs" />
-    <Compile Include="Simplification\CSharpNameReducer.cs" />
-    <Compile Include="Simplification\CSharpNameReducer.Rewriter.cs" />
-    <Compile Include="Simplification\CSharpParenthesesReducer.cs" />
-    <Compile Include="Simplification\CSharpParenthesesReducer.Rewriter.cs" />
+    <Compile Include="Simplification\Reducers\AbstractCSharpReducer.AbstractReductionRewriter.cs" />
+    <Compile Include="Simplification\Reducers\AbstractCSharpReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpCastReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpInferredMemberNameReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpInferredMemberNameReducer.Rewriter.cs" />
+    <Compile Include="Simplification\Reducers\CSharpCastReducer.Rewriter.cs" />
+    <Compile Include="Simplification\Reducers\CSharpEscapingReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpEscapingReducer.Rewriter.cs" />
+    <Compile Include="Simplification\Reducers\CSharpExtensionMethodReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpExtensionMethodReducer.Rewriter.cs" />
+    <Compile Include="Simplification\Reducers\CSharpMiscellaneousReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpMiscellaneousReducer.Rewriter.cs" />
+    <Compile Include="Simplification\Reducers\CSharpNameReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpNameReducer.Rewriter.cs" />
+    <Compile Include="Simplification\Reducers\CSharpParenthesesReducer.cs" />
+    <Compile Include="Simplification\Reducers\CSharpParenthesesReducer.Rewriter.cs" />
     <Compile Include="Simplification\CSharpSimplificationService.cs" />
     <Compile Include="Simplification\CSharpSimplificationService.Expander.cs" />
     <Compile Include="Simplification\CSharpSimplificationService.NodesAndTokensToReduceComputer.cs" />

src/Workspaces/CSharp/Portable/CodeGeneration/CSharpSyntaxGenerator.cs

@@ -3524,9 +3524,7 @@ public override SyntaxNode IfStatement(SyntaxNode condition, IEnumerable<SyntaxN
         }
 
         private BlockSyntax CreateBlock(IEnumerable<SyntaxNode> statements)
-        {
-            return SyntaxFactory.Block(AsStatementList(statements));
-        }
+            => SyntaxFactory.Block(AsStatementList(statements)).WithAdditionalAnnotations(Simplifier.Annotation);
 
         private SyntaxList<StatementSyntax> AsStatementList(IEnumerable<SyntaxNode> nodes)
         {

src/Workspaces/CSharp/Portable/Simplification/AbstractCSharpReducer.AbstractExpressionRewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/AbstractCSharpReducer.AbstractReductionRewriter.cs

@@ -5,34 +5,51 @@
 using System.Diagnostics;
 using System.Linq;
 using System.Threading;
-using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Simplification;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal abstract partial class AbstractCSharpReducer
     {
-        protected abstract class AbstractExpressionRewriter : CSharpSyntaxRewriter, IExpressionRewriter
+        protected abstract class AbstractReductionRewriter : CSharpSyntaxRewriter, IReductionRewriter
         {
-            private readonly OptionSet _optionSet;
-            private readonly CancellationToken _cancellationToken;
-            private readonly HashSet<SyntaxNode> _processedParentNodes;
+            private readonly ObjectPool<IReductionRewriter> _pool;
+
+            private OptionSet _optionSet;
+            private CancellationToken _cancellationToken;
             private SemanticModel _semanticModel;
 
-            protected AbstractExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+            public bool HasMoreWork { get; private set; }
+
+            // can be used to simplify whole subtrees while just annotating one syntax node.
+            // This is e.g. useful in the name simplification, where a whole qualified name is annotated
+            protected bool alwaysSimplify;
+
+            private HashSet<SyntaxNode> _processedParentNodes = new HashSet<SyntaxNode>();
+
+            protected AbstractReductionRewriter(ObjectPool<IReductionRewriter> pool)
+                => _pool = pool;
+
+            public void Initialize(OptionSet optionSet, CancellationToken cancellationToken)
             {
                 _optionSet = optionSet;
                 _cancellationToken = cancellationToken;
-                _processedParentNodes = new HashSet<SyntaxNode>();
             }
 
-            public bool HasMoreWork { get; private set; }
+            public void Dispose()
+            {
+                _optionSet = null;
+                _cancellationToken = CancellationToken.None;
+                _processedParentNodes.Clear();
+                _semanticModel = null;
+                HasMoreWork = false;
+                alwaysSimplify = false;
 
-            // can be used to simplify whole subtrees while just annotating one syntax node.
-            // This is e.g. useful in the name simplification, where a whole qualified name is annotated
-            protected bool alwaysSimplify;
+                _pool.Free(this);
+            }
 
             private static SyntaxNode GetParentNode(SyntaxNode node)
             {
@@ -173,4 +190,4 @@ public SyntaxNodeOrToken VisitNodeOrToken(SyntaxNodeOrToken nodeOrToken, Semanti
             }
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/AbstractCSharpReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/AbstractCSharpReducer.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using Microsoft.CodeAnalysis.Simplification;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal abstract partial class AbstractCSharpReducer : AbstractReducer
     {
+        protected AbstractCSharpReducer(ObjectPool<IReductionRewriter> pool) : base(pool)
+        {
+        }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpCastReducer.Rewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpCastReducer.Rewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System.Linq;
-using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Simplification;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpCastReducer
     {
-        private class Rewriter : AbstractExpressionRewriter
+        private class Rewriter : AbstractReductionRewriter
         {
-            public Rewriter(OptionSet optionSet, CancellationToken cancellationToken)
-                : base(optionSet, cancellationToken)
+            public Rewriter(ObjectPool<IReductionRewriter> pool)
+                : base(pool)
             {
             }
 
@@ -69,4 +68,4 @@ public override SyntaxNode VisitBinaryExpression(BinaryExpressionSyntax node)
             }
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpCastReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpCastReducer.cs

@@ -8,14 +8,17 @@
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Simplification;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpCastReducer : AbstractCSharpReducer
     {
-        public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+        private static readonly ObjectPool<IReductionRewriter> s_pool = new ObjectPool<IReductionRewriter>(
+            () => new Rewriter(s_pool));
+
+        public CSharpCastReducer() : base(s_pool)
         {
-            return new Rewriter(optionSet, cancellationToken);
         }
 
         private static readonly Func<CastExpressionSyntax, SemanticModel, OptionSet, CancellationToken, ExpressionSyntax> s_simplifyCast = SimplifyCast;

src/Workspaces/CSharp/Portable/Simplification/CSharpEscapingReducer.Rewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpEscapingReducer.Rewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Threading;
-using Microsoft.CodeAnalysis.Options;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpEscapingReducer
     {
-        private class Rewriter : AbstractExpressionRewriter
+        private class Rewriter : AbstractReductionRewriter
         {
-            public Rewriter(CSharpEscapingReducer escapingSimplifierService, OptionSet optionSet, CancellationToken cancellationToken)
-                : base(optionSet, cancellationToken)
+            public Rewriter(ObjectPool<IReductionRewriter> pool)
+                : base(pool)
             {
-                _escapingSimplifierService = escapingSimplifierService;
             }
 
-            private readonly CSharpEscapingReducer _escapingSimplifierService;
-
             public override SyntaxToken VisitToken(SyntaxToken token)
             {
                 var newToken = base.VisitToken(token);

src/Workspaces/CSharp/Portable/Simplification/CSharpEscapingReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpEscapingReducer.cs

@@ -8,14 +8,17 @@
 using Microsoft.CodeAnalysis.CSharp.Utilities;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpEscapingReducer : AbstractCSharpReducer
     {
-        public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+        private static readonly ObjectPool<IReductionRewriter> s_pool = new ObjectPool<IReductionRewriter>(
+            () => new Rewriter(s_pool));
+
+        public CSharpEscapingReducer() : base(s_pool)
         {
-            return new Rewriter(this, optionSet, cancellationToken);
         }
 
         private static Func<SyntaxToken, SemanticModel, OptionSet, CancellationToken, SyntaxToken> s_simplifyIdentifierToken = SimplifyIdentifierToken;
@@ -132,4 +135,4 @@ private static SyntaxToken CreateNewIdentifierTokenFromToken(SyntaxToken origina
                 : originalToken.CopyAnnotationsTo(SyntaxFactory.Identifier(originalToken.LeadingTrivia, SyntaxKind.IdentifierToken, unescapedText, originalToken.ValueText, originalToken.TrailingTrivia));
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpExtensionMethodReducer.Rewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpExtensionMethodReducer.Rewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Options;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpExtensionMethodReducer
     {
-        private class Rewriter : AbstractExpressionRewriter
+        private class Rewriter : AbstractReductionRewriter
         {
-            public Rewriter(OptionSet optionSet, CancellationToken cancellationToken)
-                : base(optionSet, cancellationToken)
+            public Rewriter(ObjectPool<IReductionRewriter> pool)
+                : base(pool)
             {
             }
 

src/Workspaces/CSharp/Portable/Simplification/CSharpExtensionMethodReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpExtensionMethodReducer.cs

@@ -8,14 +8,17 @@
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpExtensionMethodReducer : AbstractCSharpReducer
     {
-        public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+        private static readonly ObjectPool<IReductionRewriter> s_pool = new ObjectPool<IReductionRewriter>(
+            () => new Rewriter(s_pool));
+
+        public CSharpExtensionMethodReducer() : base(s_pool)
         {
-            return new Rewriter(optionSet, cancellationToken);
         }
 
         private static readonly Func<InvocationExpressionSyntax, SemanticModel, OptionSet, CancellationToken, SyntaxNode> s_simplifyExtensionMethod = SimplifyExtensionMethod;
@@ -67,19 +70,19 @@ private static InvocationExpressionSyntax TryReduceExtensionMethod(InvocationExp
                         {
                             newMemberAccess = SyntaxFactory.MemberAccessExpression(
                                 SyntaxKind.SimpleMemberAccessExpression, expression,
-                                ((MemberAccessExpressionSyntax)invocationExpressionNodeExpression).OperatorToken, 
+                                ((MemberAccessExpressionSyntax)invocationExpressionNodeExpression).OperatorToken,
                                 ((MemberAccessExpressionSyntax)invocationExpressionNodeExpression).Name);
                         }
                         else if (node.Expression.Kind() == SyntaxKind.IdentifierName)
                         {
                             newMemberAccess = SyntaxFactory.MemberAccessExpression(
-                                SyntaxKind.SimpleMemberAccessExpression, expression, 
+                                SyntaxKind.SimpleMemberAccessExpression, expression,
                                 (IdentifierNameSyntax)invocationExpressionNodeExpression.WithoutLeadingTrivia());
                         }
                         else if (node.Expression.Kind() == SyntaxKind.GenericName)
                         {
                             newMemberAccess = SyntaxFactory.MemberAccessExpression(
-                                SyntaxKind.SimpleMemberAccessExpression, expression, 
+                                SyntaxKind.SimpleMemberAccessExpression, expression,
                                 (GenericNameSyntax)invocationExpressionNodeExpression.WithoutLeadingTrivia());
                         }
                         else
@@ -122,4 +125,4 @@ private static InvocationExpressionSyntax TryReduceExtensionMethod(InvocationExp
             return rewrittenNode;
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpInferredMemberNameReducer.Rewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpInferredMemberNameReducer.Rewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System;
-using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Options;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpInferredMemberNameReducer
     {
-        private class Rewriter : AbstractExpressionRewriter
+        private class Rewriter : AbstractReductionRewriter
         {
-            public Rewriter(OptionSet optionSet, CancellationToken cancellationToken)
-                : base(optionSet, cancellationToken)
+            public Rewriter(ObjectPool<IReductionRewriter> pool)
+                : base(pool)
             {
             }
 
@@ -42,4 +40,4 @@ public override SyntaxNode VisitAnonymousObjectMemberDeclarator(AnonymousObjectM
             }
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpInferredMemberNameReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpInferredMemberNameReducer.cs

@@ -5,6 +5,7 @@
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Options;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
@@ -15,9 +16,11 @@ namespace Microsoft.CodeAnalysis.CSharp.Simplification
     /// </summary>
     internal partial class CSharpInferredMemberNameReducer : AbstractCSharpReducer
     {
-        public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+        private static readonly ObjectPool<IReductionRewriter> s_pool = new ObjectPool<IReductionRewriter>(
+            () => new Rewriter(s_pool));
+
+        public CSharpInferredMemberNameReducer() : base(s_pool)
         {
-            return new Rewriter(optionSet, cancellationToken);
         }
 
         private static readonly Func<ArgumentSyntax, SemanticModel, OptionSet, CancellationToken, ArgumentSyntax> s_simplifyTupleName = SimplifyTupleName;
@@ -59,4 +62,4 @@ private static SyntaxNode SimplifyAnonymousTypeMemberName(AnonymousObjectMemberD
             return node.WithNameEquals(null).WithTriviaFrom(node);
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpMiscellaneousReducer.Rewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpMiscellaneousReducer.Rewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Options;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpMiscellaneousReducer
     {
-        private class Rewriter : AbstractExpressionRewriter
+        private class Rewriter : AbstractReductionRewriter
         {
-            public Rewriter(OptionSet optionSet, CancellationToken cancellationToken)
-                : base(optionSet, cancellationToken)
+            public Rewriter(ObjectPool<IReductionRewriter> pool)
+                : base(pool)
             {
             }
 

src/Workspaces/CSharp/Portable/Simplification/CSharpMiscellaneousReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpMiscellaneousReducer.cs

@@ -8,14 +8,17 @@
 using Microsoft.CodeAnalysis.CSharp.Utilities;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Simplification;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpMiscellaneousReducer : AbstractCSharpReducer
     {
-        public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+        private static readonly ObjectPool<IReductionRewriter> s_pool = new ObjectPool<IReductionRewriter>(
+            () => new Rewriter(s_pool));
+
+        public CSharpMiscellaneousReducer() : base(s_pool)
         {
-            return new Rewriter(optionSet, cancellationToken);
         }
 
         private static bool CanRemoveTypeFromParameter(
@@ -101,4 +104,4 @@ public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet
             return node;
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpNameReducer.Rewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpNameReducer.Rewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Threading;
-using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Formatting;
-using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Simplification;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpNameReducer
     {
-        private class Rewriter : AbstractExpressionRewriter
+        private class Rewriter : AbstractReductionRewriter
         {
-            public Rewriter(OptionSet optionSet, CancellationToken cancellationToken)
-                : base(optionSet, cancellationToken)
+            public Rewriter(ObjectPool<IReductionRewriter> pool)
+                : base(pool)
             {
             }
 
@@ -201,4 +199,4 @@ public override SyntaxNode VisitBinaryExpression(BinaryExpressionSyntax node)
             }
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpNameReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpNameReducer.cs

@@ -8,14 +8,17 @@
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Simplification;
 using Microsoft.CodeAnalysis.Text;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpNameReducer : AbstractCSharpReducer
     {
-        public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+        private static readonly ObjectPool<IReductionRewriter> s_pool = new ObjectPool<IReductionRewriter>(
+            () => new Rewriter(s_pool));
+
+        public CSharpNameReducer() : base(s_pool)
         {
-            return new Rewriter(optionSet, cancellationToken);
         }
 
         private static readonly Func<SyntaxNode, SemanticModel, OptionSet, CancellationToken, SyntaxNode> s_simplifyName = SimplifyName;
@@ -54,4 +57,4 @@ public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet
             return node.WithoutAnnotations(Simplifier.Annotation);
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/CSharp/Portable/Simplification/CSharpParenthesesReducer.Rewriter.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpParenthesesReducer.Rewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Options;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpParenthesesReducer
     {
-        private class Rewriter : AbstractExpressionRewriter
+        private class Rewriter : AbstractReductionRewriter
         {
-            public Rewriter(OptionSet optionSet, CancellationToken cancellationToken)
-                : base(optionSet, cancellationToken)
+            public Rewriter(ObjectPool<IReductionRewriter> pool)
+                : base(pool)
             {
             }
 

src/Workspaces/CSharp/Portable/Simplification/CSharpParenthesesReducer.cs → src/Workspaces/CSharp/Portable/Simplification/Reducers/CSharpParenthesesReducer.cs

@@ -8,14 +8,17 @@
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Simplification;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Simplification
 {
     internal partial class CSharpParenthesesReducer : AbstractCSharpReducer
     {
-        public override IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken)
+        private static readonly ObjectPool<IReductionRewriter> s_pool = new ObjectPool<IReductionRewriter>(
+            () => new Rewriter(s_pool));
+
+        public CSharpParenthesesReducer() : base(s_pool)
         {
-            return new Rewriter(optionSet, cancellationToken);
         }
 
         private static readonly Func<ParenthesizedExpressionSyntax, SemanticModel, OptionSet, CancellationToken, SyntaxNode> s_simplifyParentheses = SimplifyParentheses;

src/Workspaces/Core/Portable/Simplification/AbstractReducer.IExpressionRewriter.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System;
+using System.Threading;
+using Microsoft.CodeAnalysis.Options;
+
 namespace Microsoft.CodeAnalysis.Simplification
 {
     internal abstract partial class AbstractReducer
     {
-        internal interface IExpressionRewriter
+        internal interface IReductionRewriter : IDisposable
         {
+            void Initialize(OptionSet optionSet, CancellationToken cancellationToken);
+
             SyntaxNodeOrToken VisitNodeOrToken(SyntaxNodeOrToken nodeOrTokenToReduce, SemanticModel semanticModel, bool simplifyAllDescendants);
 
             bool HasMoreWork { get; }
         }
     }
-}
+}
\ No newline at end of file

src/Workspaces/Core/Portable/Simplification/AbstractReducer.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Threading;
-using Microsoft.CodeAnalysis.Options;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Simplification
 {
     internal abstract partial class AbstractReducer
     {
-        public abstract IExpressionRewriter CreateExpressionRewriter(OptionSet optionSet, CancellationToken cancellationToken);
+        private readonly ObjectPool<IReductionRewriter> _pool;
+
+        protected AbstractReducer(ObjectPool<IReductionRewriter> pool)
+            => _pool = pool;
+
+        public IReductionRewriter GetOrCreateRewriter()
+            => _pool.Allocate();
     }
-}
+}
\ No newline at end of file

src/Workspaces/Core/Portable/Simplification/AbstractSimplificationService.cs

@@ -163,7 +163,7 @@ protected virtual SyntaxNode TransformReducedNode(SyntaxNode reducedNode, Syntax
             Document document,
             SyntaxNode root,
             ImmutableArray<NodeOrTokenToReduce> nodesAndTokensToReduce,
-            IEnumerable<AbstractReducer> reducers,
+            ImmutableArray<AbstractReducer> reducers,
             OptionSet optionSet,
             SemanticModel semanticModel,
             ConcurrentDictionary<SyntaxNode, SyntaxNode> reducedNodesMap,
@@ -178,89 +178,92 @@ protected virtual SyntaxNode TransformReducedNode(SyntaxNode reducedNode, Syntax
             {
                 var nodeOrTokenToReduce = nodesAndTokensToReduce[i];
                 simplifyTasks[i] = Task.Run(async () =>
-            {
-                var nodeOrToken = nodeOrTokenToReduce.OriginalNodeOrToken;
-                var simplifyAllDescendants = nodeOrTokenToReduce.SimplifyAllDescendants;
-                var semanticModelForReduce = semanticModel;
-                var currentNodeOrToken = nodeOrTokenToReduce.NodeOrToken;
-                var isNode = nodeOrToken.IsNode;
-
-                foreach (var reducer in reducers)
                 {
-                    cancellationToken.ThrowIfCancellationRequested();
+                    var nodeOrToken = nodeOrTokenToReduce.OriginalNodeOrToken;
+                    var simplifyAllDescendants = nodeOrTokenToReduce.SimplifyAllDescendants;
+                    var semanticModelForReduce = semanticModel;
+                    var currentNodeOrToken = nodeOrTokenToReduce.NodeOrToken;
+                    var isNode = nodeOrToken.IsNode;
 
-                    var rewriter = reducer.CreateExpressionRewriter(optionSet, cancellationToken);
-
-                    do
+                    foreach (var reducer in reducers)
                     {
-                        if (currentNodeOrToken.SyntaxTree != semanticModelForReduce.SyntaxTree)
-                        {
-                            // currentNodeOrToken was simplified either by a previous reducer or
-                            // a previous iteration of the current reducer.
-                            // Create a speculative semantic model for the simplified node for semantic queries.
-
-                            // Certain node kinds (expressions/statements) require non-null parent nodes during simplification.
-                            // However, the reduced nodes haven't been parented yet, so do the required parenting using the original node's parent.
-                            if (currentNodeOrToken.Parent == null &&
-                                nodeOrToken.Parent != null &&
-                                (currentNodeOrToken.IsToken ||
-                                currentNodeOrToken.AsNode() is TExpressionSyntax ||
-                                currentNodeOrToken.AsNode() is TStatementSyntax ||
-                                currentNodeOrToken.AsNode() is TCrefSyntax))
-                            {
-                                var annotation = new SyntaxAnnotation();
-                                currentNodeOrToken = currentNodeOrToken.WithAdditionalAnnotations(annotation);
+                        cancellationToken.ThrowIfCancellationRequested();
 
-                                var replacedParent = isNode ?
-                                    nodeOrToken.Parent.ReplaceNode(nodeOrToken.AsNode(), currentNodeOrToken.AsNode()) :
-                                    nodeOrToken.Parent.ReplaceToken(nodeOrToken.AsToken(), currentNodeOrToken.AsToken());
-
-                                currentNodeOrToken = replacedParent
-                                    .ChildNodesAndTokens()
-                                    .Single((c) => c.HasAnnotation(annotation));
-                            }
+                        using (var rewriter = reducer.GetOrCreateRewriter())
+                        {
+                            rewriter.Initialize(optionSet, cancellationToken);
 
-                            if (isNode)
+                            do
                             {
-                                var currentNode = currentNodeOrToken.AsNode();
-                                if (this.CanNodeBeSimplifiedWithoutSpeculation(nodeOrToken.AsNode()))
-                                {
-                                    // Since this node cannot be speculated, we are replacing the Document with the changes and get a new SemanticModel
-                                    SyntaxAnnotation marker = new SyntaxAnnotation();
-                                    var newRoot = root.ReplaceNode(nodeOrToken.AsNode(), currentNode.WithAdditionalAnnotations(marker));
-                                    var newDocument = document.WithSyntaxRoot(newRoot);
-                                    semanticModelForReduce = await newDocument.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
-                                    newRoot = await semanticModelForReduce.SyntaxTree.GetRootAsync(cancellationToken).ConfigureAwait(false);
-                                    currentNodeOrToken = newRoot.DescendantNodes().Single((c) => c.HasAnnotation(marker));
-                                }
-                                else
+                                if (currentNodeOrToken.SyntaxTree != semanticModelForReduce.SyntaxTree)
                                 {
-                                    // Create speculative semantic model for simplified node.
-                                    semanticModelForReduce = GetSpeculativeSemanticModel(ref currentNode, semanticModel, nodeOrToken.AsNode());
-                                    currentNodeOrToken = currentNode;
+                                    // currentNodeOrToken was simplified either by a previous reducer or
+                                    // a previous iteration of the current reducer.
+                                    // Create a speculative semantic model for the simplified node for semantic queries.
+
+                                    // Certain node kinds (expressions/statements) require non-null parent nodes during simplification.
+                                    // However, the reduced nodes haven't been parented yet, so do the required parenting using the original node's parent.
+                                    if (currentNodeOrToken.Parent == null &&
+                                        nodeOrToken.Parent != null &&
+                                        (currentNodeOrToken.IsToken ||
+                                        currentNodeOrToken.AsNode() is TExpressionSyntax ||
+                                        currentNodeOrToken.AsNode() is TStatementSyntax ||
+                                        currentNodeOrToken.AsNode() is TCrefSyntax))
+                                    {
+                                        var annotation = new SyntaxAnnotation();
+                                        currentNodeOrToken = currentNodeOrToken.WithAdditionalAnnotations(annotation);
+
+                                        var replacedParent = isNode ?
+                                            nodeOrToken.Parent.ReplaceNode(nodeOrToken.AsNode(), currentNodeOrToken.AsNode()) :
+                                            nodeOrToken.Parent.ReplaceToken(nodeOrToken.AsToken(), currentNodeOrToken.AsToken());
+
+                                        currentNodeOrToken = replacedParent
+                                            .ChildNodesAndTokens()
+                                            .Single((c) => c.HasAnnotation(annotation));
+                                    }
+
+                                    if (isNode)
+                                    {
+                                        var currentNode = currentNodeOrToken.AsNode();
+                                        if (this.CanNodeBeSimplifiedWithoutSpeculation(nodeOrToken.AsNode()))
+                                        {
+                                            // Since this node cannot be speculated, we are replacing the Document with the changes and get a new SemanticModel
+                                            SyntaxAnnotation marker = new SyntaxAnnotation();
+                                            var newRoot = root.ReplaceNode(nodeOrToken.AsNode(), currentNode.WithAdditionalAnnotations(marker));
+                                            var newDocument = document.WithSyntaxRoot(newRoot);
+                                            semanticModelForReduce = await newDocument.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+                                            newRoot = await semanticModelForReduce.SyntaxTree.GetRootAsync(cancellationToken).ConfigureAwait(false);
+                                            currentNodeOrToken = newRoot.DescendantNodes().Single((c) => c.HasAnnotation(marker));
+                                        }
+                                        else
+                                        {
+                                            // Create speculative semantic model for simplified node.
+                                            semanticModelForReduce = GetSpeculativeSemanticModel(ref currentNode, semanticModel, nodeOrToken.AsNode());
+                                            currentNodeOrToken = currentNode;
+                                        }
+                                    }
                                 }
+
+                                // Reduce the current node or token.
+                                currentNodeOrToken = rewriter.VisitNodeOrToken(currentNodeOrToken, semanticModelForReduce, simplifyAllDescendants);
                             }
+                            while (rewriter.HasMoreWork);
                         }
-
-                        // Reduce the current node or token.
-                        currentNodeOrToken = rewriter.VisitNodeOrToken(currentNodeOrToken, semanticModelForReduce, simplifyAllDescendants);
                     }
-                    while (rewriter.HasMoreWork);
-                }
 
-                // If nodeOrToken was simplified, add it to the appropriate dictionary of replaced nodes/tokens.
-                if (currentNodeOrToken != nodeOrToken)
-                {
-                    if (isNode)
-                    {
-                        reducedNodesMap[nodeOrToken.AsNode()] = currentNodeOrToken.AsNode();
-                    }
-                    else
+                    // If nodeOrToken was simplified, add it to the appropriate dictionary of replaced nodes/tokens.
+                    if (currentNodeOrToken != nodeOrToken)
                     {
-                        reducedTokensMap[nodeOrToken.AsToken()] = currentNodeOrToken.AsToken();
+                        if (isNode)
+                        {
+                            reducedNodesMap[nodeOrToken.AsNode()] = currentNodeOrToken.AsNode();
+                        }
+                        else
+                        {
+                            reducedTokensMap[nodeOrToken.AsToken()] = currentNodeOrToken.AsToken();
+                        }
                     }
-                }
-            }, cancellationToken);
+                }, cancellationToken);
             }
 
             return Task.WhenAll(simplifyTasks);

src/Workspaces/VisualBasic/Portable/BasicWorkspace.vbproj

@@ -184,29 +184,29 @@
     <Compile Include="Rename\LocalConflictVisitor.vb" />
     <Compile Include="Rename\VisualBasicRenameRewriterLanguageService.vb" />
     <Compile Include="Rename\VisualBasicRenameRewriterLanguageServiceFactory.vb" />
-    <Compile Include="Simplification\AbstractVisualBasicReducer.vb" />
-    <Compile Include="Simplification\AbstractVisualBasicSimplifier.AbstractExpressionRewriter.vb" />
-    <Compile Include="Simplification\VisualBasicCallReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicCallReducer.vb" />
-    <Compile Include="Simplification\VisualBasicCastReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicCastReducer.vb" />
-    <Compile Include="Simplification\VisualBasicInferredMemberNameReducer.vb" />
-    <Compile Include="Simplification\VisualBasicInferredMemberNameReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicEscapingReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicEscapingReducer.vb" />
-    <Compile Include="Simplification\VisualBasicExtensionMethodReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicExtensionMethodReducer.vb" />
-    <Compile Include="Simplification\VisualBasicMiscellaneousReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicMiscellaneousReducer.vb" />
-    <Compile Include="Simplification\VisualBasicNameReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicNameReducer.vb" />
-    <Compile Include="Simplification\VisualBasicParenthesesReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicParenthesesReducer.vb" />
+    <Compile Include="Simplification\Reducers\AbstractVisualBasicReducer.AbstractReductionRewriter.vb" />
+    <Compile Include="Simplification\Reducers\AbstractVisualBasicReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicCallReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicCallReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicCastReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicCastReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicInferredMemberNameReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicInferredMemberNameReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicEscapingReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicEscapingReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicExtensionMethodReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicExtensionMethodReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicMiscellaneousReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicMiscellaneousReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicNameReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicNameReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicParenthesesReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicParenthesesReducer.vb" />
     <Compile Include="Simplification\VisualBasicSimplificationService.Expander.vb" />
     <Compile Include="Simplification\VisualBasicSimplificationService.NodesAndTokensToReduceComputer.vb" />
     <Compile Include="Simplification\VisualBasicSimplificationService.vb" />
-    <Compile Include="Simplification\VisualBasicVariableDeclaratorReducer.Rewriter.vb" />
-    <Compile Include="Simplification\VisualBasicVariableDeclaratorReducer.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicVariableDeclaratorReducer.Rewriter.vb" />
+    <Compile Include="Simplification\Reducers\VisualBasicVariableDeclaratorReducer.vb" />
     <Compile Include="Utilities\DirectiveSyntaxEqualityComparer.vb" />
     <Compile Include="Utilities\DirectiveWalker.vb" />
     <Compile Include="Utilities\ImportsClauseComparer.vb" />

src/Workspaces/VisualBasic/Portable/Simplification/AbstractVisualBasicSimplifier.AbstractExpressionRewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/AbstractVisualBasicReducer.AbstractReductionRewriter.vb

@@ -7,25 +7,43 @@ Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend MustInherit Class AbstractVisualBasicReducer
-        Friend MustInherit Class AbstractExpressionRewriter
+        Friend MustInherit Class AbstractReductionRewriter
             Inherits VisualBasicSyntaxRewriter
-            Implements IExpressionRewriter
+            Implements IReductionRewriter
+
+            Private ReadOnly _pool As ObjectPool(Of IReductionRewriter)
+
+            Protected CancellationToken As CancellationToken
+            Private _simplificationOptions As OptionSet
+
+            Private ReadOnly _processedParentNodes As HashSet(Of SyntaxNode) = New HashSet(Of SyntaxNode)()
+            Private _semanticModel As SemanticModel
 
-            Protected ReadOnly CancellationToken As CancellationToken
-            Private ReadOnly _processedParentNodes As HashSet(Of SyntaxNode)
             Private _hasMoreWork As Boolean
             Protected _alwaysSimplify As Boolean
-            Private ReadOnly _simplificationOptions As OptionSet
-            Private _semanticModel As SemanticModel
 
-            Protected Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New()
-                Me.CancellationToken = cancellationToken
-                Me._simplificationOptions = optionSet
-                _processedParentNodes = New HashSet(Of SyntaxNode)
+            Protected Sub New(pool As ObjectPool(Of IReductionRewriter))
+                _pool = pool
+            End Sub
+
+            Public Sub Initialize(optionSet As OptionSet, cancellationToken As CancellationToken) Implements IReductionRewriter.Initialize
+                _simplificationOptions = optionSet
+                cancellationToken = cancellationToken
+            End Sub
+
+            Public Sub Dispose() Implements IDisposable.Dispose
+                _simplificationOptions = Nothing
+                CancellationToken = CancellationToken.None
+                _processedParentNodes.Clear()
+                _semanticModel = Nothing
+
+                _hasMoreWork = False
+                _alwaysSimplify = False
+
+                _pool.Free(Me)
             End Sub
 
-            Public ReadOnly Property HasMoreWork As Boolean Implements IExpressionRewriter.HasMoreWork
+            Public ReadOnly Property HasMoreWork As Boolean Implements IReductionRewriter.HasMoreWork
                 Get
                     Return _hasMoreWork
                 End Get
@@ -140,8 +158,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
                 Return SimplifyNode(statement, newNode, GetParentNode(statement), simplifier)
             End Function
 
-            Public Function VisitNodeOrToken(nodeOrToken As SyntaxNodeOrToken, semanticModel As SemanticModel, simplifyAllDescendants As Boolean) As SyntaxNodeOrToken Implements IExpressionRewriter.VisitNodeOrToken
-                _semanticModel = DirectCast(semanticModel, semanticModel)
+            Public Function VisitNodeOrToken(nodeOrToken As SyntaxNodeOrToken, semanticModel As SemanticModel, simplifyAllDescendants As Boolean) As SyntaxNodeOrToken Implements IReductionRewriter.VisitNodeOrToken
+                _semanticModel = DirectCast(semanticModel, SemanticModel)
                 _alwaysSimplify = simplifyAllDescendants
                 _hasMoreWork = False
                 _processedParentNodes.Clear()
@@ -186,4 +204,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             End Function
         End Class
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/AbstractVisualBasicReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/AbstractVisualBasicReducer.vb

@@ -9,6 +9,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend MustInherit Class AbstractVisualBasicReducer
         Inherits AbstractReducer
 
+        Protected Sub New(pool As ObjectPool(Of IReductionRewriter))
+            MyBase.New(pool)
+        End Sub
+
         Protected Shared ReadOnly s_reduceParentheses As Func(Of ParenthesizedExpressionSyntax, SemanticModel, OptionSet, CancellationToken, SyntaxNode) = AddressOf ReduceParentheses
 
         Protected Shared Function ReduceParentheses(

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicCallReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicCallReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicCallReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitCallStatement(node As CallStatementSyntax) As SyntaxNode

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicCallReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicCallReducer.vb

@@ -9,9 +9,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicCallReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Shared ReadOnly s_simplifyCallStatement As Func(Of CallStatementSyntax, SemanticModel, OptionSet, CancellationToken, SyntaxNode) = AddressOf SimplifyCallStatement
 
@@ -36,6 +39,5 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             ' We don't know how to simplify this.
             Return callStatement
         End Function
-
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicCastReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicCastReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicCastReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitCTypeExpression(node As CTypeExpressionSyntax) As SyntaxNode

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicCastReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicCastReducer.vb

@@ -9,9 +9,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicCastReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Overloads Shared Function SimplifyCast(
             castNode As ExpressionSyntax,

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicEscapingReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicEscapingReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicEscapingReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitToken(token As SyntaxToken) As SyntaxToken
@@ -20,7 +19,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
                     newToken:=MyBase.VisitToken(token),
                     simplifyFunc:=AddressOf TryUnescapeToken)
             End Function
-
         End Class
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicEscapingReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicEscapingReducer.vb

@@ -3,17 +3,18 @@
 Imports System.Threading
 Imports Microsoft.CodeAnalysis
 Imports Microsoft.CodeAnalysis.Options
-Imports Microsoft.CodeAnalysis.Simplification
-Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicEscapingReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New VisualBasicEscapingReducer.Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Shared Function TryUnescapeToken(identifier As SyntaxToken, semanticModel As SemanticModel, optionSet As OptionSet, cancellationToken As CancellationToken) As SyntaxToken
             If Not identifier.IsBracketed Then
@@ -216,4 +217,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             Return False
         End Function
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicExtensionMethodReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicExtensionMethodReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicExtensionMethodReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitInvocationExpression(node As InvocationExpressionSyntax) As SyntaxNode

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicExtensionMethodReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicExtensionMethodReducer.vb

@@ -8,9 +8,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicExtensionMethodReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Shared ReadOnly s_simplifyInvocationExpression As Func(Of InvocationExpressionSyntax, SemanticModel, OptionSet, CancellationToken, SyntaxNode) = AddressOf SimplifyInvocationExpression
 
@@ -61,6 +64,5 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
 
             Return rewrittenNode
         End Function
-
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicInferredMemberNameReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicInferredMemberNameReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicInferredMemberNameReducer
 
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitSimpleArgument(node As SimpleArgumentSyntax) As SyntaxNode
@@ -41,4 +40,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             End Function
         End Class
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicInferredMemberNameReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicInferredMemberNameReducer.vb

@@ -14,9 +14,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicInferredMemberNameReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New VisualBasicInferredMemberNameReducer.Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Shared ReadOnly s_simplifyTupleName As Func(Of SimpleArgumentSyntax, SemanticModel, OptionSet, CancellationToken, SimpleArgumentSyntax) = AddressOf SimplifyTupleName
 
@@ -56,4 +59,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             Return SyntaxFactory.InferredFieldInitializer(node.Expression).WithTriviaFrom(node)
         End Function
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicMiscellaneousReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicMiscellaneousReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicMiscellaneousReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitInvocationExpression(node As InvocationExpressionSyntax) As SyntaxNode

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicMiscellaneousReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicMiscellaneousReducer.vb

@@ -9,9 +9,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicMiscellaneousReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Shared ReadOnly s_simplifyParameter As Func(Of ParameterSyntax, SemanticModel, OptionSet, CancellationToken, ParameterSyntax) = AddressOf SimplifyParameter
 
@@ -75,6 +78,5 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             ' We don't know how to simplify this.
             Return objectCreationExpression
         End Function
-
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicNameReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicNameReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 Imports Microsoft.CodeAnalysis.Simplification
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicNameReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitGenericName(node As GenericNameSyntax) As SyntaxNode
@@ -109,7 +107,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
 
                 Return result
             End Function
-
         End Class
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicNameReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicNameReducer.vb

@@ -12,9 +12,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicNameReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Shared ReadOnly s_simplifyName As Func(Of ExpressionSyntax, SemanticModel, OptionSet, CancellationToken, SyntaxNode) = AddressOf SimplifyName
 
@@ -39,6 +42,5 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             node = node.CopyAnnotationsTo(replacementNode).WithAdditionalAnnotations(Formatter.Annotation)
             Return node.WithoutAnnotations(Simplifier.Annotation)
         End Function
-
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicParenthesesReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicParenthesesReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicParenthesesReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitParenthesizedExpression(node As ParenthesizedExpressionSyntax) As SyntaxNode

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicParenthesesReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicParenthesesReducer.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
-
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicParenthesesReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
 
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicVariableDeclaratorReducer.Rewriter.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicVariableDeclaratorReducer.Rewriter.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-Imports Microsoft.CodeAnalysis.Simplification
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
-Imports System.Threading
-Imports Microsoft.CodeAnalysis.Options
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicVariableDeclaratorReducer
         Private Class Rewriter
-            Inherits AbstractExpressionRewriter
+            Inherits AbstractReductionRewriter
 
-            Public Sub New(optionSet As OptionSet, cancellationToken As CancellationToken)
-                MyBase.New(optionSet, cancellationToken)
+            Public Sub New(pool As ObjectPool(Of IReductionRewriter))
+                MyBase.New(pool)
             End Sub
 
             Public Overrides Function VisitVariableDeclarator(node As VariableDeclaratorSyntax) As SyntaxNode
@@ -23,4 +20,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             End Function
         End Class
     End Class
-End Namespace
+End Namespace
\ No newline at end of file

src/Workspaces/VisualBasic/Portable/Simplification/VisualBasicVariableDeclaratorReducer.vb → src/Workspaces/VisualBasic/Portable/Simplification/Reducers/VisualBasicVariableDeclaratorReducer.vb

@@ -11,9 +11,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
     Partial Friend Class VisualBasicVariableDeclaratorReducer
         Inherits AbstractVisualBasicReducer
 
-        Public Overrides Function CreateExpressionRewriter(optionSet As OptionSet, cancellationToken As CancellationToken) As IExpressionRewriter
-            Return New Rewriter(optionSet, cancellationToken)
-        End Function
+        Private Shared ReadOnly s_pool As ObjectPool(Of IReductionRewriter) =
+            New ObjectPool(Of IReductionRewriter)(Function() New Rewriter(s_pool))
+
+        Public Sub New()
+            MyBase.New(s_pool)
+        End Sub
 
         Private Shared ReadOnly s_simplifyVariableDeclarator As Func(Of VariableDeclaratorSyntax, SemanticModel, OptionSet, CancellationToken, SyntaxNode) = AddressOf SimplifyVariableDeclarator
 
@@ -39,5 +42,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Simplification
             Return replacementNode.WithoutAnnotations(Simplifier.Annotation)
         End Function
     End Class
-End Namespace
-
+End Namespace
\ No newline at end of file