Merge pull request #14049 from CyrusNajmabadi/poolArrayBuilders

Pool array builders so we produce less garbage.

src/EditorFeatures/CSharpTest/CodeActions/MoveType/CSharpMoveTypeTestsBase.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.Tasks;
-using Microsoft.CodeAnalysis.CodeRefactorings;
-using Microsoft.CodeAnalysis.CodeRefactorings.MoveType;
 using Microsoft.CodeAnalysis.Editor.UnitTests.MoveType;
 using Microsoft.CodeAnalysis.Editor.UnitTests.Workspaces;
 
@@ -27,4 +25,4 @@ protected override string GetLanguage()
             return LanguageNames.CSharp;
         }
     }
-}
+}
\ No newline at end of file

src/EditorFeatures/Core/Implementation/CodeFixes/CodeFixService.ProjectCodeFixProvider.cs

@@ -46,7 +46,7 @@ private ImmutableArray<CodeFixProvider> CreateFixers(string language)
                 }
 
                 IEnumerable<TypeInfo> typeInfos = null;
-                ImmutableArray<CodeFixProvider>.Builder builder = null;
+                var builder = ArrayBuilder<CodeFixProvider>.GetInstance();
 
                 try
                 {
@@ -66,7 +66,6 @@ private ImmutableArray<CodeFixProvider> CreateFixers(string language)
                                         attribute.Languages.Length == 0 ||
                                         attribute.Languages.Contains(language))
                                     {
-                                        builder = builder ?? ImmutableArray.CreateBuilder<CodeFixProvider>();
                                         builder.Add((CodeFixProvider)Activator.CreateInstance(typeInfo.AsType()));
                                     }
                                 }
@@ -83,7 +82,7 @@ private ImmutableArray<CodeFixProvider> CreateFixers(string language)
                     // NOTE: We could report "unable to load analyzer" exception here but it should have been already reported by DiagnosticService.
                 }
 
-                return builder != null ? builder.ToImmutable() : ImmutableArray<CodeFixProvider>.Empty;
+                return builder.ToImmutableAndFree();
             }
         }
     }

src/EditorFeatures/Core/Implementation/Diagnostics/AbstractDiagnosticsTaggerProvider.AggregatingTagger.cs

@@ -117,7 +117,7 @@ private class AggregatingTagger : ForegroundThreadAffinitizedObject, IAccurateTa
 
                 // GetDiagnostics returns whatever cached diagnostics in the service which can be stale ones. for example, build error will be most likely stale
                 // diagnostics. so here we make sure we filter out any diagnostics that is not in the text range.
-                var builder = ImmutableArray.CreateBuilder<DiagnosticData>();
+                var builder = ArrayBuilder<DiagnosticData>.GetInstance();
                 var fullSpan = new TextSpan(0, text.Length);
                 foreach (var diagnostic in _owner._diagnosticService.GetDiagnostics(
                     args.Workspace, args.ProjectId, args.DocumentId, args.Id, includeSuppressedDiagnostics: false, cancellationToken: cancellationToken))
@@ -128,7 +128,7 @@ private class AggregatingTagger : ForegroundThreadAffinitizedObject, IAccurateTa
                     }
                 }
 
-                return builder.ToImmutable();
+                return builder.ToImmutableAndFree();
             }
 
             public void OnTaggerCreated()

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/FileSystem/FileSystemCompletionHelper.cs

@@ -86,7 +86,7 @@ private CompletionItem CreateNetworkRoot(TextSpan textChangeSpan)
 
         private ImmutableArray<CompletionItem> GetFilesAndDirectories(string path, string basePath)
         {
-            var result = ImmutableArray.CreateBuilder<CompletionItem>();
+            var result = ArrayBuilder<CompletionItem>.GetInstance();
             var pathKind = PathUtilities.GetPathKind(path);
             switch (pathKind)
             {
@@ -164,7 +164,7 @@ private ImmutableArray<CompletionItem> GetFilesAndDirectories(string path, strin
                     throw ExceptionUtilities.Unreachable;
             }
 
-            return result.AsImmutable();
+            return result.ToImmutableAndFree();
         }
 
         private static bool IsDriveRoot(string fullPath)

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Model.cs

@@ -138,13 +138,13 @@ internal class Model
                 // the description if necessary. We won't do this if the list was triggered to show
                 // snippet shortcuts.
 
-                var totalItemsBuilder = ImmutableArray.CreateBuilder<PresentationItem>();
+                var totalItemsBuilder = ArrayBuilder<PresentationItem>.GetInstance();
                 foreach (var item in originalList.Items)
                 {
                     totalItemsBuilder.Add(new DescriptionModifyingPresentationItem(item, completionService));
                 }
 
-                totalItems = totalItemsBuilder.AsImmutable();
+                totalItems = totalItemsBuilder.ToImmutableAndFree();
                 defaultSuggestionModePresentationItem = new DescriptionModifyingPresentationItem(
                     CreateDefaultSuggestionModeItem(), completionService, isSuggestionModeItem: true);
                 suggestionModePresentationItem = suggestionModeItem != null ? new DescriptionModifyingPresentationItem(suggestionModeItem, completionService, isSuggestionModeItem: true) : null;

src/EditorFeatures/Core/Implementation/NavigateTo/NavigateToSearchResultProvider.cs

@@ -47,7 +47,7 @@ internal sealed partial class NavigateToSearchResultProvider : INavigateToSearch
         {
             using (var patternMatcher = new PatternMatcher(pattern, allowFuzzyMatching: true))
             {
-                var result = ImmutableArray.CreateBuilder<ValueTuple<DeclaredSymbolInfo, Document, IEnumerable<PatternMatch>>>();
+                var result = ArrayBuilder<ValueTuple<DeclaredSymbolInfo, Document, IEnumerable<PatternMatch>>>.GetInstance();
                 foreach (var document in project.Documents)
                 {
                     if (searchDocument != null && document != searchDocument)
@@ -73,7 +73,7 @@ internal sealed partial class NavigateToSearchResultProvider : INavigateToSearch
                     }
                 }
 
-                return result.ToImmutable();
+                return result.ToImmutableAndFree();
             }
         }
 

src/EditorFeatures/Core/Implementation/Structure/AbstractStructureTaggerProvider.cs

@@ -213,7 +213,7 @@ protected sealed override ITaggerEventSource CreateEventSource(ITextView textVie
             ImmutableArray<BlockSpan> regions, ITextSnapshot snapshot)
         {
             // Remove any spans that aren't multiline.
-            var multiLineRegions = ImmutableArray.CreateBuilder<BlockSpan>();
+            var multiLineRegions = ArrayBuilder<BlockSpan>.GetInstance();
             foreach (var region in regions)
             {
                 if (region != null && region.TextSpan.Length > 0)
@@ -254,7 +254,7 @@ protected sealed override ITaggerEventSource CreateEventSource(ITextView textVie
             // Note we pass a IComparer instead of a Comparison to work around this
             // issue in ImmutableArray.Builder: https://github.com/dotnet/corefx/issues/11173
             multiLineRegions.Sort(s_blockSpanComparer);
-            return multiLineRegions.ToImmutable();
+            return multiLineRegions.ToImmutableAndFree();
         }
     }
 }
\ No newline at end of file

src/EditorFeatures/Core/Implementation/Suggestions/CodeFixSuggestedAction.cs

@@ -64,7 +64,7 @@ internal class CodeFixSuggestedAction : SuggestedActionWithFlavors, ITelemetryDi
                 return null;
             }
 
-            var fixAllSuggestedActions = ImmutableArray.CreateBuilder<FixAllSuggestedAction>();
+            var fixAllSuggestedActions = ArrayBuilder<FixAllSuggestedAction>.GetInstance();
             foreach (var scope in supportedScopes)
             {
                 var fixAllStateForScope = fixAllState.WithScopeAndEquivalenceKey(scope, action.EquivalenceKey);
@@ -75,7 +75,9 @@ internal class CodeFixSuggestedAction : SuggestedActionWithFlavors, ITelemetryDi
                 fixAllSuggestedActions.Add(fixAllSuggestedAction);
             }
 
-            return new SuggestedActionSet(fixAllSuggestedActions.ToImmutable(), title: EditorFeaturesResources.Fix_all_occurrences_in);
+            return new SuggestedActionSet(
+                fixAllSuggestedActions.ToImmutableAndFree(),
+                title: EditorFeaturesResources.Fix_all_occurrences_in);
         }
 
         public string GetDiagnosticID()

src/EditorFeatures/Core/Implementation/Suggestions/SuggestedActionWithFlavors.cs

@@ -61,7 +61,7 @@ public async override Task<IEnumerable<SuggestedActionSet>> GetActionSetsAsync(C
 
                 _actionSets = await extensionManager.PerformFunctionAsync(Provider, async () =>
                 {
-                    var builder = ImmutableArray.CreateBuilder<SuggestedActionSet>();
+                    var builder = ArrayBuilder<SuggestedActionSet>.GetInstance();
 
                     // We use ConfigureAwait(true) to stay on the UI thread.
                     var previewChangesSuggestedActionSet = await GetPreviewChangesSuggestedActionSetAsync(cancellationToken).ConfigureAwait(true);
@@ -78,7 +78,7 @@ public async override Task<IEnumerable<SuggestedActionSet>> GetActionSetsAsync(C
                         builder.Add(fixAllSuggestedActionSet);
                     }
 
-                    return builder.ToImmutable();
+                    return builder.ToImmutableAndFree();
                     // We use ConfigureAwait(true) to stay on the UI thread.
                 }, defaultValue: ImmutableArray<SuggestedActionSet>.Empty).ConfigureAwait(true);
             }

src/EditorFeatures/Core/Implementation/Suggestions/SuggestedActionsSourceProvider.cs

@@ -324,13 +324,13 @@ private CodeRefactoring FilterOnUIThread(CodeRefactoring refactoring, Workspace
             private IEnumerable<SuggestedActionSet> OrganizeFixes(Workspace workspace, IEnumerable<CodeFixCollection> fixCollections, bool hasSuppressionFixes)
             {
                 var map = ImmutableDictionary.CreateBuilder<CodeFixGroupKey, IList<SuggestedAction>>();
-                var order = ImmutableArray.CreateBuilder<CodeFixGroupKey>();
+                var order = ArrayBuilder<CodeFixGroupKey>.GetInstance();
 
                 // First group fixes by diagnostic and priority.
                 GroupFixes(workspace, fixCollections, map, order, hasSuppressionFixes);
 
                 // Then prioritize between the groups.
-                return PrioritizeFixGroups(map.ToImmutable(), order.ToImmutable());
+                return PrioritizeFixGroups(map.ToImmutable(), order.ToImmutableAndFree());
             }
 
             /// <summary>
@@ -340,7 +340,7 @@ private IEnumerable<SuggestedActionSet> OrganizeFixes(Workspace workspace, IEnum
                 Workspace workspace,
                 IEnumerable<CodeFixCollection> fixCollections,
                 IDictionary<CodeFixGroupKey, IList<SuggestedAction>> map,
-                IList<CodeFixGroupKey> order,
+                ArrayBuilder<CodeFixGroupKey> order,
                 bool hasSuppressionFixes)
             {
                 foreach (var fixCollection in fixCollections)
@@ -417,7 +417,10 @@ private IEnumerable<SuggestedActionSet> OrganizeFixes(Workspace workspace, IEnum
                 }
             }
 
-            private static void AddFix(CodeFix fix, SuggestedAction suggestedAction, IDictionary<CodeFixGroupKey, IList<SuggestedAction>> map, IList<CodeFixGroupKey> order)
+            private static void AddFix(
+                CodeFix fix, SuggestedAction suggestedAction,
+                IDictionary<CodeFixGroupKey, IList<SuggestedAction>> map,
+                ArrayBuilder<CodeFixGroupKey> order)
             {
                 var diag = fix.GetPrimaryDiagnosticData();
 
@@ -443,7 +446,7 @@ private static void AddFix(CodeFix fix, SuggestedAction suggestedAction, IDictio
             /// </remarks>
             private static IEnumerable<SuggestedActionSet> PrioritizeFixGroups(IDictionary<CodeFixGroupKey, IList<SuggestedAction>> map, IList<CodeFixGroupKey> order)
             {
-                var sets = ImmutableArray.CreateBuilder<SuggestedActionSet>();
+                var sets = ArrayBuilder<SuggestedActionSet>.GetInstance();
 
                 foreach (var diag in order)
                 {
@@ -459,7 +462,7 @@ private static IEnumerable<SuggestedActionSet> PrioritizeFixGroups(IDictionary<C
                     }
                 }
 
-                return sets.ToImmutable();
+                return sets.ToImmutableAndFree();
             }
 
             private static SuggestedActionSetPriority GetSuggestedActionSetPriority(CodeActionPriority key)
@@ -527,7 +530,7 @@ private static SuggestedActionSetPriority GetSuggestedActionSetPriority(CodeActi
             /// </remarks>
             private SuggestedActionSet OrganizeRefactorings(Workspace workspace, CodeRefactoring refactoring)
             {
-                var refactoringSuggestedActions = ImmutableArray.CreateBuilder<SuggestedAction>();
+                var refactoringSuggestedActions = ArrayBuilder<SuggestedAction>.GetInstance();
 
                 foreach (var a in refactoring.Actions)
                 {
@@ -536,7 +539,8 @@ private SuggestedActionSet OrganizeRefactorings(Workspace workspace, CodeRefacto
                         a, refactoring.Provider, _owner._listener));
                 }
 
-                return new SuggestedActionSet(refactoringSuggestedActions.ToImmutable(), SuggestedActionSetPriority.Low);
+                return new SuggestedActionSet(
+                    refactoringSuggestedActions.ToImmutableAndFree(), SuggestedActionSetPriority.Low);
             }
 
             public async Task<bool> HasSuggestedActionsAsync(ISuggestedActionCategorySet requestedActionCategories, SnapshotSpan range, CancellationToken cancellationToken)

src/EditorFeatures/Core/Implementation/Suggestions/SuppressionSuggestedAction.cs

@@ -66,7 +66,7 @@ public override Task<IEnumerable<SuggestedActionSet>> GetActionSetsAsync(Cancell
 
             if (this.CodeAction.GetCodeActions().Any())
             {
-                var nestedSuggestedActions = ImmutableArray.CreateBuilder<SuggestedAction>();
+                var nestedSuggestedActions = ArrayBuilder<SuggestedAction>.GetInstance();
                 var fixCount = this.CodeAction.GetCodeActions().Length;
 
                 foreach (var c in this.CodeAction.GetCodeActions())
@@ -80,7 +80,7 @@ public override Task<IEnumerable<SuggestedActionSet>> GetActionSetsAsync(Cancell
                 }
 
                 _actionSets = ImmutableArray.Create(
-                    new SuggestedActionSet(nestedSuggestedActions.ToImmutable()));
+                    new SuggestedActionSet(nestedSuggestedActions.ToImmutableAndFree()));
 
                 return Task.FromResult(_actionSets);
             }

src/EditorFeatures/Core/Implementation/TodoComment/AbstractTodoCommentIncrementalAnalyzer.cs

@@ -95,7 +95,7 @@ public async Task AnalyzeSyntaxAsync(Document document, InvocationReasons reason
 
         private async Task<ImmutableArray<TodoItem>> CreateItemsAsync(Document document, IList<TodoComment> comments, CancellationToken cancellationToken)
         {
-            var items = ImmutableArray.CreateBuilder<TodoItem>();
+            var items = ArrayBuilder<TodoItem>.GetInstance();
             if (comments != null)
             {
                 var text = await document.GetTextAsync(cancellationToken).ConfigureAwait(false);
@@ -107,7 +107,7 @@ private async Task<ImmutableArray<TodoItem>> CreateItemsAsync(Document document,
                 }
             }
 
-            return items.ToImmutable();
+            return items.ToImmutableAndFree();
         }
 
         private TodoItem CreateItem(Document document, SourceText text, SyntaxTree tree, TodoComment comment)

src/EditorFeatures/Test/Structure/AbstractSyntaxNodeStructureProviderTests.cs

@@ -37,7 +37,7 @@ internal sealed override async Task<BlockSpan[]> GetBlockSpansAsync(Document doc
             }
 
             var outliner = CreateProvider();
-            var actualRegions = ImmutableArray.CreateBuilder<BlockSpan>();
+            var actualRegions = ArrayBuilder<BlockSpan>.GetInstance();
             outliner.CollectBlockSpans(document, node, actualRegions, CancellationToken.None);
 
             // TODO: Determine why we get null outlining spans.

src/EditorFeatures/Test/Structure/AbstractSyntaxTriviaStructureProviderTests.cs

@@ -19,7 +19,7 @@ internal sealed override async Task<BlockSpan[]> GetBlockSpansAsync(Document doc
             var trivia = root.FindTrivia(position, findInsideTrivia: true);
 
             var outliner = CreateProvider();
-            var actualRegions = ImmutableArray.CreateBuilder<BlockSpan>();
+            var actualRegions = ArrayBuilder<BlockSpan>.GetInstance();
             outliner.CollectBlockSpans(document, trivia, actualRegions, CancellationToken.None);
 
             // TODO: Determine why we get null outlining spans.

src/Features/CSharp/Portable/Structure/CSharpStructureHelpers.cs

@@ -151,13 +151,13 @@ private static string GetCommentBannerText(SyntaxTrivia comment)
         internal static ImmutableArray<BlockSpan> CreateCommentBlockSpan(
             SyntaxTriviaList triviaList)
         {
-            var result = ImmutableArray.CreateBuilder<BlockSpan>();
+            var result = ArrayBuilder<BlockSpan>.GetInstance();
             CollectCommentBlockSpans(triviaList, result);
-            return result.ToImmutable();
+            return result.ToImmutableAndFree();
         }
 
         public static void CollectCommentBlockSpans(
-            SyntaxTriviaList triviaList, ImmutableArray<BlockSpan>.Builder spans)
+            SyntaxTriviaList triviaList, ArrayBuilder<BlockSpan> spans)
         {
             if (triviaList.Count > 0)
             {
@@ -205,7 +205,7 @@ private static string GetCommentBannerText(SyntaxTrivia comment)
         }
 
         public static void CollectCommentBlockSpans(
-            SyntaxNode node, ImmutableArray<BlockSpan>.Builder spans)
+            SyntaxNode node, ArrayBuilder<BlockSpan> spans)
         {
             if (node == null)
             {

src/Features/CSharp/Portable/Structure/Providers/AccessorDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class AccessorDeclarationStructureProvider : AbstractSyntaxNodeStructur
     {
         protected override void CollectBlockSpans(
             AccessorDeclarationSyntax accessorDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(accessorDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/AnonymousMethodExpressionStructureProvider.cs

@@ -11,7 +11,7 @@ internal class AnonymousMethodExpressionStructureProvider : AbstractSyntaxNodeSt
     {
         protected override void CollectBlockSpans(
             AnonymousMethodExpressionSyntax anonymousMethod,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             // fault tolerance

src/Features/CSharp/Portable/Structure/Providers/CompilationUnitStructureProvider.cs

@@ -12,7 +12,7 @@ internal class CompilationUnitStructureProvider : AbstractSyntaxNodeStructurePro
     {
         protected override void CollectBlockSpans(
             CompilationUnitSyntax compilationUnit,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(compilationUnit, spans);

src/Features/CSharp/Portable/Structure/Providers/ConstructorDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class ConstructorDeclarationStructureProvider : AbstractSyntaxNodeStruc
     {
         protected override void CollectBlockSpans(
             ConstructorDeclarationSyntax constructorDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(constructorDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/ConversionOperatorDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class ConversionOperatorDeclarationStructureProvider : AbstractSyntaxNo
     {
         protected override void CollectBlockSpans(
             ConversionOperatorDeclarationSyntax operatorDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(operatorDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/DelegateDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class DelegateDeclarationStructureProvider : AbstractSyntaxNodeStructur
     {
         protected override void CollectBlockSpans(
             DelegateDeclarationSyntax delegateDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(delegateDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/DestructorDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class DestructorDeclarationStructureProvider : AbstractSyntaxNodeStruct
     {
         protected override void CollectBlockSpans(
             DestructorDeclarationSyntax destructorDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(destructorDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/DisabledTextTriviaStructureProvider.cs

@@ -12,13 +12,15 @@ internal class DisabledTextTriviaStructureProvider : AbstractSyntaxTriviaStructu
         public override void CollectBlockSpans(
             Document document,
             SyntaxTrivia trivia,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CollectBlockSpans(trivia.SyntaxTree, trivia, spans, cancellationToken);
         }
 
-        public void CollectBlockSpans(SyntaxTree syntaxTree, SyntaxTrivia trivia, ImmutableArray<BlockSpan>.Builder spans, CancellationToken cancellationToken)
+        public void CollectBlockSpans(
+            SyntaxTree syntaxTree, SyntaxTrivia trivia,
+            ArrayBuilder<BlockSpan> spans, CancellationToken cancellationToken)
         {
             // We'll always be leading trivia of some token.
             var startPos = trivia.FullSpan.Start;

src/Features/CSharp/Portable/Structure/Providers/DocumentationCommentStructureProvider.cs

@@ -107,7 +107,7 @@ private static void AppendTextTokens(StringBuilder sb, SyntaxTokenList textToken
 
         protected override void CollectBlockSpans(
             DocumentationCommentTriviaSyntax documentationComment,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             var startPos = documentationComment.FullSpan.Start;

src/Features/CSharp/Portable/Structure/Providers/EnumDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class EnumDeclarationStructureProvider : AbstractSyntaxNodeStructurePro
     {
         protected override void CollectBlockSpans(
             EnumDeclarationSyntax enumDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(enumDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/EventDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class EventDeclarationStructureProvider : AbstractSyntaxNodeStructurePr
     {
         protected override void CollectBlockSpans(
             EventDeclarationSyntax eventDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(eventDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/EventFieldDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class EventFieldDeclarationStructureProvider : AbstractSyntaxNodeStruct
     {
         protected override void CollectBlockSpans(
             EventFieldDeclarationSyntax eventFieldDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(eventFieldDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/FieldDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class FieldDeclarationStructureProvider : AbstractSyntaxNodeStructurePr
     {
         protected override void CollectBlockSpans(
             FieldDeclarationSyntax fieldDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(fieldDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/IndexerDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class IndexerDeclarationStructureProvider : AbstractSyntaxNodeStructure
     {
         protected override void CollectBlockSpans(
             IndexerDeclarationSyntax indexerDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(indexerDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/MetadataAsSource/AbstractMetadataAsSourceStructureProvider.cs

@@ -12,7 +12,7 @@ internal abstract class AbstractMetadataAsSourceStructureProvider<TSyntaxNode> :
         where TSyntaxNode : SyntaxNode
     {
         protected override void CollectBlockSpans(
-            TSyntaxNode node, ImmutableArray<BlockSpan>.Builder spans, CancellationToken cancellationToken)
+            TSyntaxNode node, ArrayBuilder<BlockSpan> spans, CancellationToken cancellationToken)
         {
             var startToken = node.GetFirstToken();
             var endToken = GetEndToken(node);

src/Features/CSharp/Portable/Structure/Providers/MetadataAsSource/RegionDirectiveStructureProvider.cs

@@ -29,7 +29,7 @@ private static string GetBannerText(DirectiveTriviaSyntax simpleDirective)
 
         protected override void CollectBlockSpans(
             RegionDirectiveTriviaSyntax regionDirective,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             var match = regionDirective.GetMatchingDirective(cancellationToken);

src/Features/CSharp/Portable/Structure/Providers/MethodDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class MethodDeclarationStructureProvider : AbstractSyntaxNodeStructureP
     {
         protected override void CollectBlockSpans(
             MethodDeclarationSyntax methodDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(methodDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/NamespaceDeclarationStructureProvider.cs

@@ -12,7 +12,7 @@ internal class NamespaceDeclarationStructureProvider : AbstractSyntaxNodeStructu
     {
         protected override void CollectBlockSpans(
             NamespaceDeclarationSyntax namespaceDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             // add leading comments
@@ -47,7 +47,8 @@ internal class NamespaceDeclarationStructureProvider : AbstractSyntaxNodeStructu
             // finally, add any leading comments before the end of the namespace block
             if (!namespaceDeclaration.CloseBraceToken.IsMissing)
             {
-                CSharpStructureHelpers.CollectCommentBlockSpans(namespaceDeclaration.CloseBraceToken.LeadingTrivia, spans);
+                CSharpStructureHelpers.CollectCommentBlockSpans(
+                    namespaceDeclaration.CloseBraceToken.LeadingTrivia, spans);
             }
         }
 

src/Features/CSharp/Portable/Structure/Providers/OperatorDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class OperatorDeclarationStructureProvider : AbstractSyntaxNodeStructur
     {
         protected override void CollectBlockSpans(
             OperatorDeclarationSyntax operatorDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(operatorDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/ParenthesizedLambdaExpressionStructureProvider.cs

@@ -11,7 +11,7 @@ internal class ParenthesizedLambdaExpressionStructureProvider : AbstractSyntaxNo
     {
         protected override void CollectBlockSpans(
             ParenthesizedLambdaExpressionSyntax lambdaExpression,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             // fault tolerance

src/Features/CSharp/Portable/Structure/Providers/PropertyDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class PropertyDeclarationStructureProvider : AbstractSyntaxNodeStructur
     {
         protected override void CollectBlockSpans(
             PropertyDeclarationSyntax propertyDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(propertyDeclaration, spans);

src/Features/CSharp/Portable/Structure/Providers/RegionDirectiveStructureProvider.cs

@@ -29,7 +29,7 @@ private static string GetBannerText(DirectiveTriviaSyntax simpleDirective)
 
         protected override void CollectBlockSpans(
             RegionDirectiveTriviaSyntax regionDirective,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             var match = regionDirective.GetMatchingDirective(cancellationToken);

src/Features/CSharp/Portable/Structure/Providers/SimpleLambdaExpressionStructureProvider.cs

@@ -11,7 +11,7 @@ internal class SimpleLambdaExpressionStructureProvider : AbstractSyntaxNodeStruc
     {
         protected override void CollectBlockSpans(
             SimpleLambdaExpressionSyntax lambdaExpression,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             // fault tolerance

src/Features/CSharp/Portable/Structure/Providers/TypeDeclarationStructureProvider.cs

@@ -11,7 +11,7 @@ internal class TypeDeclarationStructureProvider : AbstractSyntaxNodeStructurePro
     {
         protected override void CollectBlockSpans(
             TypeDeclarationSyntax typeDeclaration,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             CSharpStructureHelpers.CollectCommentBlockSpans(typeDeclaration, spans);

src/Features/Core/Portable/CodeFixes/Suppression/AbstractSuppressionCodeFixProvider.GlobalSuppressMessageFixAllCodeAction.cs

@@ -189,7 +189,7 @@ private static void AddDiagnosticForSymbolIfNeeded(ISymbol targetSymbol, Diagnos
             private static ImmutableArray<Diagnostic> GetUniqueDiagnostics(List<Diagnostic> diagnostics)
             {
                 var uniqueIds = new HashSet<string>();
-                var uniqueDiagnostics = ImmutableArray.CreateBuilder<Diagnostic>();
+                var uniqueDiagnostics = ArrayBuilder<Diagnostic>.GetInstance();
                 foreach (var diagnostic in diagnostics)
                 {
                     if (uniqueIds.Add(diagnostic.Id))
@@ -198,7 +198,7 @@ private static ImmutableArray<Diagnostic> GetUniqueDiagnostics(List<Diagnostic>
                     }
                 }
 
-                return uniqueDiagnostics.ToImmutable();
+                return uniqueDiagnostics.ToImmutableAndFree();
             }
         }
     }

src/Features/Core/Portable/CodeFixes/Suppression/AbstractSuppressionCodeFixProvider.PragmaWarningBatchFixAllProvider.cs

@@ -28,8 +28,8 @@ public PragmaWarningBatchFixAllProvider(AbstractSuppressionCodeFixProvider suppr
                 Document document, ImmutableArray<Diagnostic> diagnostics, Action<CodeAction> addFix,
                 FixAllState fixAllState, CancellationToken cancellationToken)
             {
-                var pragmaActionsBuilder = ImmutableArray.CreateBuilder<IPragmaBasedCodeAction>();
-                var pragmaDiagnosticsBuilder = ImmutableArray.CreateBuilder<Diagnostic>();
+                var pragmaActionsBuilder = ArrayBuilder<IPragmaBasedCodeAction>.GetInstance();
+                var pragmaDiagnosticsBuilder = ArrayBuilder<Diagnostic>.GetInstance();
 
                 foreach (var diagnostic in diagnostics.Where(d => d.Location.IsInSource && !d.IsSuppressed))
                 {
@@ -54,7 +54,8 @@ public PragmaWarningBatchFixAllProvider(AbstractSuppressionCodeFixProvider suppr
                 {
                     var pragmaBatchFix = PragmaBatchFixHelpers.CreateBatchPragmaFix(
                         _suppressionFixProvider, document,
-                        pragmaActionsBuilder.ToImmutable(), pragmaDiagnosticsBuilder.ToImmutable(), 
+                        pragmaActionsBuilder.ToImmutableAndFree(), 
+                        pragmaDiagnosticsBuilder.ToImmutableAndFree(), 
                         fixAllState, cancellationToken);
 
                     addFix(pragmaBatchFix);

src/Features/Core/Portable/CodeFixes/Suppression/AbstractSuppressionCodeFixProvider.RemoveSuppressionCodeAction.BatchFixer.cs

@@ -37,8 +37,9 @@ public BatchFixer(AbstractSuppressionCodeFixProvider suppressionFixProvider)
                     FixAllState fixAllState, CancellationToken cancellationToken)
                 {
                     // Batch all the pragma remove suppression fixes by executing them sequentially for the document.
-                    var pragmaActionsBuilder = ImmutableArray.CreateBuilder<IPragmaBasedCodeAction>();
-                    var pragmaDiagnosticsBuilder = ImmutableArray.CreateBuilder<Diagnostic>();
+                    var pragmaActionsBuilder = ArrayBuilder<IPragmaBasedCodeAction>.GetInstance();
+                    var pragmaDiagnosticsBuilder = ArrayBuilder<Diagnostic>.GetInstance();
+
                     foreach (var diagnostic in diagnostics.Where(d => d.Location.IsInSource && d.IsSuppressed))
                     {
                         var span = diagnostic.Location.SourceSpan;
@@ -74,7 +75,8 @@ public BatchFixer(AbstractSuppressionCodeFixProvider suppressionFixProvider)
                     {
                         var pragmaBatchFix = PragmaBatchFixHelpers.CreateBatchPragmaFix(
                             _suppressionFixProvider, document,
-                            pragmaActionsBuilder.ToImmutable(), pragmaDiagnosticsBuilder.ToImmutable(),
+                            pragmaActionsBuilder.ToImmutableAndFree(),
+                            pragmaDiagnosticsBuilder.ToImmutableAndFree(),
                             fixAllState, cancellationToken);
 
                         addFix(pragmaBatchFix);
@@ -158,14 +160,14 @@ public BatchFixer(AbstractSuppressionCodeFixProvider suppressionFixProvider)
 
                 private static async Task<ImmutableArray<SyntaxNode>> GetAttributeNodesToFixAsync(ImmutableArray<AttributeRemoveAction> attributeRemoveFixes, CancellationToken cancellationToken)
                 {
-                    var builder = ImmutableArray.CreateBuilder<SyntaxNode>(attributeRemoveFixes.Length);
+                    var builder = ArrayBuilder<SyntaxNode>.GetInstance(attributeRemoveFixes.Length);
                     foreach (var attributeRemoveFix in attributeRemoveFixes)
                     {
                         var attributeToRemove = await attributeRemoveFix.GetAttributeToRemoveAsync(cancellationToken).ConfigureAwait(false);
                         builder.Add(attributeToRemove);
                     }
 
-                    return builder.ToImmutable();
+                    return builder.ToImmutableAndFree();
                 }
             }
         }

src/Features/Core/Portable/CodeRefactorings/ConvertToInterpolatedString/AbstractConvertToInterpolatedStringRefactoringProvider.cs

@@ -150,7 +150,7 @@ public override async Task ComputeRefactoringsAsync(CodeRefactoringContext conte
             SyntaxGenerator syntaxGenerator,
             ISyntaxFactsService syntaxFactsService)
         {
-            var builder = ImmutableArray.CreateBuilder<TExpressionSyntax>();
+            var builder = ArrayBuilder<TExpressionSyntax>.GetInstance();
             for (int i = 1; i < arguments.Count; i++)
             {
                 var argumentExpression = syntaxFactsService.GetExpressionOfArgument(arguments[i]);
@@ -166,7 +166,7 @@ public override async Task ComputeRefactoringsAsync(CodeRefactoringContext conte
                 }
             }
 
-            var expandedArguments = builder.ToImmutable();
+            var expandedArguments = builder.ToImmutableAndFree();
             return expandedArguments;
         }
 

src/Features/Core/Portable/Completion/CompletionService.cs

@@ -142,7 +142,7 @@ public virtual TextSpan GetDefaultCompletionListSpan(SourceText text, int caretP
         {
             var helper = CompletionHelper.GetHelper(document);
 
-            var bestItems = ImmutableArray.CreateBuilder<CompletionItem>();
+            var bestItems = ArrayBuilder<CompletionItem>.GetInstance();
             foreach (var item in items)
             {
                 if (bestItems.Count == 0)
@@ -171,7 +171,7 @@ public virtual TextSpan GetDefaultCompletionListSpan(SourceText text, int caretP
                 }
             }
 
-            return bestItems.ToImmutable();
+            return bestItems.ToImmutableAndFree();
         }
     }
 }
\ No newline at end of file

src/Features/Core/Portable/FindReferences/IDefinitionsAndReferencesFactory.cs

@@ -28,8 +28,8 @@ internal class DefaultDefinitionsAndReferencesFactory : IDefinitionsAndReference
         public DefinitionsAndReferences CreateDefinitionsAndReferences(
             Solution solution, IEnumerable<ReferencedSymbol> referencedSymbols)
         {
-            var definitions = ImmutableArray.CreateBuilder<DefinitionItem>();
-            var references = ImmutableArray.CreateBuilder<SourceReferenceItem>();
+            var definitions = ArrayBuilder<DefinitionItem>.GetInstance();
+            var references = ArrayBuilder<SourceReferenceItem>.GetInstance();
 
             var uniqueLocations = new HashSet<DocumentSpan>();
 
@@ -42,7 +42,8 @@ internal class DefaultDefinitionsAndReferencesFactory : IDefinitionsAndReference
                     solution, referencedSymbol, definitions, references, uniqueLocations);
             }
 
-            return new DefinitionsAndReferences(definitions.ToImmutable(), references.ToImmutable());
+            return new DefinitionsAndReferences(
+                definitions.ToImmutableAndFree(), references.ToImmutableAndFree());
         }
 
         /// <summary>
@@ -83,8 +84,8 @@ private static int GetPrecedence(ReferencedSymbol referencedSymbol)
         private void ProcessReferencedSymbol(
             Solution solution,
             ReferencedSymbol referencedSymbol,
-            ImmutableArray<DefinitionItem>.Builder definitions,
-            ImmutableArray<SourceReferenceItem>.Builder references,
+            ArrayBuilder<DefinitionItem> definitions,
+            ArrayBuilder<SourceReferenceItem> references,
             HashSet<DocumentSpan> uniqueSpans)
         {
             // See if this is a symbol we even want to present to the user.  If not,
@@ -122,7 +123,7 @@ private static int GetPrecedence(ReferencedSymbol referencedSymbol)
 
         private static void CreateReferences(
             ReferencedSymbol referencedSymbol,
-            ImmutableArray<SourceReferenceItem>.Builder references,
+            ArrayBuilder<SourceReferenceItem> references,
             DefinitionItem definitionItem,
             HashSet<DocumentSpan> uniqueSpans)
         {
@@ -155,7 +156,7 @@ internal static class DefinitionItemExtensions
             var displayIfNoReferences = definition.ShouldShowWithNoReferenceLocations(
                 showMetadataSymbolsWithoutReferences: false);
 
-            var sourceLocations = ImmutableArray.CreateBuilder<DocumentSpan>();
+            var sourceLocations = ArrayBuilder<DocumentSpan>.GetInstance();
 
             // If it's a namespace, don't create any normal lcoation.  Namespaces
             // come from many different sources, but we'll only show a single 
@@ -203,7 +204,7 @@ internal static class DefinitionItemExtensions
             }
 
             return DefinitionItem.Create(
-                tags, displayParts, sourceLocations.ToImmutable(), displayIfNoReferences);
+                tags, displayParts, sourceLocations.ToImmutableAndFree(), displayIfNoReferences);
         }
 
         public static SourceReferenceItem TryCreateSourceReferenceItem(

src/Features/Core/Portable/MetadataAsSource/AbstractMetadataAsSourceService.DocCommentFormatter.cs

@@ -24,7 +24,7 @@ internal class DocCommentFormatter
 
             internal static ImmutableArray<string> Format(IDocumentationCommentFormattingService docCommentFormattingService, DocumentationComment docComment)
             {
-                var formattedCommentLinesBuilder = ImmutableArray.CreateBuilder<string>();
+                var formattedCommentLinesBuilder = ArrayBuilder<string>.GetInstance();
                 var lineBuilder = new StringBuilder();
 
                 var formattedSummaryText = docCommentFormattingService.Format(docComment.SummaryText);
@@ -149,12 +149,12 @@ internal static ImmutableArray<string> Format(IDocumentationCommentFormattingSer
                     formattedCommentLinesBuilder.RemoveAt(formattedCommentLinesBuilder.Count - 1);
                 }
 
-                return formattedCommentLinesBuilder.ToImmutable();
+                return formattedCommentLinesBuilder.ToImmutableAndFree();
             }
 
             private static ImmutableArray<string> CreateWrappedTextFromRawText(string rawText)
             {
-                var lines = ImmutableArray.CreateBuilder<string>();
+                var lines = ArrayBuilder<string>.GetInstance();
 
                 // First split the string into constituent lines.
                 var split = rawText.Split(new[] { "\r\n" }, System.StringSplitOptions.None);
@@ -165,10 +165,11 @@ private static ImmutableArray<string> CreateWrappedTextFromRawText(string rawTex
                     SplitRawLineIntoFormattedLines(item, lines);
                 }
 
-                return lines.ToImmutable();
+                return lines.ToImmutableAndFree();
             }
 
-            private static void SplitRawLineIntoFormattedLines(string line, ImmutableArray<string>.Builder lines)
+            private static void SplitRawLineIntoFormattedLines(
+                string line, ArrayBuilder<string> lines)
             {
                 var indent = new StringBuilder().Append(' ', s_indentSize * 2).ToString();
 

src/Features/Core/Portable/Structure/Syntax/AbstractBlockStructureProvider.cs

@@ -45,7 +45,7 @@ public override void ProvideBlockStructure(BlockStructureContext context)
         private void ProvideBlockStructureWorker(
             BlockStructureContext context, SyntaxNode syntaxRoot)
         {
-            var spans = ImmutableArray.CreateBuilder<BlockSpan>();
+            var spans = ArrayBuilder<BlockSpan>.GetInstance();
             BlockSpanCollector.CollectBlockSpans(
                 context.Document, syntaxRoot, _nodeProviderMap, _triviaProviderMap, spans, context.CancellationToken);
 
@@ -53,6 +53,8 @@ public override void ProvideBlockStructure(BlockStructureContext context)
             {
                 context.AddBlockSpan(region);
             }
+
+            spans.Free();
         }
 
         /// <summary>

src/Features/Core/Portable/Structure/Syntax/AbstractSyntaxNodeStructureProvider.cs

@@ -12,7 +12,7 @@ internal abstract class AbstractSyntaxNodeStructureProvider<TSyntaxNode> : Abstr
         public override void CollectBlockSpans(
             Document document,
             SyntaxNode node,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             if (!SupportedInWorkspaceKind(document.Project.Solution.Workspace.Kind))
@@ -26,15 +26,15 @@ internal abstract class AbstractSyntaxNodeStructureProvider<TSyntaxNode> : Abstr
         public sealed override void CollectBlockSpans(
             Document document,
             SyntaxTrivia trivia,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             throw new NotSupportedException();
         }
 
         private void CollectBlockSpans(
-            SyntaxNode node, 
-            ImmutableArray<BlockSpan>.Builder spans,
+            SyntaxNode node,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             if (node is TSyntaxNode)
@@ -50,6 +50,6 @@ protected virtual bool SupportedInWorkspaceKind(string kind)
         }
 
         protected abstract void CollectBlockSpans(
-            TSyntaxNode node, ImmutableArray<BlockSpan>.Builder spans, CancellationToken cancellationToken);
+            TSyntaxNode node, ArrayBuilder<BlockSpan> spans, CancellationToken cancellationToken);
     }
 }
\ No newline at end of file

src/Features/Core/Portable/Structure/Syntax/AbstractSyntaxStructureProvider.cs

@@ -10,13 +10,13 @@ internal abstract class AbstractSyntaxStructureProvider
         public abstract void CollectBlockSpans(
             Document document,
             SyntaxNode node,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken);
 
         public abstract void CollectBlockSpans(
             Document document,
             SyntaxTrivia trivia,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken);
     }
 }
\ No newline at end of file

src/Features/Core/Portable/Structure/Syntax/AbstractSyntaxTriviaStructureProvider.cs

@@ -11,7 +11,7 @@ internal abstract class AbstractSyntaxTriviaStructureProvider : AbstractSyntaxSt
         public sealed override void CollectBlockSpans(
             Document document,
             SyntaxNode node,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             throw new NotSupportedException();

src/Features/Core/Portable/Structure/Syntax/BlockSpanCollector.cs

@@ -11,14 +11,14 @@ internal class BlockSpanCollector
         private readonly Document _document;
         private readonly ImmutableDictionary<Type, ImmutableArray<AbstractSyntaxStructureProvider>> _nodeProviderMap;
         private readonly ImmutableDictionary<int, ImmutableArray<AbstractSyntaxStructureProvider>> _triviaProviderMap;
-        private readonly ImmutableArray<BlockSpan>.Builder _spans;
+        private readonly ArrayBuilder<BlockSpan> _spans;
         private readonly CancellationToken _cancellationToken;
 
         private BlockSpanCollector(
             Document document,
             ImmutableDictionary<Type, ImmutableArray<AbstractSyntaxStructureProvider>> nodeOutlinerMap,
             ImmutableDictionary<int, ImmutableArray<AbstractSyntaxStructureProvider>> triviaOutlinerMap,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             _document = document;
@@ -33,7 +33,7 @@ internal class BlockSpanCollector
             SyntaxNode syntaxRoot,
             ImmutableDictionary<Type, ImmutableArray<AbstractSyntaxStructureProvider>> nodeOutlinerMap,
             ImmutableDictionary<int, ImmutableArray<AbstractSyntaxStructureProvider>> triviaOutlinerMap,
-            ImmutableArray<BlockSpan>.Builder spans,
+            ArrayBuilder<BlockSpan> spans,
             CancellationToken cancellationToken)
         {
             var collector = new BlockSpanCollector(document, nodeOutlinerMap, triviaOutlinerMap, spans, cancellationToken);

src/Features/VisualBasic/Portable/Structure/Providers/AccessorDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of AccessorStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(accessorDeclaration As AccessorStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(accessorDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/CompilationUnitStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of CompilationUnitSyntax)
 
         Protected Overrides Sub CollectBlockSpans(compilationUnit As CompilationUnitSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             Dim regions As New List(Of BlockSpan)
 

src/Features/VisualBasic/Portable/Structure/Providers/ConstructorDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of SubNewStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(constructorDeclaration As SubNewStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             Dim regions As New List(Of BlockSpan)
 

src/Features/VisualBasic/Portable/Structure/Providers/DelegateDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of DelegateStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(delegateDeclaration As DelegateStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(delegateDeclaration, spans)
         End Sub

src/Features/VisualBasic/Portable/Structure/Providers/DisabledTextTriviaStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxTriviaStructureProvider
 
         Public Overrides Sub CollectBlockSpans(document As Document, trivia As SyntaxTrivia,
-                                               spans As ImmutableArray(Of BlockSpan).Builder,
+                                               spans As ArrayBuilder(Of BlockSpan),
                                                cancellationToken As CancellationToken)
             If trivia.Kind = SyntaxKind.DisabledTextTrivia Then
                 ' Don't include trailing line breaks in spanToCollapse

src/Features/VisualBasic/Portable/Structure/Providers/DocumentationCommentStructureProvider.vb

@@ -71,7 +71,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         End Sub
 
         Protected Overrides Sub CollectBlockSpans(documentationComment As DocumentationCommentTriviaSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             Dim firstCommentToken = documentationComment.ChildNodesAndTokens().FirstOrNullable()
             Dim lastCommentToken = documentationComment.ChildNodesAndTokens().LastOrNullable()

src/Features/VisualBasic/Portable/Structure/Providers/EnumDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of EnumStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(enumDeclaration As EnumStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(enumDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/EventDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of EventStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(eventDeclaration As EventStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(eventDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/ExternalMethodDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of DeclareStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(externalMethodDeclaration As DeclareStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(externalMethodDeclaration, spans)
         End Sub

src/Features/VisualBasic/Portable/Structure/Providers/FieldDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of FieldDeclarationSyntax)
 
         Protected Overrides Sub CollectBlockSpans(fieldDeclaration As FieldDeclarationSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(fieldDeclaration, spans)
         End Sub

src/Features/VisualBasic/Portable/Structure/Providers/MetadataAsSource/AbstractMetadataAsSourceStructureProvider.vb

@@ -11,8 +11,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure.MetadataAsSource
         Inherits AbstractSyntaxNodeStructureProvider(Of TSyntaxNode)
 
         Protected Overrides Sub CollectBlockSpans(node As TSyntaxNode,
-                                                      spans As ImmutableArray(Of BlockSpan).Builder,
-                                                      cancellationToken As CancellationToken)
+                                                  spans As ArrayBuilder(Of BlockSpan),
+                                                  cancellationToken As CancellationToken)
             Dim startToken = node.GetFirstToken()
             Dim endToken = GetEndToken(node)
 

src/Features/VisualBasic/Portable/Structure/Providers/MetadataAsSource/MetadataRegionDirectiveStructureProvider.vb

@@ -21,7 +21,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure.MetadataAsSource
         End Function
 
         Protected Overrides Sub CollectBlockSpans(regionDirective As RegionDirectiveTriviaSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             Dim match = regionDirective.GetMatchingStartOrEndDirective(cancellationToken)
             If match IsNot Nothing Then

src/Features/VisualBasic/Portable/Structure/Providers/MethodDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of MethodStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(methodDeclaration As MethodStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(methodDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/MultilineLambdaStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of MultiLineLambdaExpressionSyntax)
 
         Protected Overrides Sub CollectBlockSpans(lambdaExpression As MultiLineLambdaExpressionSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             If Not lambdaExpression.EndSubOrFunctionStatement.IsMissing Then
                 spans.Add(CreateRegionFromBlock(

src/Features/VisualBasic/Portable/Structure/Providers/NamespaceDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of NamespaceStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(namespaceDeclaration As NamespaceStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(namespaceDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/OperatorDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of OperatorStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(operatorDeclaration As OperatorStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(operatorDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/PropertyDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of PropertyStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(propertyDeclaration As PropertyStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(propertyDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/RegionDirectiveStructureProvider.vb

@@ -21,7 +21,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         End Function
 
         Protected Overrides Sub CollectBlockSpans(regionDirective As RegionDirectiveTriviaSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             Dim matchingDirective = regionDirective.GetMatchingStartOrEndDirective(cancellationToken)
             If matchingDirective IsNot Nothing Then

src/Features/VisualBasic/Portable/Structure/Providers/TypeDeclarationStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of TypeStatementSyntax)
 
         Protected Overrides Sub CollectBlockSpans(typeDeclaration As TypeStatementSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             CollectCommentsRegions(typeDeclaration, spans)
 

src/Features/VisualBasic/Portable/Structure/Providers/XmlExpressionStructureProvider.vb

@@ -10,7 +10,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         Inherits AbstractSyntaxNodeStructureProvider(Of XmlNodeSyntax)
 
         Protected Overrides Sub CollectBlockSpans(xmlExpression As XmlNodeSyntax,
-                                                  spans As ImmutableArray(Of BlockSpan).Builder,
+                                                  spans As ArrayBuilder(Of BlockSpan),
                                                   cancellationToken As CancellationToken)
             ' If this XML expression is inside structured trivia (i.e. an XML doc comment), don't outline.
             If xmlExpression.HasAncestor(Of DocumentationCommentTriviaSyntax)() Then

src/Features/VisualBasic/Portable/Structure/VisualBasicStructureHelpers.vb

@@ -29,12 +29,13 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
 
         ' For testing purposes
         Friend Function CreateCommentsRegions(triviaList As SyntaxTriviaList) As ImmutableArray(Of BlockSpan)
-            Dim spans = ImmutableArray.CreateBuilder(Of BlockSpan)
+            Dim spans = ArrayBuilder(Of BlockSpan).GetInstance()
             CollectCommentsRegions(triviaList, spans)
-            Return spans.ToImmutable()
+            Return spans.ToImmutableAndFree()
         End Function
 
-        Friend Sub CollectCommentsRegions(triviaList As SyntaxTriviaList, spans As ImmutableArray(Of BlockSpan).Builder)
+        Friend Sub CollectCommentsRegions(triviaList As SyntaxTriviaList,
+                                          spans As ArrayBuilder(Of BlockSpan))
             If triviaList.Count > 0 Then
                 Dim startComment As SyntaxTrivia? = Nothing
                 Dim endComment As SyntaxTrivia? = Nothing
@@ -64,7 +65,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Structure
         End Sub
 
         Friend Sub CollectCommentsRegions(node As SyntaxNode,
-                                          spans As ImmutableArray(Of BlockSpan).Builder)
+                                          spans As ArrayBuilder(Of BlockSpan))
             If node Is Nothing Then
                 Throw New ArgumentNullException(NameOf(node))
             End If

src/Scripting/Core/ScriptState.cs

@@ -88,7 +88,7 @@ public ScriptVariable GetVariable(string name)
 
         private ImmutableArray<ScriptVariable> CreateVariables()
         {
-            var result = ImmutableArray.CreateBuilder<ScriptVariable>();
+            var result = ArrayBuilder<ScriptVariable>.GetInstance();
 
             var executionState = ExecutionState;
 
@@ -108,7 +108,7 @@ private ImmutableArray<ScriptVariable> CreateVariables()
                 }
             }
 
-            return result.ToImmutable();
+            return result.ToImmutableAndFree();
         }
 
         private IReadOnlyDictionary<string, int> GetVariableMap()

src/VisualStudio/Core/Def/Implementation/ProjectSystem/AbstractProject.cs

@@ -305,7 +305,7 @@ protected ImmutableArray<string> GetStrongNameKeyPaths()
                 return ImmutableArray<string>.Empty;
             }
 
-            var builder = ImmutableArray.CreateBuilder<string>();
+            var builder = ArrayBuilder<string>.GetInstance();
             if (this.ContainingDirectoryPathOpt != null)
             {
                 builder.Add(this.ContainingDirectoryPathOpt);
@@ -316,7 +316,7 @@ protected ImmutableArray<string> GetStrongNameKeyPaths()
                 builder.Add(Path.GetDirectoryName(outputPath));
             }
 
-            return builder.ToImmutable();
+            return builder.ToImmutableAndFree();
         }
 
         public ImmutableArray<ProjectReference> GetCurrentProjectReferences()

src/VisualStudio/Core/Def/Implementation/ProjectSystem/MetadataReferences/VisualStudioMetadataReferenceManager.RecoverableMetadataValueSource.cs

@@ -47,14 +47,14 @@ public override AssemblyMetadata GetValue(CancellationToken cancellationToken)
 
             private AssemblyMetadata RecoverMetadata()
             {
-                var moduleBuilder = ImmutableArray.CreateBuilder<ModuleMetadata>(_storages.Count);
+                var moduleBuilder = ArrayBuilder<ModuleMetadata>.GetInstance(_storages.Count);
 
                 foreach (var storage in _storages)
                 {
                     moduleBuilder.Add(GetModuleMetadata(storage));
                 }
 
-                var metadata = AssemblyMetadata.Create(moduleBuilder.ToImmutable());
+                var metadata = AssemblyMetadata.Create(moduleBuilder.ToImmutableAndFree());
                 _weakValue.SetTarget(metadata);
 
                 return metadata;

src/VisualStudio/Core/Def/Implementation/ProjectSystem/MetadataReferences/VisualStudioMetadataReferenceManager.cs

@@ -318,14 +318,13 @@ private bool TryGetFileMappingFromMetadataImporter(FileKey fileKey, out IMetaDat
             FileKey fileKey, ModuleMetadata manifestModule, List<ITemporaryStreamStorage> storages,
             Func<FileKey, List<ITemporaryStreamStorage>, ModuleMetadata> moduleMetadataFactory)
         {
-            ImmutableArray<ModuleMetadata>.Builder moduleBuilder = null;
+            var moduleBuilder = ArrayBuilder<ModuleMetadata>.GetInstance();
 
             string assemblyDir = null;
             foreach (string moduleName in manifestModule.GetModuleNames())
             {
-                if (moduleBuilder == null)
+                if (moduleBuilder.Count == 0)
                 {
-                    moduleBuilder = ImmutableArray.CreateBuilder<ModuleMetadata>();
                     moduleBuilder.Add(manifestModule);
                     assemblyDir = Path.GetDirectoryName(fileKey.FullPath);
                 }
@@ -336,8 +335,8 @@ private bool TryGetFileMappingFromMetadataImporter(FileKey fileKey, out IMetaDat
                 moduleBuilder.Add(metadata);
             }
 
-            var modules = (moduleBuilder != null) ? moduleBuilder.ToImmutable() : ImmutableArray.Create(manifestModule);
+            var modules = moduleBuilder.ToImmutableAndFree();
             return AssemblyMetadata.Create(modules);
         }
     }
-}
+}
\ No newline at end of file

src/VisualStudio/Core/Def/Implementation/TableDataSource/Extensions.cs

@@ -19,24 +19,24 @@ internal static class Extensions
     {
         public static ImmutableArray<TResult> ToImmutableArray<TSource, TResult>(this IList<TSource> list, Func<TSource, TResult> selector)
         {
-            var builder = ImmutableArray.CreateBuilder<TResult>(list.Count);
+            var builder = ArrayBuilder<TResult>.GetInstance(list.Count);
             for (var i = 0; i < list.Count; i++)
             {
                 builder.Add(selector(list[i]));
             }
 
-            return builder.ToImmutable();
+            return builder.ToImmutableAndFree();
         }
 
         public static ImmutableArray<TableItem<T>> MergeDuplicatesOrderedBy<T>(this IEnumerable<IList<TableItem<T>>> groupedItems, Func<IEnumerable<TableItem<T>>, IEnumerable<TableItem<T>>> orderer)
         {
-            var builder = ImmutableArray.CreateBuilder<TableItem<T>>();
+            var builder = ArrayBuilder<TableItem<T>>.GetInstance();
             foreach (var item in orderer(groupedItems.Select(g => g.Deduplicate())))
             {
                 builder.Add(item);
             }
 
-            return builder.ToImmutable();
+            return builder.ToImmutableAndFree();
         }
 
         private static TableItem<T> Deduplicate<T>(this IList<TableItem<T>> duplicatedItems)

src/VisualStudio/Core/Def/Implementation/TableDataSource/Suppression/VisualStudioDiagnosticListSuppressionStateService.cs

@@ -215,7 +215,8 @@ private static AbstractTableEntriesSnapshot<DiagnosticData> GetEntriesSnapshot(I
         /// </summary>
         public async Task<ImmutableArray<DiagnosticData>> GetSelectedItemsAsync(bool isAddSuppression, CancellationToken cancellationToken)
         {
-            var builder = ImmutableArray.CreateBuilder<DiagnosticData>();
+            var builder = ArrayBuilder<DiagnosticData>.GetInstance();
+
             Dictionary<string, Project> projectNameToProjectMapOpt = null;
             Dictionary<Project, ImmutableDictionary<string, Document>> filePathToDocumentMapOpt = null;
 
@@ -331,7 +332,7 @@ public async Task<ImmutableArray<DiagnosticData>> GetSelectedItemsAsync(bool isA
                 }
             }
 
-            return builder.ToImmutable();
+            return builder.ToImmutableAndFree();
         }
 
         private static async Task<ImmutableDictionary<string, Document>> GetFilePathToDocumentMapAsync(Project project, CancellationToken cancellationToken)

src/VisualStudio/Core/Def/Implementation/TableDataSource/Suppression/VisualStudioSuppressionFixService.cs

@@ -128,7 +128,8 @@ public bool RemoveSuppressions(bool selectedErrorListEntriesOnly, IVsHierarchy p
 
         private async Task<ImmutableArray<DiagnosticData>> GetAllBuildDiagnosticsAsync(Func<Project, bool> shouldFixInProject, CancellationToken cancellationToken)
         {
-            var builder = ImmutableArray.CreateBuilder<DiagnosticData>();
+            var builder = ArrayBuilder<DiagnosticData>.GetInstance();
+
             var buildDiagnostics = _buildErrorDiagnosticService.GetBuildErrors().Where(d => d.ProjectId != null && d.Severity != DiagnosticSeverity.Hidden);
             var solution = _workspace.CurrentSolution;
             foreach (var diagnosticsByProject in buildDiagnostics.GroupBy(d => d.ProjectId))
@@ -171,7 +172,7 @@ private async Task<ImmutableArray<DiagnosticData>> GetAllBuildDiagnosticsAsync(F
                 }
             }
 
-            return builder.ToImmutable();
+            return builder.ToImmutableAndFree();
         }
 
         private static string GetFixTitle(bool isAddSuppression)

src/VisualStudio/Core/Def/Implementation/Workspace/VisualStudioDocumentTrackingService.cs

@@ -72,13 +72,13 @@ public ImmutableArray<DocumentId> GetVisibleDocuments()
                 return ImmutableArray.Create<DocumentId>();
             }
 
-            ImmutableArray<DocumentId>.Builder ids = ImmutableArray.CreateBuilder<DocumentId>(snapshot.Count);
+            var ids = ArrayBuilder<DocumentId>.GetInstance(snapshot.Count);
             foreach (var frame in snapshot)
             {
                 ids.Add(frame.Id);
             }
 
-            return ids.ToImmutable();
+            return ids.ToImmutableAndFree();
         }
 
         /// <summary>

src/VisualStudio/Core/Impl/CodeModel/Collections/CodeElementSnapshot.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
 using Microsoft.VisualStudio;
 using Microsoft.VisualStudio.LanguageServices.Implementation.CodeModel.Interop;
 
@@ -14,7 +15,7 @@ internal class CodeElementSnapshot : Snapshot
         public CodeElementSnapshot(ICodeElements codeElements)
         {
             var count = codeElements.Count;
-            var elementsBuilder = ImmutableArray.CreateBuilder<EnvDTE.CodeElement>(count);
+            var elementsBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance(count);
 
             for (int i = 0; i < count; i++)
             {
@@ -26,7 +27,7 @@ public CodeElementSnapshot(ICodeElements codeElements)
                 }
             }
 
-            _elements = elementsBuilder.ToImmutable();
+            _elements = elementsBuilder.ToImmutableAndFree();
         }
 
         public CodeElementSnapshot(ImmutableArray<EnvDTE.CodeElement> elements)

src/VisualStudio/Core/Impl/CodeModel/Collections/ExternalMemberCollection.cs

@@ -51,7 +51,7 @@ private ImmutableArray<EnvDTE.CodeElement> GetChildren()
                     throw Exceptions.ThrowEFail();
                 }
 
-                var childrenBuilder = ImmutableArray.CreateBuilder<EnvDTE.CodeElement>();
+                var childrenBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance();
 
                 foreach (var member in typeSymbol.GetMembers())
                 {
@@ -66,7 +66,7 @@ private ImmutableArray<EnvDTE.CodeElement> GetChildren()
                     childrenBuilder.Add(this.State.CodeModelService.CreateExternalCodeElement(this.State, _projectId, typeMember));
                 }
 
-                _children = childrenBuilder.ToImmutable();
+                _children = childrenBuilder.ToImmutableAndFree();
             }
 
             return _children;

src/VisualStudio/Core/Impl/CodeModel/Collections/ExternalNamespaceCollection.cs

@@ -39,14 +39,14 @@ private ImmutableArray<EnvDTE.CodeElement> GetChildren()
         {
             if (_children == null)
             {
-                var childrenBuilder = ImmutableArray.CreateBuilder<EnvDTE.CodeElement>();
+                var childrenBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance();
 
                 foreach (var child in ExternalNamespaceEnumerator.ChildrenOfNamespace(this.State, _projectId, _namespaceSymbolId))
                 {
                     childrenBuilder.Add(child);
                 }
 
-                _children = childrenBuilder.ToImmutable();
+                _children = childrenBuilder.ToImmutableAndFree();
             }
 
             return _children;

src/VisualStudio/Core/Impl/CodeModel/Collections/ExternalOverloadsCollection.cs

@@ -51,7 +51,7 @@ private ImmutableArray<EnvDTE.CodeElement> EnumerateOverloads()
                 return ImmutableArray.Create((EnvDTE.CodeElement)Parent);
             }
 
-            var overloadsBuilder = ImmutableArray.CreateBuilder<EnvDTE.CodeElement>();
+            var overloadsBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance();
             foreach (var method in symbol.ContainingType.GetMembers(symbol.Name))
             {
                 if (method.Kind != SymbolKind.Method)
@@ -66,7 +66,7 @@ private ImmutableArray<EnvDTE.CodeElement> EnumerateOverloads()
                 }
             }
 
-            return overloadsBuilder.ToImmutable();
+            return overloadsBuilder.ToImmutableAndFree();
         }
 
         public override int Count

src/VisualStudio/Core/Impl/CodeModel/Collections/InheritsImplementsCollection.cs

@@ -56,11 +56,12 @@ internal override Snapshot CreateSnapshot()
             var node = LookupNode();
             var parentElement = (AbstractCodeElement)this.Parent;
 
-            var nodesBuilder = ImmutableArray.CreateBuilder<SyntaxNode>();
+            var nodesBuilder = ArrayBuilder<SyntaxNode>.GetInstance();
             nodesBuilder.AddRange(CodeModelService.GetInheritsNodes(node));
             nodesBuilder.AddRange(CodeModelService.GetImplementsNodes(node));
 
-            return new NodeSnapshot(this.State, _fileCodeModel, node, parentElement, nodesBuilder.ToImmutable());
+            return new NodeSnapshot(this.State, _fileCodeModel, node, parentElement,
+                nodesBuilder.ToImmutableAndFree());
         }
 
         protected override bool TryGetItemByIndex(int index, out EnvDTE.CodeElement element)

src/VisualStudio/Core/Impl/CodeModel/Collections/NamespaceCollection.cs

@@ -95,13 +95,14 @@ internal override Snapshot CreateSnapshot()
                 ? (AbstractCodeElement)this.Parent
                 : null;
 
-            var nodesBuilder = ImmutableArray.CreateBuilder<SyntaxNode>();
+            var nodesBuilder = ArrayBuilder<SyntaxNode>.GetInstance();
             nodesBuilder.AddRange(CodeModelService.GetOptionNodes(node));
             nodesBuilder.AddRange(CodeModelService.GetImportNodes(node));
             nodesBuilder.AddRange(CodeModelService.GetAttributeNodes(node));
             nodesBuilder.AddRange(CodeModelService.GetLogicalSupportedMemberNodes(node));
 
-            return new NodeSnapshot(this.State, _fileCodeModel, node, parentElement, nodesBuilder.ToImmutable());
+            return new NodeSnapshot(this.State, _fileCodeModel, node, parentElement, 
+                nodesBuilder.ToImmutableAndFree());
         }
 
         protected override bool TryGetItemByIndex(int index, out EnvDTE.CodeElement element)

src/VisualStudio/Core/Impl/CodeModel/Collections/OverloadsCollection.cs

@@ -55,7 +55,7 @@ private ImmutableArray<EnvDTE.CodeElement> GetOverloads()
 
                 var solution = this.Workspace.CurrentSolution;
 
-                var overloadsBuilder = ImmutableArray.CreateBuilder<EnvDTE.CodeElement>();
+                var overloadsBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance();
                 foreach (var method in symbol.ContainingType.GetMembers(symbol.Name))
                 {
                     if (method.Kind != SymbolKind.Method)
@@ -84,7 +84,7 @@ private ImmutableArray<EnvDTE.CodeElement> GetOverloads()
                     }
                 }
 
-                _overloads = overloadsBuilder.ToImmutable();
+                _overloads = overloadsBuilder.ToImmutableAndFree();
             }
 
             return _overloads;

src/VisualStudio/Core/Impl/CodeModel/Collections/PartialTypeCollection.cs

@@ -3,6 +3,7 @@
 using System.Collections.Immutable;
 using System.Linq;
 using System.Runtime.InteropServices;
+using Microsoft.CodeAnalysis;
 using Microsoft.VisualStudio.LanguageServices.Implementation.CodeModel.InternalElements;
 using Microsoft.VisualStudio.LanguageServices.Implementation.CodeModel.Interop;
 using Microsoft.VisualStudio.LanguageServices.Implementation.Interop;
@@ -43,7 +44,7 @@ private ImmutableArray<EnvDTE.CodeElement> GetParts()
             // property is accessed on CodeClass, CodeStruct or CodeInterface, consumers would hit this behavior rarely.
             if (_parts == null)
             {
-                var partsBuilder = ImmutableArray.CreateBuilder<EnvDTE.CodeElement>();
+                var partsBuilder = ArrayBuilder<EnvDTE.CodeElement>.GetInstance();
 
                 var solution = this.Workspace.CurrentSolution;
                 var symbol = ParentType.LookupSymbol();
@@ -67,7 +68,7 @@ private ImmutableArray<EnvDTE.CodeElement> GetParts()
                     }
                 }
 
-                _parts = partsBuilder.ToImmutable();
+                _parts = partsBuilder.ToImmutableAndFree();
             }
 
             return _parts;

src/VisualStudio/Core/Impl/CodeModel/Collections/TypeCollection.cs

@@ -57,10 +57,11 @@ internal override Snapshot CreateSnapshot()
             var node = LookupNode();
             var parentElement = (AbstractCodeElement)this.Parent;
 
-            var nodesBuilder = ImmutableArray.CreateBuilder<SyntaxNode>();
+            var nodesBuilder = ArrayBuilder<SyntaxNode>.GetInstance();
             nodesBuilder.AddRange(CodeModelService.GetLogicalSupportedMemberNodes(node));
 
-            return new NodeSnapshot(this.State, _fileCodeModel, node, parentElement, nodesBuilder.ToImmutable());
+            return new NodeSnapshot(this.State, _fileCodeModel, node, parentElement, 
+                nodesBuilder.ToImmutableAndFree());
         }
 
         protected override bool TryGetItemByIndex(int index, out EnvDTE.CodeElement element)

src/VisualStudio/Core/Impl/CodeModel/ExternalElements/AbstractExternalCodeType.cs

@@ -55,7 +55,7 @@ public EnvDTE.CodeElements Bases
         {
             get
             {
-                var builder = ImmutableArray.CreateBuilder<INamedTypeSymbol>();
+                var builder = ArrayBuilder<INamedTypeSymbol>.GetInstance();
 
                 var typeSymbol = TypeSymbol;
                 if (typeSymbol.TypeKind == TypeKind.Interface)
@@ -67,7 +67,8 @@ public EnvDTE.CodeElements Bases
                     builder.Add(typeSymbol.BaseType);
                 }
 
-                return ExternalTypeCollection.Create(this.State, this, this.ProjectId, builder.ToImmutable());
+                return ExternalTypeCollection.Create(this.State, this, this.ProjectId, 
+                    builder.ToImmutableAndFree());
             }
         }
 

src/VisualStudio/Core/Next/FindReferences/StreamingFindReferencesPresenter.TableDataSourceFindReferencesContext.cs

@@ -426,7 +426,7 @@ private void Order(List<ClassifiedSpan> syntaxSpans)
                 // Take all the syntax parts.  However, if any have been overridden by a 
                 // semantic part, then choose that one.
 
-                var finalParts = ImmutableArray.CreateBuilder<ClassifiedSpan>();
+                var finalParts = ArrayBuilder<ClassifiedSpan>.GetInstance();
                 var lastReplacementIndex = 0;
                 for (int i = 0, n = syntaxParts.Count; i < n; i++)
                 {
@@ -453,7 +453,7 @@ private void Order(List<ClassifiedSpan> syntaxSpans)
                     }
                 }
 
-                return finalParts.ToImmutable();
+                return finalParts.ToImmutableAndFree();
             }
 
             private bool IsClassifiedAsText(ClassifiedSpan partAndSpan)

src/VisualStudio/Core/SolutionExplorerShim/AnalyzerItem/AnalyzerItemSource.cs

@@ -201,7 +201,7 @@ private ImmutableArray<AnalyzerReference> GetFilteredAnalyzers(IEnumerable<Analy
             var analyzersWithLoadErrors = GetAnalyzersWithLoadErrors();
 
             // Filter out analyzer dependencies which have no diagnostic analyzers, but still retain the unresolved analyzers and analyzers with load errors.
-            var builder = ImmutableArray.CreateBuilder<AnalyzerReference>();
+            var builder = ArrayBuilder<AnalyzerReference>.GetInstance();
             foreach (var analyzerReference in analyzerReferences)
             {
                 // Analyzer dependency:
@@ -220,7 +220,7 @@ private ImmutableArray<AnalyzerReference> GetFilteredAnalyzers(IEnumerable<Analy
                 builder.Add(analyzerReference);
             }
 
-            return builder.ToImmutable();
+            return builder.ToImmutableAndFree();
         }
     }
 }

src/Workspaces/CSharp/Portable/LanguageServices/CSharpSyntaxFactsService.cs

@@ -907,7 +907,7 @@ private ImmutableArray<string> GetInheritanceNames(BaseListSyntax baseList)
                 return ImmutableArray<string>.Empty;
             }
 
-            var builder = ImmutableArray.CreateBuilder<string>(baseList.Types.Count);
+            var builder = ArrayBuilder<string>.GetInstance(baseList.Types.Count);
 
             // It's not sufficient to just store the textual names we see in the inheritance list
             // of a type.  For example if we have:
@@ -937,7 +937,7 @@ private ImmutableArray<string> GetInheritanceNames(BaseListSyntax baseList)
                     AddInheritanceName(builder, baseType.Type, aliasMaps);
                 }
 
-                return builder.ToImmutable();
+                return builder.ToImmutableAndFree();
             }
             finally
             {
@@ -988,7 +988,7 @@ private void ProcessUsings(List<Dictionary<string, string>> aliasMaps, SyntaxLis
         }
 
         private void AddInheritanceName(
-            ImmutableArray<string>.Builder builder, TypeSyntax type,
+            ArrayBuilder<string> builder, TypeSyntax type,
             List<Dictionary<string, string>> aliasMaps)
         {
             var name = GetTypeName(type);

src/Workspaces/Core/Portable/CodeFixes/FixAllOccurrences/FixAllState.FixMultipleDiagnosticProvider.cs

@@ -46,7 +46,7 @@ public FixMultipleDiagnosticProvider(ImmutableDictionary<Project, ImmutableArray
 
             public override Task<IEnumerable<Diagnostic>> GetAllDiagnosticsAsync(Project project, CancellationToken cancellationToken)
             {
-                ImmutableArray<Diagnostic>.Builder allDiagnosticsBuilder = null;
+                var allDiagnosticsBuilder = ArrayBuilder<Diagnostic>.GetInstance();
                 ImmutableArray<Diagnostic> diagnostics;
                 if (!_documentDiagnosticsMap.IsEmpty)
                 {
@@ -54,7 +54,6 @@ public override Task<IEnumerable<Diagnostic>> GetAllDiagnosticsAsync(Project pro
                     {
                         if (_documentDiagnosticsMap.TryGetValue(document, out diagnostics))
                         {
-                            allDiagnosticsBuilder = allDiagnosticsBuilder ?? ImmutableArray.CreateBuilder<Diagnostic>(diagnostics.Length);
                             allDiagnosticsBuilder.AddRange(diagnostics);
                         }
                     }
@@ -62,12 +61,10 @@ public override Task<IEnumerable<Diagnostic>> GetAllDiagnosticsAsync(Project pro
 
                 if (_projectDiagnosticsMap.TryGetValue(project, out diagnostics))
                 {
-                    allDiagnosticsBuilder = allDiagnosticsBuilder ?? ImmutableArray.CreateBuilder<Diagnostic>(diagnostics.Length);
                     allDiagnosticsBuilder.AddRange(diagnostics);
                 }
 
-                IEnumerable<Diagnostic> allDiagnostics = allDiagnosticsBuilder != null ? allDiagnosticsBuilder.ToImmutable() : ImmutableArray<Diagnostic>.Empty;
-                return Task.FromResult(allDiagnostics);
+                return Task.FromResult<IEnumerable<Diagnostic>>(allDiagnosticsBuilder.ToImmutableAndFree());
             }
 
             public override Task<IEnumerable<Diagnostic>> GetDocumentDiagnosticsAsync(Document document, CancellationToken cancellationToken)

src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo_Metadata.cs

@@ -583,16 +583,16 @@ private void EnsureParentsAndChildren(List<string> simpleNames)
 
             private ImmutableArray<BuilderNode> GenerateUnsortedNodes()
             {
-                var unsortedNodes = ImmutableArray.CreateBuilder<BuilderNode>();
+                var unsortedNodes = ArrayBuilder<BuilderNode>.GetInstance();
                 unsortedNodes.Add(new BuilderNode(name: "", parentIndex: RootNodeParentIndex));
 
                 AddUnsortedNodes(unsortedNodes, parentNode: _rootNode, parentIndex: 0);
 
-                return unsortedNodes.ToImmutable();
+                return unsortedNodes.ToImmutableAndFree();
             }
 
             private void AddUnsortedNodes(
-                ImmutableArray<BuilderNode>.Builder unsortedNodes, MetadataNode parentNode, int parentIndex)
+                ArrayBuilder<BuilderNode> unsortedNodes, MetadataNode parentNode, int parentIndex)
             {
                 foreach (var child in _parentToChildren[parentNode])
                 {

src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo_Source.cs

@@ -43,20 +43,20 @@ private static void FreeSymbolMap(MultiDictionary<string, ISymbol> symbolMap)
                 return null;
             }
 
-            var unsortedNodes = ImmutableArray.CreateBuilder<BuilderNode>();
+            var unsortedNodes = ArrayBuilder<BuilderNode>.GetInstance();
             unsortedNodes.Add(new BuilderNode(assembly.GlobalNamespace.Name, RootNodeParentIndex));
 
             GenerateSourceNodes(assembly.GlobalNamespace, unsortedNodes, s_getMembersNoPrivate);
 
             return CreateSymbolTreeInfo(
-                solution, version, filePath, unsortedNodes.ToImmutable(), 
+                solution, version, filePath, unsortedNodes.ToImmutableAndFree(), 
                 inheritanceMap: new OrderPreservingMultiDictionary<string, string>());
         }
 
         // generate nodes for the global namespace an all descendants
         private static void GenerateSourceNodes(
             INamespaceSymbol globalNamespace,
-            ImmutableArray<BuilderNode>.Builder list,
+            ArrayBuilder<BuilderNode> list,
             Action<ISymbol, MultiDictionary<string, ISymbol>> lookup)
         {
             // Add all child members
@@ -89,7 +89,7 @@ private static void FreeSymbolMap(MultiDictionary<string, ISymbol> symbolMap)
             string name,
             int parentIndex,
             MultiDictionary<string, ISymbol>.ValueSet symbolsWithSameName,
-            ImmutableArray<BuilderNode>.Builder list,
+            ArrayBuilder<BuilderNode> list,
             Action<ISymbol, MultiDictionary<string, ISymbol>> lookup)
         {
             var node = new BuilderNode(name, parentIndex);

src/Workspaces/Core/Portable/Shared/Extensions/ISymbolExtensions.cs

@@ -416,7 +416,7 @@ public static ImmutableArray<ITypeSymbol> GetTypeArguments(this ISymbol symbol)
 
         public static ImmutableArray<ITypeSymbol> GetAllTypeArguments(this ISymbol symbol)
         {
-            var results = ImmutableArray.CreateBuilder<ITypeSymbol>();
+            var results = ArrayBuilder<ITypeSymbol>.GetInstance();
             results.AddRange(symbol.GetTypeArguments());
 
             var containingType = symbol.ContainingType;
@@ -426,7 +426,7 @@ public static ImmutableArray<ITypeSymbol> GetAllTypeArguments(this ISymbol symbo
                 containingType = containingType.ContainingType;
             }
 
-            return results.AsImmutable();
+            return results.ToImmutableAndFree();
         }
 
         public static bool IsAttribute(this ISymbol symbol)

src/Workspaces/Core/Portable/Shared/Extensions/SymbolInfoExtensions.cs

@@ -21,10 +21,10 @@ private static ImmutableArray<ISymbol> GetAllSymbolsWorker(this SymbolInfo info)
             }
             else
             {
-                var builder = ImmutableArray.CreateBuilder<ISymbol>(info.CandidateSymbols.Length + 1);
+                var builder = ArrayBuilder<ISymbol>.GetInstance(info.CandidateSymbols.Length + 1);
                 builder.Add(info.Symbol);
                 builder.AddRange(info.CandidateSymbols);
-                return builder.ToImmutable();
+                return builder.ToImmutableAndFree();
             }
         }
 

src/Workspaces/VisualBasic/Portable/LanguageServices/VisualBasicSyntaxFactsService.vb

@@ -925,7 +925,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         End Function
 
         Private Function GetInheritanceNames(typeBlock As TypeBlockSyntax) As ImmutableArray(Of String)
-            Dim builder = ImmutableArray.CreateBuilder(Of String)
+            Dim builder = ArrayBuilder(Of String).GetInstance()
 
             Dim aliasMap = GetAliasMap(typeBlock)
             Try
@@ -937,7 +937,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                     AddInheritanceNames(builder, implementsStatement.Types, aliasMap)
                 Next
 
-                Return builder.ToImmutable()
+                Return builder.ToImmutableAndFree()
             Finally
                 FreeAliasMap(aliasMap)
             End Try
@@ -966,7 +966,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         End Function
 
         Private Sub AddInheritanceNames(
-                builder As ImmutableArray(Of String).Builder,
+                builder As ArrayBuilder(Of String),
                 types As SeparatedSyntaxList(Of TypeSyntax),
                 aliasMap As Dictionary(Of String, String))
 
@@ -976,7 +976,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         End Sub
 
         Private Sub AddInheritanceName(
-                builder As ImmutableArray(Of String).Builder,
+                builder As ArrayBuilder(Of String),
                 typeSyntax As TypeSyntax,
                 aliasMap As Dictionary(Of String, String))
             Dim name = GetTypeName(typeSyntax)