Update perf notes based on a 35k line file

Roslyn's src\Compilers\VisualBasic\Portable\Generated\Syntax.xml.Syntax.Generated.vb

Author: GrahamTheCoder

ICSharpCode.CodeConverter/CSharp/VisualBasicConverter.cs

@@ -33,6 +33,7 @@ public static async Task<SyntaxNode> ConvertCompilationTree(Document document,
             var converted = (CSS.CompilationUnitSyntax)await root.AcceptAsync(visualBasicSyntaxVisitor.TriviaConvertingDeclarationVisitor);
 
             try {
+                // This call is very expensive for large documents. Should look for a more performant version, e.g. Is NormalizeWhitespace good enough?
                 converted = (CSS.CompilationUnitSyntax)Formatter.Format(converted, document.Project.Solution.Workspace);
                 return LineTriviaMapper.MapSourceTriviaToTarget(root, converted);
             } catch (Exception) { //TODO log

ICSharpCode.CodeConverter/Shared/LineTriviaMapper.cs

@@ -21,7 +21,7 @@ internal class LineTriviaMapper
         private readonly List<SyntaxTriviaList> _trailingTriviaCarriedOver = new List<SyntaxTriviaList>();
         private readonly Dictionary<SyntaxToken, (List<IReadOnlyCollection<SyntaxTrivia>> Leading, List<IReadOnlyCollection<SyntaxTrivia>> Trailing)> _targetTokenToTrivia = new Dictionary<SyntaxToken, (List<IReadOnlyCollection<SyntaxTrivia>>, List<IReadOnlyCollection<SyntaxTrivia>>)>();
 
-        public LineTriviaMapper(SyntaxNode source, TextLineCollection sourceLines, SyntaxNode target, TextLineCollection targetLines, Dictionary<int, TextLine> targetLeadingTextLineFromSourceLine, Dictionary<int, TextLine> targetTrailingTextLineFromSourceLine)
+        private LineTriviaMapper(SyntaxNode source, TextLineCollection sourceLines, SyntaxNode target, TextLineCollection targetLines, Dictionary<int, TextLine> targetLeadingTextLineFromSourceLine, Dictionary<int, TextLine> targetTrailingTextLineFromSourceLine)
         {
             _source = source;
             _sourceLines = sourceLines;
@@ -69,10 +69,6 @@ private static int GetPosition((SyntaxNodeOrToken Node, int SourceLineIndex, str
             ).ToLookup(n => n.SourceLineIndex, n => n);
         }
 
-        /// <remarks>
-        /// Possible future improvements:
-        /// * Performance: Probably faster to find tokens starting from position of last replaced token rather than from the root node each time
-        /// </remarks>
         private SyntaxNode GetTargetWithSourceTrivia()
         {
             // Reverse iterate to ensure trivia never ends up after the place it came from (consider #if directive or opening brace of method)

ICSharpCode.CodeConverter/VB/CSharpConverter.cs

@@ -39,6 +39,7 @@ public static async Task<SyntaxNode> ConvertCompilationTree(Document document,
             var converted = (VBSyntax.CompilationUnitSyntax)root.Accept(visualBasicSyntaxVisitor.TriviaConvertingVisitor);
 
             try {
+                // This call is very expensive for large documents. Should look for a more performant version, e.g. Is NormalizeWhitespace good enough?
                 converted = (VBSyntax.CompilationUnitSyntax)Formatter.Format(converted, document.Project.Solution.Workspace);
                 return LineTriviaMapper.MapSourceTriviaToTarget(root, converted);
             } catch (Exception) { //TODO log