Avoid rebuilding the _relevantIdentifiers set for every document

Author: Exanite

sources/SilkTouch/SilkTouch/Mods/LocationTransformation/LocationTransformationRewriter.cs

@@ -51,14 +51,38 @@ List<LocationTransformer> transformers
 
         // Used to skip symbol lookups
         // Does not handle the omission of the "-Attribute" suffix, but generally, we don't need to transform attributes
-        _relevantIdentifiers = _symbols.Select(s => s.Name).ToHashSet();
+        _relevantIdentifiers = new HashSet<string>(_symbols.Count);
+        foreach (var symbol in _symbols)
+        {
+            _relevantIdentifiers.Add(symbol.Name);
+        }
+    }
+
+    private LocationTransformationRewriter(
+        HashSet<ISymbol> symbols,
+        List<LocationTransformer> transformers,
+        HashSet<string> relevantIdentifiers
+    )
+    {
+        _symbols = symbols;
+        _transformers = transformers;
+        _relevantIdentifiers = relevantIdentifiers;
     }
 
     /// <summary>
     /// Initializes the renamer to work for a new document. Must be called before visiting any nodes.
     /// </summary>
     public void Initialize(SemanticModel semanticModel) => _semanticModel = semanticModel;
 
+    /// <summary>
+    /// Clone this rewriter for purposes of thread safety.
+    /// </summary>
+    /// <remarks>
+    /// This is allowed to return the current instance and share data.
+    /// </remarks>
+    public LocationTransformationRewriter GetThreadSafeCopy() =>
+        new(_symbols, [.. _transformers.Select(t => t.GetThreadSafeCopy())], _relevantIdentifiers);
+
     /// <inheritdoc />
     [return: NotNullIfNotNull("unmodifiedNode")]
     public override SyntaxNode? Visit(SyntaxNode? unmodifiedNode)

sources/SilkTouch/SilkTouch/Mods/LocationTransformation/LocationTransformationUtils.cs

@@ -53,6 +53,7 @@ public static async Task ModifyAllReferencesAsync(
 
         var newDocuments = new ConcurrentDictionary<DocumentId, SyntaxNode>();
         var symbolSet = new HashSet<ISymbol>(symbols, SymbolEqualityComparer.Default);
+        var baseRewriter = new LocationTransformationRewriter(symbolSet, transformers.ToList());
         await Parallel.ForEachAsync(
             documentIds,
             ct,
@@ -73,10 +74,7 @@ await Parallel.ForEachAsync(
                 var semanticModel = compilation.GetSemanticModel(originalRoot.SyntaxTree);
 
                 // Since this is multithreaded, each thread needs their own copy of the rewriter and transformers
-                var rewriter = new LocationTransformationRewriter(
-                    symbolSet,
-                    [.. transformers.Select(t => t.GetThreadSafeCopy())]
-                );
+                var rewriter = baseRewriter.GetThreadSafeCopy();
 
                 rewriter.Initialize(semanticModel);
                 var newRoot = rewriter.Visit(originalRoot);

sources/SilkTouch/SilkTouch/Mods/LocationTransformation/LocationTransformer.cs

@@ -31,8 +31,9 @@ ISymbol symbol
 
     /// <summary>
     /// Clone this location transformer for purposes of thread safety.
-    /// If the location transformer is already thread safe, the location transformer
-    /// does not need to be cloned.
     /// </summary>
+    /// <remarks>
+    /// This is allowed to return the current instance and share data.
+    /// </remarks>
     public abstract LocationTransformer GetThreadSafeCopy();
 }