Reduce allocations from creating MissingTokenWithTrivia objects (#75404)

* Reduce allocations from creating MissingTokenWithTrivia objects This method accounts for 0.7% of allocations in the roslyn csharp editing speedometer test profile I'm looking at. In addition to caching tokens < LastTokenWithWellKnownText similar to what is already done, the SyntaxKind.IdentifierToken case is handled as it's very commonly hit too. Local testing of opening LanguageParser and typing in a new method reduced the number of MissingTokenWithTrivia from over 1 million to zero.
dotnet · Oct 8, 2024 · a656d1a · a656d1a
1 parent c625f52
commit a656d1a
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Showing 2 changed files with 20 additions and 2 deletions.
diff --git a/src/Compilers/CSharp/Portable/Syntax/InternalSyntax/SyntaxFactory.cs b/src/Compilers/CSharp/Portable/Syntax/InternalSyntax/SyntaxFactory.cs
@@ -146,7 +146,7 @@ internal static SyntaxToken Token(GreenNode leading, SyntaxKind kind, string tex
 
         internal static SyntaxToken MissingToken(SyntaxKind kind)
         {
-            return SyntaxToken.CreateMissing(kind, null, null);
+            return SyntaxToken.CreateMissing(kind);
         }
 
         internal static SyntaxToken MissingToken(GreenNode leading, SyntaxKind kind, GreenNode trailing)

diff --git a/src/Compilers/CSharp/Portable/Syntax/InternalSyntax/SyntaxToken.cs b/src/Compilers/CSharp/Portable/Syntax/InternalSyntax/SyntaxToken.cs
@@ -76,7 +76,7 @@ internal static SyntaxToken Create(SyntaxKind kind)
                     throw new ArgumentException(string.Format(CSharpResources.ThisMethodCanOnlyBeUsedToCreateTokens, kind), nameof(kind));
                 }
 
-                return CreateMissing(kind, null, null);
+                return CreateMissing(kind);
             }
 
             return s_tokensWithNoTrivia[(int)kind].Value;
@@ -118,6 +118,20 @@ internal static SyntaxToken Create(SyntaxKind kind, GreenNode leading, GreenNode
             return new SyntaxTokenWithTrivia(kind, leading, trailing);
         }
 
+        internal static SyntaxToken CreateMissing(SyntaxKind kind)
+        {
+            if (kind <= LastTokenWithWellKnownText)
+            {
+                return s_missingTokensWithNoTrivia[(int)kind].Value;
+            }
+            else if (kind == SyntaxKind.IdentifierToken)
+            {
+                return s_missingIdentifierTokenWithNoTrivia;
+            }
+
+            return new MissingTokenWithTrivia(kind, leading: null, trailing: null);
+        }
+
         internal static SyntaxToken CreateMissing(SyntaxKind kind, GreenNode leading, GreenNode trailing)
         {
             return new MissingTokenWithTrivia(kind, leading, trailing);
@@ -131,6 +145,9 @@ internal static SyntaxToken CreateMissing(SyntaxKind kind, GreenNode leading, Gr
         private static readonly ArrayElement<SyntaxToken>[] s_tokensWithElasticTrivia = new ArrayElement<SyntaxToken>[(int)LastTokenWithWellKnownText + 1];
         private static readonly ArrayElement<SyntaxToken>[] s_tokensWithSingleTrailingSpace = new ArrayElement<SyntaxToken>[(int)LastTokenWithWellKnownText + 1];
         private static readonly ArrayElement<SyntaxToken>[] s_tokensWithSingleTrailingCRLF = new ArrayElement<SyntaxToken>[(int)LastTokenWithWellKnownText + 1];
+        private static readonly ArrayElement<SyntaxToken>[] s_missingTokensWithNoTrivia = new ArrayElement<SyntaxToken>[(int)LastTokenWithWellKnownText + 1];
+
+        private static readonly SyntaxToken s_missingIdentifierTokenWithNoTrivia = new MissingTokenWithTrivia(SyntaxKind.IdentifierToken, leading: null, trailing: null);
 
         static SyntaxToken()
         {
@@ -140,6 +157,7 @@ static SyntaxToken()
                 s_tokensWithElasticTrivia[(int)kind].Value = new SyntaxTokenWithTrivia(kind, SyntaxFactory.ElasticZeroSpace, SyntaxFactory.ElasticZeroSpace);
                 s_tokensWithSingleTrailingSpace[(int)kind].Value = new SyntaxTokenWithTrivia(kind, null, SyntaxFactory.Space);
                 s_tokensWithSingleTrailingCRLF[(int)kind].Value = new SyntaxTokenWithTrivia(kind, null, SyntaxFactory.CarriageReturnLineFeed);
+                s_missingTokensWithNoTrivia[(int)kind].Value = new MissingTokenWithTrivia(kind, leading: null, trailing: null);
             }
         }