From 8770fb62a36157ed4ca38a16a0283d27321a01a7 Mon Sep 17 00:00:00 2001
From: Fred Silberberg <frsilb@microsoft.com>
Date: Tue, 7 Mar 2023 12:33:04 -0800
Subject: [PATCH] Walk green tree in SyntaxFacts.HasYieldOperations to avoid
 excessive allocations in reported trace (#67221)

* Walk green tree to avoid excessive allocations in reported trace

* Make private

* Remove comment

* Free stack on return

* Include github link for attribute descriptions.
---------

Co-authored-by: Cyrus Najmabadi <cyrusn@microsoft.com>
Co-authored-by: Rikki Gibson <rikkigibson@gmail.com>
---
 .../CSharp/Portable/Syntax/SyntaxFacts.cs     | 62 +++++++++++++------
 1 file changed, 44 insertions(+), 18 deletions(-)

diff --git a/src/Compilers/CSharp/Portable/Syntax/SyntaxFacts.cs b/src/Compilers/CSharp/Portable/Syntax/SyntaxFacts.cs
index e19e0aa498b65..2723d5a623788 100644
--- a/src/Compilers/CSharp/Portable/Syntax/SyntaxFacts.cs
+++ b/src/Compilers/CSharp/Portable/Syntax/SyntaxFacts.cs
@@ -8,6 +8,7 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.PooledObjects;
 using Roslyn.Utilities;
 using static Microsoft.CodeAnalysis.CSharp.SyntaxKind;
 
@@ -543,29 +544,54 @@ internal static bool HasAwaitOperations(SyntaxNode node)
                             });
         }
 
-        internal static bool IsNestedFunction(SyntaxNode child)
+        private static bool IsNestedFunction(SyntaxNode child)
+            => IsNestedFunction(child.Kind());
+
+        private static bool IsNestedFunction(SyntaxKind kind)
+            => kind is SyntaxKind.LocalFunctionStatement
+                or SyntaxKind.AnonymousMethodExpression
+                or SyntaxKind.SimpleLambdaExpression
+                or SyntaxKind.ParenthesizedLambdaExpression;
+
+        [PerformanceSensitive("https://github.com/dotnet/roslyn/pull/66970", Constraint = "Use Green nodes for walking to avoid heavy allocations.")]
+        internal static bool HasYieldOperations(SyntaxNode? node)
         {
-            switch (child.Kind())
+            if (node is null)
+                return false;
+
+            var stack = ArrayBuilder<GreenNode>.GetInstance();
+            stack.Push(node.Green);
+
+            while (stack.Count > 0)
             {
-                case SyntaxKind.LocalFunctionStatement:
-                case SyntaxKind.AnonymousMethodExpression:
-                case SyntaxKind.SimpleLambdaExpression:
-                case SyntaxKind.ParenthesizedLambdaExpression:
+                var current = stack.Pop();
+                Debug.Assert(node.Green == current || current is not Syntax.InternalSyntax.MemberDeclarationSyntax and not Syntax.InternalSyntax.TypeDeclarationSyntax);
+
+                if (current is null)
+                    continue;
+
+                // Do not descend into functions and expressions
+                if (IsNestedFunction((SyntaxKind)current.RawKind) ||
+                    current is Syntax.InternalSyntax.ExpressionSyntax)
+                {
+                    continue;
+                }
+
+                if (current is Syntax.InternalSyntax.YieldStatementSyntax)
+                {
+                    stack.Free();
                     return true;
-                default:
-                    return false;
+                }
+
+                foreach (var child in current.ChildNodesAndTokens())
+                {
+                    if (!child.IsToken)
+                        stack.Push(child);
+                }
             }
-        }
 
-        internal static bool HasYieldOperations(SyntaxNode? node)
-        {
-            // Do not descend into functions and expressions
-            return node is object &&
-                   node.DescendantNodesAndSelf(child =>
-                   {
-                       Debug.Assert(ReferenceEquals(node, child) || child is not (MemberDeclarationSyntax or TypeDeclarationSyntax));
-                       return !IsNestedFunction(child) && !(node is ExpressionSyntax);
-                   }).Any(n => n is YieldStatementSyntax);
+            stack.Free();
+            return false;
         }
 
         internal static bool HasReturnWithExpression(SyntaxNode? node)