From 77b4eadb78f36d636afce7ec3ad1633ba67de7e6 Mon Sep 17 00:00:00 2001
From: Todd Grunke <toddgrun@microsoft.com>
Date: Tue, 10 Oct 2023 08:15:39 -0700
Subject: [PATCH 1/3] Reduce ImmutableDictionary allocations in
 CreateCompilationTrackerMap

1) No need to create a builder if _projectIdToTrackerMap is empty
2) No need to create a new ImmutableDictionary if it would end up having the exact same contents as projectIdToTrackerMap
---
 .../Workspace/Solution/SolutionState.cs       | 21 ++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs b/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
index 9282823dfaa2b..f15d17140a2ae 100644
--- a/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
+++ b/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
@@ -1549,12 +1549,27 @@ private static ProjectDependencyGraph CreateDependencyGraph(
 
         private ImmutableDictionary<ProjectId, ICompilationTracker> CreateCompilationTrackerMap(ProjectId changedProjectId, ProjectDependencyGraph dependencyGraph)
         {
-            var builder = ImmutableDictionary.CreateBuilder<ProjectId, ICompilationTracker>();
+            if (_projectIdToTrackerMap.Count == 0)
+                return _projectIdToTrackerMap;
 
+            var newTrackerInfo = new List<KeyValuePair<ProjectId, ICompilationTracker>>();
+            var allReused = true;
             foreach (var (id, tracker) in _projectIdToTrackerMap)
-                builder.Add(id, CanReuse(id) ? tracker : tracker.Fork(tracker.ProjectState, translate: null));
+            {
+                var localTracker = tracker;
+                if (!CanReuse(id))
+                {
+                    localTracker = tracker.Fork(tracker.ProjectState, translate: null);
+                    allReused = false;
+                }
 
-            return builder.ToImmutable();
+                newTrackerInfo.Add(new KeyValuePair<ProjectId, ICompilationTracker>(id, localTracker));
+            }
+
+            if (allReused)
+                return _projectIdToTrackerMap;
+
+            return ImmutableDictionary.CreateRange(newTrackerInfo);
 
             // Returns true if 'tracker' can be reused for project 'id'
             bool CanReuse(ProjectId id)

From 2ac7cd4b254c94f693463db6fa608b723a52adaf Mon Sep 17 00:00:00 2001
From: Todd Grunke <toddgrun@microsoft.com>
Date: Tue, 10 Oct 2023 09:34:16 -0700
Subject: [PATCH 2/3] Use ArrayBuilder instead of allocating a new list each
 time

---
 .../Core/Portable/Workspace/Solution/SolutionState.cs           | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs b/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
index f15d17140a2ae..9d3f91d5671d5 100644
--- a/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
+++ b/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
@@ -1552,7 +1552,7 @@ private ImmutableDictionary<ProjectId, ICompilationTracker> CreateCompilationTra
             if (_projectIdToTrackerMap.Count == 0)
                 return _projectIdToTrackerMap;
 
-            var newTrackerInfo = new List<KeyValuePair<ProjectId, ICompilationTracker>>();
+            var newTrackerInfo = ArrayBuilder<KeyValuePair<ProjectId, ICompilationTracker>>.GetInstance();
             var allReused = true;
             foreach (var (id, tracker) in _projectIdToTrackerMap)
             {

From fe911b1bbdbc9c1b5445fb7fe30bf571c8c43ab6 Mon Sep 17 00:00:00 2001
From: Todd Grunke <toddgrun@microsoft.com>
Date: Tue, 10 Oct 2023 13:15:12 -0700
Subject: [PATCH 3/3] Forgot to add the using around the ArrayBuilder call

---
 .../Core/Portable/Workspace/Solution/SolutionState.cs           | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs b/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
index 9d3f91d5671d5..9f183de780782 100644
--- a/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
+++ b/src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
@@ -1552,7 +1552,7 @@ private ImmutableDictionary<ProjectId, ICompilationTracker> CreateCompilationTra
             if (_projectIdToTrackerMap.Count == 0)
                 return _projectIdToTrackerMap;
 
-            var newTrackerInfo = ArrayBuilder<KeyValuePair<ProjectId, ICompilationTracker>>.GetInstance();
+            using var _ = ArrayBuilder<KeyValuePair<ProjectId, ICompilationTracker>>.GetInstance(_projectIdToTrackerMap.Count, out var newTrackerInfo);
             var allReused = true;
             foreach (var (id, tracker) in _projectIdToTrackerMap)
             {