Skip to content

Perf: restore O(N+M) item filtering in Lookup.GetItems #13688

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
JanProvaznik wants to merge 5 commits into
base: main
Choose a base branch
from
Open

Perf: restore O(N+M) item filtering in Lookup.GetItems #13688

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
94da6c6
Perf: restore O(N+M) item filtering in Lookup.GetItems
JanProvaznik May 5, 2026
13e0265
Address review: convert assertions to Shouldly, add no-op-removes and…
JanProvaznik May 5, 2026
3a541ea
Merge branch 'main' into dev/janpro/lookup-getitems-perf-fix
JanProvaznik May 7, 2026
a70faba
Address PR review: itemsCount sizing, named threshold, isolated bench…
JanProvaznik May 7, 2026
6e5db5e
Simplify GetItems: always use HashSet for removes (no threshold)
JanProvaznik May 7, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
297 changes: 297 additions & 0 deletions src/Build.UnitTests/BackEnd/Lookup_Tests.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
using Microsoft.Build.Collections;
using Microsoft.Build.Execution;
using Microsoft.Build.Framework;
using Shouldly;
using Xunit;

#nullable disable
Expand Down Expand Up @@ -1282,6 +1283,302 @@ public void ModifiedProperty()
Assert.Equal("v4", lookup.GetProperty("p1").EvaluatedValue);
Assert.Equal("v4", group["p1"].EvaluatedValue);
}

/// <summary>
/// Regression coverage for the perf fix in <see cref="Lookup.GetItems"/> when many
/// items are removed across batches: the result must still contain exactly the items
/// that were not removed, regardless of whether the implementation uses the
/// linear-scan fast path or the HashSet path.
/// </summary>
[Fact]
public void GetItemsAfterManyBatchedRemoves_ReturnsCorrectItems()
{
ProjectInstance project = ProjectHelpers.CreateEmptyProjectInstance();
ItemDictionary<ProjectItemInstance> table1 = new ItemDictionary<ProjectItemInstance>();
const string itemType = "i";
const int baseCount = 200;
const int batchCount = 50; // 50 batches × 4 = 200 removes total → exercises HashSet path
const int batchSize = 4;

var allItems = new List<ProjectItemInstance>(baseCount);
for (int i = 0; i < baseCount; i++)
{
var item = new ProjectItemInstance(project, itemType, $"item_{i}", project.FullPath);
table1.Add(item);
allItems.Add(item);
}

Lookup lookup = LookupHelpers.CreateLookup(table1);
lookup.EnterScope("x");

var removedSet = new HashSet<ProjectItemInstance>();
for (int b = 0; b < batchCount; b++)
{
var batch = new List<ProjectItemInstance>(batchSize);
for (int k = 0; k < batchSize; k++)
{
int idx = b * batchSize + k;
batch.Add(allItems[idx]);
removedSet.Add(allItems[idx]);
}
lookup.RemoveItems(itemType, batch);
}

ICollection<ProjectItemInstance> remaining = lookup.GetItems(itemType);

remaining.Count.ShouldBe(baseCount - (batchCount * batchSize));
foreach (ProjectItemInstance item in remaining)
{
removedSet.ShouldNotContain(item);
}
// And no expected-remaining item is missing
for (int i = batchCount * batchSize; i < baseCount; i++)
{
remaining.ShouldContain(allItems[i]);
}
}

/// <summary>
/// Effective output is independent of how many phantom (no-op) removes are mixed
/// with the real ones. Whether the implementation uses a small or large remove set
/// internally must not change which items survive.
/// </summary>
[Fact]
public void GetItems_PhantomRemovesDoNotChangeResult()
{
const int baseCount = 50;
const int realRemoveCount = 5;
const string itemType = "i";

// Build items once and share between both runs so the resulting collections
// contain the same ProjectItemInstance references, allowing reference-equal
// set comparison.
ProjectInstance project = ProjectHelpers.CreateEmptyProjectInstance();
var allItems = new List<ProjectItemInstance>(baseCount);
for (int i = 0; i < baseCount; i++)
{
allItems.Add(new ProjectItemInstance(project, itemType, $"item_{i}", project.FullPath));
}

// Phantom (no-op) remove references padding the second run.
var phantoms = new List<ProjectItemInstance>();
for (int i = 0; i < 20; i++)
{
phantoms.Add(new ProjectItemInstance(project, itemType, $"phantom_{i}", project.FullPath));
}

ICollection<ProjectItemInstance> noPhantoms = RunWith(allItems, [], realRemoveCount, itemType);
ICollection<ProjectItemInstance> withPhantoms = RunWith(allItems, phantoms, realRemoveCount, itemType);

noPhantoms.Count.ShouldBe(baseCount - realRemoveCount);
withPhantoms.Count.ShouldBe(baseCount - realRemoveCount);
// Reference-equal set comparison: both runs must return the exact same items.
new HashSet<ProjectItemInstance>(withPhantoms).SetEquals(noPhantoms).ShouldBeTrue();

static ICollection<ProjectItemInstance> RunWith(
List<ProjectItemInstance> allItems,
List<ProjectItemInstance> phantomRemoves,
int realRemoveCount,
string itemType)
{
var table = new ItemDictionary<ProjectItemInstance>();
foreach (var item in allItems)
{
table.Add(item);
}

Lookup lookup = LookupHelpers.CreateLookup(table);
lookup.EnterScope("x");

var toRemove = new List<ProjectItemInstance>(realRemoveCount + phantomRemoves.Count);
for (int i = 0; i < realRemoveCount; i++)
{
toRemove.Add(allItems[i]);
}
toRemove.AddRange(phantomRemoves);

lookup.RemoveItems(itemType, toRemove);
return lookup.GetItems(itemType);
}
}

/// <summary>
/// Verifies that GetItems uses reference equality (matching pre-#12320 behavior).
/// Two different <see cref="ProjectItemInstance"/> instances with identical
/// EvaluatedInclude must be treated as distinct: removing one must not remove the other.
/// </summary>
[Fact]
public void GetItems_RemoveUsesReferenceEquality_NotValueEquality()
{
ProjectInstance project = ProjectHelpers.CreateEmptyProjectInstance();
ItemDictionary<ProjectItemInstance> table1 = new ItemDictionary<ProjectItemInstance>();
const string itemType = "i";
const string sharedSpec = "duplicate.cpp";

// Many items so the HashSet path is exercised
var allItems = new List<ProjectItemInstance>();
for (int i = 0; i < 30; i++)
{
var item = new ProjectItemInstance(project, itemType, sharedSpec, project.FullPath);
table1.Add(item);
allItems.Add(item);
}

Lookup lookup = LookupHelpers.CreateLookup(table1);
lookup.EnterScope("x");

// Remove only the first 10 references, even though all share the same EvaluatedInclude
var toRemove = allItems.Take(10).ToList();
lookup.RemoveItems(itemType, toRemove);

ICollection<ProjectItemInstance> remaining = lookup.GetItems(itemType);

// Exactly the 20 untouched references should remain
remaining.Count.ShouldBe(20);
for (int i = 0; i < 10; i++)
{
remaining.ShouldNotContain(allItems[i]);
}
for (int i = 10; i < 30; i++)
{
remaining.ShouldContain(allItems[i]);
}
}

/// <summary>
/// Merged-subscope variant of <see cref="GetItemsAfterManyBatchedRemoves_ReturnsCorrectItems"/>:
/// each batch lives in a child scope that is then merged into the outer scope, mirroring
/// how batched intrinsic-task removes accumulate. Exercises the HashSet path with
/// removes coming from multiple scope levels (multiple lists in <c>allRemoves</c>).
/// </summary>
[Fact]
public void GetItemsAfterMergedSubScopeRemoves_ReturnsCorrectItems()
{
ProjectInstance project = ProjectHelpers.CreateEmptyProjectInstance();
ItemDictionary<ProjectItemInstance> table1 = new ItemDictionary<ProjectItemInstance>();
const string itemType = "i";
const int baseCount = 100;
const int batchCount = 20;
const int batchSize = 3;

var allItems = new List<ProjectItemInstance>(baseCount);
for (int i = 0; i < baseCount; i++)
{
var item = new ProjectItemInstance(project, itemType, $"item_{i}", project.FullPath);
table1.Add(item);
allItems.Add(item);
}

Lookup lookup = LookupHelpers.CreateLookup(table1);
Lookup.Scope outer = lookup.EnterScope("outer");

for (int b = 0; b < batchCount; b++)
{
Lookup.Scope inner = lookup.EnterScope("batch");

var batch = new List<ProjectItemInstance>(batchSize);
for (int k = 0; k < batchSize; k++)
{
batch.Add(allItems[b * batchSize + k]);
}
lookup.RemoveItems(itemType, batch);
inner.LeaveScope();
}

ICollection<ProjectItemInstance> remaining = lookup.GetItems(itemType);

remaining.Count.ShouldBe(baseCount - (batchCount * batchSize));
for (int i = 0; i < batchCount * batchSize; i++)
{
remaining.ShouldNotContain(allItems[i]);
}
for (int i = batchCount * batchSize; i < baseCount; i++)
{
remaining.ShouldContain(allItems[i]);
}

outer.LeaveScope();
}

/// <summary>
/// Removes that don't match anything in the base group must be no-ops: the original
/// items must all survive. Exercises the HashSet path with totalRemoves above the
/// threshold while none of the removes correspond to existing items.
/// </summary>
[Fact]
public void GetItems_RemovesNotInGroup_AreNoOps()
{
ProjectInstance project = ProjectHelpers.CreateEmptyProjectInstance();
ItemDictionary<ProjectItemInstance> table1 = new ItemDictionary<ProjectItemInstance>();
const string itemType = "i";

var originalItems = new List<ProjectItemInstance>();
for (int i = 0; i < 30; i++)
{
var item = new ProjectItemInstance(project, itemType, $"original_{i}", project.FullPath);
table1.Add(item);
originalItems.Add(item);
}

// Build 20 distinct ProjectItemInstance references that were never added to table1.
var phantomRemoves = new List<ProjectItemInstance>();
for (int i = 0; i < 20; i++)
{
phantomRemoves.Add(new ProjectItemInstance(project, itemType, $"phantom_{i}", project.FullPath));
}

Lookup lookup = LookupHelpers.CreateLookup(table1);
lookup.EnterScope("x");
lookup.RemoveItems(itemType, phantomRemoves);

ICollection<ProjectItemInstance> remaining = lookup.GetItems(itemType);

remaining.Count.ShouldBe(30);
foreach (var original in originalItems)
{
remaining.ShouldContain(original);
}
}

/// <summary>
/// The HashSet path filters both <c>groupFound</c> AND <c>allAdds</c>. This test
/// covers the adds branch: add many new items, then remove a subset (above threshold)
/// and verify exactly the unremoved adds survive in the GetItems result.
/// </summary>
[Fact]
public void GetItems_RemoveSubsetOfAdds_ReturnsRemainingAdds()
{
ProjectInstance project = ProjectHelpers.CreateEmptyProjectInstance();
// Empty base table: groupFound will be empty, so the HashSet path applies only to adds.
Lookup lookup = LookupHelpers.CreateLookup(new ItemDictionary<ProjectItemInstance>());
const string itemType = "i";

lookup.EnterScope("x");

var addedItems = new List<ProjectItemInstance>();
for (int i = 0; i < 20; i++)
{
var item = new ProjectItemInstance(project, itemType, $"add_{i}", project.FullPath);
addedItems.Add(item);
lookup.AddNewItem(item);
}

// Remove 15 of the adds → totalRemoves > 8 → HashSet path exercised on the adds branch.
var toRemove = addedItems.Take(15).ToList();
lookup.RemoveItems(itemType, toRemove);

ICollection<ProjectItemInstance> remaining = lookup.GetItems(itemType);

remaining.Count.ShouldBe(5);
for (int i = 0; i < 15; i++)
{
remaining.ShouldNotContain(addedItems[i]);
}
for (int i = 15; i < 20; i++)
{
remaining.ShouldContain(addedItems[i]);
}
}
}

internal sealed class LookupHelpers
Expand Down
1 change: 1 addition & 0 deletions src/Build/AssemblyInfo.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@
[assembly: InternalsVisibleTo("Microsoft.Build.UnitTests.Shared, PublicKey=002400000480000094000000060200000024000052534131000400000100010015c01ae1f50e8cc09ba9eac9147cf8fd9fce2cfe9f8dce4f7301c4132ca9fb50ce8cbf1df4dc18dd4d210e4345c744ecb3365ed327efdbc52603faa5e21daa11234c8c4a73e51f03bf192544581ebe107adee3a34928e39d04e524a9ce729d5090bfd7dad9d10c722c0def9ccc08ff0a03790e48bcd1f9b6c476063e1966a1c4")]
[assembly: InternalsVisibleTo("Microsoft.Build.Tasks.Cop, PublicKey=002400000480000094000000060200000024000052534131000400000100010015c01ae1f50e8cc09ba9eac9147cf8fd9fce2cfe9f8dce4f7301c4132ca9fb50ce8cbf1df4dc18dd4d210e4345c744ecb3365ed327efdbc52603faa5e21daa11234c8c4a73e51f03bf192544581ebe107adee3a34928e39d04e524a9ce729d5090bfd7dad9d10c722c0def9ccc08ff0a03790e48bcd1f9b6c476063e1966a1c4")]
[assembly: InternalsVisibleTo("Microsoft.Build.BuildCheck.UnitTests, PublicKey=002400000480000094000000060200000024000052534131000400000100010015c01ae1f50e8cc09ba9eac9147cf8fd9fce2cfe9f8dce4f7301c4132ca9fb50ce8cbf1df4dc18dd4d210e4345c744ecb3365ed327efdbc52603faa5e21daa11234c8c4a73e51f03bf192544581ebe107adee3a34928e39d04e524a9ce729d5090bfd7dad9d10c722c0def9ccc08ff0a03790e48bcd1f9b6c476063e1966a1c4")]
[assembly: InternalsVisibleTo("MSBuild.Benchmarks, PublicKey=002400000480000094000000060200000024000052534131000400000100010007d1fa57c4aed9f0a32e84aa0faefd0de9e8fd6aec8f87fb03766c834c99921eb23be79ad9d5dcc1dd9ad236132102900b723cf980957fc4e177108fc607774f29e8320e92ea05ece4e821c0a5efe8f1645c4c0c93c1ab99285d622caa652c1dfad63d745d6f2de5f17e5eaf0fc4963d261c8a12436518206dc093344d5ad293")]
// DO NOT expose Internals to "Microsoft.Build.UnitTests.OM.OrcasCompatibility" as this assembly is supposed to only see public interface

// This will enable passing the SafeDirectories flag to any P/Invoke calls/implementations within the assembly,
Expand Down
Loading