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Enumerable.ToList() Optimization #3429

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Sep 24, 2015
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Enumerable.ToList() Optimization #3429

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118 changes: 109 additions & 9 deletions src/System.Linq/src/System/Linq/Enumerable.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -529,7 +529,7 @@ public override IEnumerable<TResult2> Select<TResult2>(Func<TResult, TResult2> s
}


internal sealed class SelectArrayIterator<TSource, TResult> : Iterator<TResult>, IArrayProvider<TResult>
internal sealed class SelectArrayIterator<TSource, TResult> : Iterator<TResult>, IArrayProvider<TResult>, IListProvider<TResult>
{
private readonly TSource[] _source;
private readonly Func<TSource, TResult> _selector;
Expand Down Expand Up @@ -573,9 +573,20 @@ public TResult[] ToArray()
}
return results;
}

public List<TResult> ToList()
{
TSource[] source = _source;
var results = new List<TResult>(source.Length);
for (int i = 0; i < source.Length; i++)
{
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You need to capture _source into a local here to let JIT optimize the range check. Otherwise JIT must assume that _source may change on every iteration and will not optimize.
results.Add(_selector(source[i]));
}
return results;
}
}

internal sealed class SelectListIterator<TSource, TResult> : Iterator<TResult>, IArrayProvider<TResult>
internal sealed class SelectListIterator<TSource, TResult> : Iterator<TResult>, IArrayProvider<TResult>, IListProvider<TResult>
{
private readonly List<TSource> _source;
private readonly Func<TSource, TResult> _selector;
Expand Down Expand Up @@ -628,9 +639,20 @@ public TResult[] ToArray()
}
return results;
}

public List<TResult> ToList()
{
int count = _source.Count;
var results = new List<TResult>(count);
for (int i = 0; i < count; i++)
{
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for (int i = 0, cnt = _source.Count; i < cnt; i++)
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(You probably want to move the setting of cnt to before constructing the list so you can use the cnt in the ctor call as well.)
results.Add(_selector(_source[i]));
}
return results;
}
}

internal sealed class SelectIListIterator<TSource, TResult> : Iterator<TResult>, IArrayProvider<TResult>
internal sealed class SelectIListIterator<TSource, TResult> : Iterator<TResult>, IArrayProvider<TResult>, IListProvider<TResult>
{
private readonly IList<TSource> _source;
private readonly Func<TSource, TResult> _selector;
Expand Down Expand Up @@ -693,6 +715,17 @@ public TResult[] ToArray()
}
return results;
}

public List<TResult> ToList()
{
int count = _source.Count;
var results = new List<TResult>(count);
for (int i = 0; i < count; i++)
{
results.Add(_selector(_source[i]));
}
return results;
}
}

//public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) {
Expand Down Expand Up @@ -1223,7 +1256,8 @@ public static TSource[] ToArray<TSource>(this IEnumerable<TSource> source)
public static List<TSource> ToList<TSource>(this IEnumerable<TSource> source)
{
if (source == null) throw Error.ArgumentNull("source");
return new List<TSource>(source);
IListProvider<TSource> listProvider = source as IListProvider<TSource>;
return listProvider != null ? listProvider.ToList() : new List<TSource>(source);
}

public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
Expand Down Expand Up @@ -1710,7 +1744,7 @@ public static IEnumerable<int> Range(int start, int count)
return new RangeIterator(start, count);
}

private sealed class RangeIterator : Iterator<int>, IArrayProvider<int>
private sealed class RangeIterator : Iterator<int>, IArrayProvider<int>, IListProvider<int>
{
private readonly int _start;
private readonly int _end;
Expand Down Expand Up @@ -1760,6 +1794,17 @@ public int[] ToArray()

return array;
}

public List<int> ToList()
{
List<int> list = new List<int>(_end - _start);
for (int cur = _start; cur != _end; cur++)
{
list.Add(cur);
}

return list;
}
}

public static IEnumerable<TResult> Repeat<TResult>(TResult element, int count)
Expand All @@ -1768,7 +1813,7 @@ public static IEnumerable<TResult> Repeat<TResult>(TResult element, int count)
return new RepeatIterator<TResult>(element, count);
}

private sealed class RepeatIterator<TResult> : Iterator<TResult>, IArrayProvider<TResult>
private sealed class RepeatIterator<TResult> : Iterator<TResult>, IArrayProvider<TResult>, IListProvider<TResult>
{
private readonly int _count;
private int _sent;
Expand Down Expand Up @@ -1811,6 +1856,14 @@ public TResult[] ToArray()

return array;
}

public List<TResult> ToList()
{
List<TResult> list = new List<TResult>(_count);
for (int i = 0; i != _count; ++i) list.Add(current);

return list;
}
}

public static IEnumerable<TResult> Empty<TResult>()
Expand Down Expand Up @@ -3137,6 +3190,18 @@ internal interface IArrayProvider<TElement>
TElement[] ToArray();
}

/// <summary>
/// An iterator that can produce a <see cref="List{TElement}"/> through an optimized path.
/// </summary>
internal interface IListProvider<TElement>
{
/// <summary>
/// Produce a <see cref="List{TElement}"/> of the sequence through an optimized path.
/// </summary>
/// <returns>The <see cref="List{TElement}"/>.</returns>
List<TElement> ToList();
}

internal class IdentityFunction<TElement>
{
public static Func<TElement, TElement> Instance
Expand All @@ -3162,7 +3227,7 @@ public interface ILookup<TKey, TElement> : IEnumerable<IGrouping<TKey, TElement>
bool Contains(TKey key);
}

public class Lookup<TKey, TElement> : IEnumerable<IGrouping<TKey, TElement>>, ILookup<TKey, TElement>, IArrayProvider<IGrouping<TKey, TElement>>
public class Lookup<TKey, TElement> : IEnumerable<IGrouping<TKey, TElement>>, ILookup<TKey, TElement>, IArrayProvider<IGrouping<TKey, TElement>>, IListProvider<IGrouping<TKey, TElement>>
{
private IEqualityComparer<TKey> _comparer;
private Grouping<TKey, TElement>[] _groupings;
Expand Down Expand Up @@ -3250,6 +3315,21 @@ IGrouping<TKey, TElement>[] IArrayProvider<IGrouping<TKey, TElement>>.ToArray()
return array;
}

List<IGrouping<TKey, TElement>> IListProvider<IGrouping<TKey, TElement>>.ToList()
{
List<IGrouping<TKey, TElement>> list = new List<IGrouping<TKey, TElement>>(_count);
Grouping<TKey, TElement> g = _lastGrouping;
if (g != null)
{
do
{
g = g.next;
list.Add(g);
} while (g != _lastGrouping);
}
return list;
}

public IEnumerable<TResult> ApplyResultSelector<TResult>(Func<TKey, IEnumerable<TElement>, TResult> resultSelector)
{
Grouping<TKey, TElement> g = _lastGrouping;
Expand Down Expand Up @@ -3575,7 +3655,7 @@ IEnumerator IEnumerable.GetEnumerator()
}
}

internal class GroupedEnumerable<TSource, TKey, TElement> : IEnumerable<IGrouping<TKey, TElement>>, IArrayProvider<IGrouping<TKey, TElement>>
internal class GroupedEnumerable<TSource, TKey, TElement> : IEnumerable<IGrouping<TKey, TElement>>, IArrayProvider<IGrouping<TKey, TElement>>, IListProvider<IGrouping<TKey, TElement>>
{
private IEnumerable<TSource> _source;
private Func<TSource, TKey> _keySelector;
Expand Down Expand Up @@ -3608,9 +3688,15 @@ public IGrouping<TKey, TElement>[] ToArray()
IArrayProvider<IGrouping<TKey, TElement>> lookup = Lookup<TKey, TElement>.Create<TSource>(_source, _keySelector, _elementSelector, _comparer);
return lookup.ToArray();
}

public List<IGrouping<TKey, TElement>> ToList()
{
IListProvider<IGrouping<TKey, TElement>> lookup = Lookup<TKey, TElement>.Create<TSource>(_source, _keySelector, _elementSelector, _comparer);
return lookup.ToList();
}
}

internal abstract class OrderedEnumerable<TElement> : IOrderedEnumerable<TElement>, IArrayProvider<TElement>
internal abstract class OrderedEnumerable<TElement> : IOrderedEnumerable<TElement>, IArrayProvider<TElement>, IListProvider<TElement>
{
internal IEnumerable<TElement> source;

Expand Down Expand Up @@ -3643,6 +3729,20 @@ public TElement[] ToArray()
return array;
}

public List<TElement> ToList()
{
Buffer<TElement> buffer = new Buffer<TElement>(source);
int count = buffer.count;
List<TElement> list = new List<TElement>(count);
if (count > 0)
{
int[] map = SortedMap(buffer);
for (int i = 0; i != count; i++) list.Add(buffer.items[map[i]]);
}

return list;
}

internal abstract EnumerableSorter<TElement> GetEnumerableSorter(EnumerableSorter<TElement> next);

IEnumerator IEnumerable.GetEnumerator()
Expand Down
36 changes: 36 additions & 0 deletions src/System.Linq/tests/GroupByTests.cs
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Expand Up @@ -622,5 +622,41 @@ public void GroupingWithResultsToArray()
Assert.Equal(4, groupedArray.Length);
Assert.Equal(source.GroupBy(r => r.Name, (r, e) => e), groupedArray);
}

[Fact]
public void GroupingToList()
{
Record[] source = new Record[]
{
new Record { Name = "Tim", Score = 55 },
new Record { Name = "Chris", Score = 49 },
new Record { Name = "Robert", Score = -100 },
new Record { Name = "Chris", Score = 24 },
new Record { Name = "Prakash", Score = 9 },
new Record { Name = "Tim", Score = 25 }
};

List<IGrouping<string, Record>> groupedList = source.GroupBy(r => r.Name).ToList();
Assert.Equal(4, groupedList.Count);
Assert.Equal(source.GroupBy(r => r.Name), groupedList);
}

[Fact]
public void GroupingWithResultsToList()
{
Record[] source = new Record[]
{
new Record { Name = "Tim", Score = 55 },
new Record { Name = "Chris", Score = 49 },
new Record { Name = "Robert", Score = -100 },
new Record { Name = "Chris", Score = 24 },
new Record { Name = "Prakash", Score = 9 },
new Record { Name = "Tim", Score = 25 }
};

List<IEnumerable<Record>> groupedList = source.GroupBy(r => r.Name, (r, e) => e).ToList();
Assert.Equal(4, groupedList.Count);
Assert.Equal(source.GroupBy(r => r.Name, (r, e) => e), groupedList);
}
}
}
25 changes: 25 additions & 0 deletions src/System.Linq/tests/OrderByTests.cs
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Expand Up @@ -187,6 +187,31 @@ public void OrderedToArray()
Assert.Equal(expected, source.OrderBy(e => e.Score).ToArray());
}

[Fact]
public void OrderedToList()
{
Record[] source = new Record[]
{
new Record { Name = "Tim", Score = 90 },
new Record { Name = "Robert", Score = 90 },
new Record { Name = "Prakash", Score = 90 },
new Record { Name = "Jim", Score = 90 },
new Record { Name = "John", Score = 90 },
new Record { Name = "Albert", Score = 90 },
};
Record[] expected = new Record[]
{
new Record { Name = "Tim", Score = 90 },
new Record { Name = "Robert", Score = 90 },
new Record { Name = "Prakash", Score = 90 },
new Record { Name = "Jim", Score = 90 },
new Record { Name = "John", Score = 90 },
new Record { Name = "Albert", Score = 90 },
};

Assert.Equal(expected, source.OrderBy(e => e.Score).ToList());
}

//FIXME: This will hang with a larger source. Do we want to deal with that case?
[Fact]
public void SurviveBadComparerAlwaysReturnsPositive()
Expand Down
8 changes: 8 additions & 0 deletions src/System.Linq/tests/RangeTests.cs
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Expand Up @@ -35,6 +35,14 @@ public void Range_ToArray_ProduceCorrectResult()
Assert.Equal(i + 1, array[i]);
}

[Fact]
public void Range_ToList_ProduceCorrectResult()
{
var list = Enumerable.Range(1, 100).ToList();
Assert.Equal(list.Count, 100);
for (var i = 0; i < list.Count; i++)
Assert.Equal(i + 1, list[i]);
}

[Fact]
public void Range_ZeroCountLeadToEmptySequence()
Expand Down
9 changes: 9 additions & 0 deletions src/System.Linq/tests/RepeatTests.cs
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Expand Up @@ -35,6 +35,15 @@ public void Repeat_ToArray_ProduceCorrectResult()
Assert.Equal(1, array[i]);
}

[Fact]
public void Repeat_ToList_ProduceCorrectResult()
{
var list = Enumerable.Repeat(1, 100).ToList();
Assert.Equal(list.Count, 100);
for (var i = 0; i < list.Count; i++)
Assert.Equal(1, list[i]);
}

[Fact]
public void Repeat_ProduceSameObject()
{
Expand Down
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