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Reimplement LINQ ToList using SegmentedArrayBuilder to reduce allocations #104365

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Merged
merged 7 commits into from
Jul 16, 2024
Merged

Reimplement LINQ ToList using SegmentedArrayBuilder to reduce allocations #104365

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5a1c945
Use SegmentedArrayBuilder in ToList
andrewjsaid Jul 2, 2024
b082e7f
Implement SegmentedArrayBuilder for Select iterators
andrewjsaid Jul 2, 2024
4ff3964
Implement SegmentedArrayBuilder for OfType and SelectMany iterators
andrewjsaid Jul 2, 2024
c49c2a0
Implement SegmentedArrayBuilder for SkipTake and Where iterators
andrewjsaid Jul 2, 2024
730bbe8
Revert change to ToList for non-specialized cases as requested in review
andrewjsaid Jul 16, 2024
c3149b9
Better naming for ToArray/ToList in Select enumerator when size is un…
andrewjsaid Jul 16, 2024
b0bff54
Merge branch 'main' into linq-tolist-stack
eiriktsarpalis Jul 16, 2024
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Implement SegmentedArrayBuilder for SkipTake and Where iterators
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@andrewjsaid
andrewjsaid committed Jul 2, 2024
commit c49c2a0ee2cd905316b80825e2e779ea63d337d9
13 changes: 9 additions & 4 deletions src/libraries/System.Linq/src/System/Linq/SkipTake.SpeedOpt.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -491,25 +491,30 @@ public override TSource[] ToArray()

public override List<TSource> ToList()
{
var list = new List<TSource>();

using (IEnumerator<TSource> en = _source.GetEnumerator())
{
if (SkipBeforeFirst(en) && en.MoveNext())
{
int remaining = Limit - 1; // Max number of items left, not counting the current element.
int comparand = HasLimit ? 0 : int.MinValue; // If we don't have an upper bound, have the comparison always return true.

SegmentedArrayBuilder<TSource>.ScratchBuffer scratch = default;
SegmentedArrayBuilder<TSource> builder = new(scratch);
do
{
remaining--;
list.Add(en.Current);
builder.Add(en.Current);
}
while (remaining >= comparand && en.MoveNext());

List<TSource> result = builder.ToList();
builder.Dispose();

return result;
}
}

return list;
return [];
}

private bool SkipBeforeFirst(IEnumerator<TSource> en) => SkipBefore(_minIndexInclusive, en);
Expand Down
40 changes: 28 additions & 12 deletions src/libraries/System.Linq/src/System/Linq/Where.SpeedOpt.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -55,18 +55,22 @@ public override TSource[] ToArray()

public override List<TSource> ToList()
{
var list = new List<TSource>();
SegmentedArrayBuilder<TSource>.ScratchBuffer scratch = default;
SegmentedArrayBuilder<TSource> builder = new(scratch);

Func<TSource, bool> predicate = _predicate;
foreach (TSource item in _source)
{
if (predicate(item))
{
list.Add(item);
builder.Add(item);
}
}

return list;
List<TSource> result = builder.ToList();
builder.Dispose();

return result;
}

public override TSource? TryGetFirst(out bool found)
Expand Down Expand Up @@ -199,17 +203,21 @@ public static TSource[] ToArray(ReadOnlySpan<TSource> source, Func<TSource, bool

public static List<TSource> ToList(ReadOnlySpan<TSource> source, Func<TSource, bool> predicate)
{
var list = new List<TSource>();
SegmentedArrayBuilder<TSource>.ScratchBuffer scratch = default;
SegmentedArrayBuilder<TSource> builder = new(scratch);

foreach (TSource item in source)
{
if (predicate(item))
{
list.Add(item);
builder.Add(item);
}
}

return list;
List<TSource> result = builder.ToList();
builder.Dispose();

return result;
}

public override TSource? TryGetFirst(out bool found)
Expand Down Expand Up @@ -398,17 +406,21 @@ public static TResult[] ToArray(ReadOnlySpan<TSource> source, Func<TSource, bool

public static List<TResult> ToList(ReadOnlySpan<TSource> source, Func<TSource, bool> predicate, Func<TSource, TResult> selector)
{
var list = new List<TResult>();
SegmentedArrayBuilder<TResult>.ScratchBuffer scratch = default;
SegmentedArrayBuilder<TResult> builder = new(scratch);

foreach (TSource item in source)
{
if (predicate(item))
{
list.Add(selector(item));
builder.Add(selector(item));
}
}

return list;
List<TResult> result = builder.ToList();
builder.Dispose();

return result;
}

public override TResult? TryGetFirst(out bool found) => TryGetFirst(_source, _predicate, _selector, out found);
Expand Down Expand Up @@ -538,19 +550,23 @@ public override TResult[] ToArray()

public override List<TResult> ToList()
{
var list = new List<TResult>();
SegmentedArrayBuilder<TResult>.ScratchBuffer scratch = default;
SegmentedArrayBuilder<TResult> builder = new(scratch);

Func<TSource, bool> predicate = _predicate;
Func<TSource, TResult> selector = _selector;
foreach (TSource item in _source)
{
if (predicate(item))
{
list.Add(selector(item));
builder.Add(selector(item));
}
}

return list;
List<TResult> result = builder.ToList();
builder.Dispose();

return result;
}

public override TResult? TryGetFirst(out bool found)
Expand Down