Reduce OrderBy overheads for default comparer

[stephentoub]

If OrderBy is used with a value type key and and a default or no comparer is specified, we can use Comparer<TKey>.Default.Compare to avoid the interface dispatch. This optimization can be taken further, but for now it handles a common set of cases. (We can subsequently look into a variety of improvements, such as a cheaper way to implement a stable sort, doing the sort in-place in the buffered output when conditions are ammenable, extending these checks for using the default comparer into chained OrderBy/ThenBy cases, etc.)

[Params(10, 100, 1_000, 1_000_000)]
public int Length { get; set; }

private int[] _values;

[GlobalSetup]
public void Setup() => _values = Enumerable.Range(0, Length).Reverse().ToArray();

[Benchmark]
public int[] OrderByToArray() => _values.OrderBy(i => i).ToArray();

Method	Toolchain	Length	Mean	Ratio
OrderByToArray	\main\corerun.exe	10	418.8 ns	1.00
OrderByToArray	\pr\corerun.exe	10	314.6 ns	0.75
OrderByToArray	\main\corerun.exe	100	4,291.3 ns	1.00
OrderByToArray	\pr\corerun.exe	100	2,680.5 ns	0.63
OrderByToArray	\main\corerun.exe	1000	71,427.6 ns	1.00
OrderByToArray	\pr\corerun.exe	1000	40,393.7 ns	0.57
OrderByToArray	\main\corerun.exe	1000000	180,572,845.2 ns	1.00
OrderByToArray	\pr\corerun.exe	1000000	96,260,728.2 ns	0.53

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Issue Details

---

If OrderBy is used with a value type key and and a default or no comparer is specified, we can use Comparer<TKey>.Default.Compare to avoid the interface dispatch. This optimization can be taken further, but for now it handles a common set of cases. (We can subsequently look into a variety of improvements, such as a cheaper way to implement a stable sort, doing the sort in-place in the buffered output when conditions are ammenable, extending these checks for using the default comparer into chained OrderBy/ThenBy cases, etc.)

[Params(10, 100, 1_000, 1_000_000)]
public int Length { get; set; }

private int[] _values;

[GlobalSetup]
public void Setup() => _values = Enumerable.Range(0, Length).Reverse().ToArray();

[Benchmark]
public int[] OrderByToArray() => _values.OrderBy(i => i).ToArray();

Method	Toolchain	Length	Mean	Ratio
OrderByToArray	\main\corerun.exe	10	418.8 ns	1.00
OrderByToArray	\pr\corerun.exe	10	314.6 ns	0.75
OrderByToArray	\main\corerun.exe	100	4,291.3 ns	1.00
OrderByToArray	\pr\corerun.exe	100	2,680.5 ns	0.63
OrderByToArray	\main\corerun.exe	1000	71,427.6 ns	1.00
OrderByToArray	\pr\corerun.exe	1000	40,393.7 ns	0.57
OrderByToArray	\main\corerun.exe	1000000	180,572,845.2 ns	1.00
OrderByToArray	\pr\corerun.exe	1000000	96,260,728.2 ns	0.53

Author:	stephentoub
Assignees:	-
Labels:	area-System.Linq, tenet-performance
Milestone:	8.0.0

[eiriktsarpalis]

Thanks