Vectorize IndexOfAnyExcept for four values

[adamsitnik]

I took a look and the usage of IndexOfAnyExcept and the patterns are following:

• IndexOfAnyExcept(byte) - most frequent
• IndexOfAnyExcept(int), IndexOfAnyExcept(char) - sporadic
• IndexOfAnyExcept(" \t\r\n") - few places

Since the first two got vectorized by @stephentoub in #73488 I've vectorized the 4 values case.

Benchmarks:

publicclassIndexOfAnyExcept{privatestring_whiteSpaces,_noWhiteSpaces;[Params(1,4,16,64,256,1024)]publicintLength{get;set;}[GlobalSetup]publicvoidSetup(){_whiteSpaces=newstring(' ',Length);_noWhiteSpaces=newstring('a',Length);}[Benchmark]publicintImmediateMismatch()=>_noWhiteSpaces.AsSpan().IndexOfAnyExcept(" \t\r\n");[Benchmark]publicintNoMismatch()=>_whiteSpaces.AsSpan().IndexOfAnyExcept(" \t\r\n");}

BenchmarkDotNet=v0.13.1.1845-nightly, OS=Windows 11 (10.0.22000.795/21H2)
AMD Ryzen Threadripper PRO 3945WX 12-Cores, 1 CPU, 24 logical and 12 physical cores
.NET SDK=7.0.100-preview.7.22377.5
[Host] : .NET 7.0.0 (7.0.22.37506), X64 RyuJIT AVX2
Job-OQFSEO : .NET 7.0.0 (42.42.42.42424), X64 RyuJIT AVX2
Job-main : .NET 7.0.0 (42.42.42.42424), X64 RyuJIT AVX2

Method	Job	Length	Mean	Ratio
ImmediateMismatch	Job-PR	1	7.401 ns	1.30
ImmediateMismatch	Job-main	1	5.679 ns	1.00
NoMismatch	Job-PR	1	7.259 ns	1.32
NoMismatch	Job-main	1	5.483 ns	1.00
ImmediateMismatch	Job-PR	4	7.597 ns	1.34
ImmediateMismatch	Job-main	4	5.689 ns	1.00
NoMismatch	Job-PR	4	10.021 ns	0.76
NoMismatch	Job-main	4	13.155 ns	1.00
ImmediateMismatch	Job-PR	16	9.135 ns	1.47
ImmediateMismatch	Job-main	16	6.226 ns	1.00
NoMismatch	Job-PR	16	9.973 ns	0.24
NoMismatch	Job-main	16	41.561 ns	1.00
ImmediateMismatch	Job-PR	64	9.123 ns	1.47
ImmediateMismatch	Job-main	64	6.216 ns	1.00
NoMismatch	Job-PR	64	15.135 ns	0.09
NoMismatch	Job-main	64	164.828 ns	1.00
ImmediateMismatch	Job-PR	256	9.126 ns	1.47
ImmediateMismatch	Job-main	256	6.196 ns	1.00
NoMismatch	Job-PR	256	31.836 ns	0.05
NoMismatch	Job-main	256	642.908 ns	1.00
ImmediateMismatch	Job-PR	1024	9.128 ns	1.48
ImmediateMismatch	Job-main	1024	6.153 ns	1.00
NoMismatch	Job-PR	1024	104.512 ns	0.04
NoMismatch	Job-main	1024	2,534.292 ns	1.00

It's clearly a tradeoff:

• for all strings with immediate mismatch, the method has regressed by 2-3ns
• same goes for very short strings with no mismatch
• for other cases, when there is no mismatch the longer the string the bigger the gain

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Issue Details

---

I took a look and the usage of IndexOfAnyExcept and the patterns are following:

• IndexOfAnyExcept(byte) - most frequent
• IndexOfAnyExcept(int), IndexOfAnyExcept(char) - sporadic
• IndexOfAnyExcept(" \t\r\n") - few places

Since the first two got vectorized by @stephentoub in #73488 I've vectorized the 4 values case.

Benchmarks:

publicclassIndexOfAnyExcept{privatestring_whiteSpaces,_noWhiteSpaces;[Params(1,4,16,64,256,1024)]publicintLength{get;set;}[GlobalSetup]publicvoidSetup(){_whiteSpaces=newstring(' ',Length);_noWhiteSpaces=newstring('a',Length);}[Benchmark]publicintImmediateMismatch()=>_noWhiteSpaces.AsSpan().IndexOfAnyExcept(" \t\r\n");[Benchmark]publicintNoMismatch()=>_whiteSpaces.AsSpan().IndexOfAnyExcept(" \t\r\n");}

BenchmarkDotNet=v0.13.1.1845-nightly, OS=Windows 11 (10.0.22000.795/21H2)
AMD Ryzen Threadripper PRO 3945WX 12-Cores, 1 CPU, 24 logical and 12 physical cores
.NET SDK=7.0.100-preview.7.22377.5
[Host] : .NET 7.0.0 (7.0.22.37506), X64 RyuJIT AVX2
Job-OQFSEO : .NET 7.0.0 (42.42.42.42424), X64 RyuJIT AVX2
Job-main : .NET 7.0.0 (42.42.42.42424), X64 RyuJIT AVX2

Method	Job	Length	Mean	Ratio
ImmediateMismatch	Job-PR	1	7.401 ns	1.30
ImmediateMismatch	Job-main	1	5.679 ns	1.00
NoMismatch	Job-PR	1	7.259 ns	1.32
NoMismatch	Job-main	1	5.483 ns	1.00
ImmediateMismatch	Job-PR	4	7.597 ns	1.34
ImmediateMismatch	Job-main	4	5.689 ns	1.00
NoMismatch	Job-PR	4	10.021 ns	0.76
NoMismatch	Job-main	4	13.155 ns	1.00
ImmediateMismatch	Job-PR	16	9.135 ns	1.47
ImmediateMismatch	Job-main	16	6.226 ns	1.00
NoMismatch	Job-PR	16	9.973 ns	0.24
NoMismatch	Job-main	16	41.561 ns	1.00
ImmediateMismatch	Job-PR	64	9.123 ns	1.47
ImmediateMismatch	Job-main	64	6.216 ns	1.00
NoMismatch	Job-PR	64	15.135 ns	0.09
NoMismatch	Job-main	64	164.828 ns	1.00
ImmediateMismatch	Job-PR	256	9.126 ns	1.47
ImmediateMismatch	Job-main	256	6.196 ns	1.00
NoMismatch	Job-PR	256	31.836 ns	0.05
NoMismatch	Job-main	256	642.908 ns	1.00
ImmediateMismatch	Job-PR	1024	9.128 ns	1.48
ImmediateMismatch	Job-main	1024	6.153 ns	1.00
NoMismatch	Job-PR	1024	104.512 ns	0.04
NoMismatch	Job-main	1024	2,534.292 ns	1.00

It's clearly a tradeoff:

• for all strings with immediate mismatch, the method has regressed by 2-3ns
• same goes for very short strings with no mismatch
• for other cases, when there is no mismatch the longer the string the bigger the gain

Author:	adamsitnik
Assignees:	-
Labels:	area-System.Memory, tenet-performance
Milestone:	7.0.0

[danmoseley]

Some pretty nice improvements!

[adamsitnik]

The CI did not start... I am going to close and re-open the PR

[stephentoub]

Nit: (don't restart CI just for this)

Suggested change

	case4:// common for searching whitespaces
	case4:// common for searching ASCII whitespaces

[stephentoub]

There are many other methods in this type, whereas this "ComputeIndex" is only relevant to LastIndexOfExcept. Consider renaming it accordingly.

[stephentoub]

Thanks!

[adamsitnik]

@stephentoub Since I currently can't merge #73768, I am going to merge this PR now and address your feedback later (renaming ComputeIndex to ComputeFirstIndex). Normally I would do it first, but we have limited time ;)