Improve IndexOfAnyValues throughput for needles with 0

[MihaZupan]

Increases IndexOfAny throughput by 25-40% for values that contain a 0.

Instead of doing "is ascii" detection at the end as a secondary step to rule out false positives, we can effectively merge it into the "pack sources" step in a cheaper way.

Method	Toolchain	Length	Mean	Error	Ratio	Code Size
IndexOfAnyWithZero	main	10000	414.4 ns	1.17 ns	1.38	682 B
IndexOfAnyWithZero	pr	10000	301.2 ns	1.15 ns	1.00	556 B

Codegen difference: https://www.diffchecker.com/DVRMVOkA

The main loop with AVX2

This should help with Regex after #83992, and with ASP.NET's header validation.

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Issue Details

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Increases IndexOfAny throughput by 25-40% for values that contain a 0.

Instead of doing "is ascii" detection at the end as a secondary step to rule out false positives, we can effectively merge it into the "pack sources" step in a cheaper way.

Method	Toolchain	Length	Mean	Error	Ratio	Code Size
IndexOfAnyWithZero	main	10000	414.4 ns	1.17 ns	1.38	682 B
IndexOfAnyWithZero	pr	10000	301.2 ns	1.15 ns	1.00	556 B

Codegen difference: https://www.diffchecker.com/DVRMVOkA

The main loop with AVX2

This should help with Regex after #83992, and with ASP.NET's header validation.

Author:	MihaZupan
Assignees:	MihaZupan
Labels:	area-System.Memory
Milestone:	8.0.0

[stephentoub]

Contributes to #84139

[MihaZupan]

Bump

Can this one be merged?

[sebastienros]

@MihaZupan mind doing a quick benchmark on fortunes to check for this one #86113

crank command before the change:

crank --config https://raw.githubusercontent.com/aspnet/Benchmarks/main/scenarios/database.benchmarks.yml --scenario fortunes --profile aspnet-citrine-win --application.framework net8.0 --application.aspNetCoreVersion 8.0.0-preview.5.23259.4 --application.runtimeVersion 8.0.0-preview.5.23259.2 --application.sdkVersion 8.0.100-preview.5.23259.3

[MihaZupan]

I can check, but I'd be quite surprised if this regressed anything (especially fortunes)

[MihaZupan]

Tried the following commits:

1. 1b56e96 (PR Improve IndexOfAnyValues throughput for needles with 0 #84184)
2. e241509 (commit just before nr. 3)
3. 58a1365 (PR Unroll StringBuilder.Append for const string #85894)

load	1	2		3
Requests/sec	304,458	302,716	-0.57%	281,044	-7.69%
Requests	4,585,264	4,570,922	-0.31%	4,243,602	-7.45%
Bad responses	0	0		0