Improve vectorization of IndexOf(chars, StringComparison.OrdinalIgnoreCase)

[stephentoub]

Use the same general "Algorithm 1: Generic SIMD" that we do for StringComparison.Ordinal, adapted for OrdinalIgnoreCase.

privatestaticreadonlystrings_haystack=newHttpClient().GetStringAsync("https://www.gutenberg.org/files/1661/1661-0.txt").Result;[Params("watson","elementary","holmes","the")]publicstringNeedle{get;set;}[Benchmark]publicintCount(){intcount=0;ReadOnlySpan<char>haystack=s_haystack;while(true){intpos=haystack.IndexOf(Needle,StringComparison.OrdinalIgnoreCase);if(pos<0)break;count++;haystack=haystack.Slice(pos+Needle.Length);}returncount;}

Method	Toolchain	Needle	Mean	Error	StdDev	Ratio
Count	\main\corerun.exe	elementary	580.54 us	3.562 us	2.781 us	1.00
Count	\pr\corerun.exe	elementary	59.37 us	0.447 us	0.397 us	0.10
Count	\main\corerun.exe	holmes	366.58 us	0.607 us	0.568 us	1.00
Count	\pr\corerun.exe	holmes	82.55 us	0.204 us	0.181 us	0.23
Count	\main\corerun.exe	the	547.91 us	1.257 us	1.050 us	1.00
Count	\pr\corerun.exe	the	258.62 us	1.123 us	0.996 us	0.47
Count	\main\corerun.exe	watson	230.76 us	0.550 us	0.514 us	1.00
Count	\pr\corerun.exe	watson	58.24 us	0.448 us	0.419 us	0.25

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Issue Details

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Use the same general "Algorithm 1: Generic SIMD" that we do for StringComparison.Ordinal, adapter for OrdinalIgnoreCase.

[Params("watson","elementary","holmes","the")]publicstringNeedle{get;set;}[Benchmark]publicintCount(){intcount=0;ReadOnlySpan<char>haystack=s_haystack;while(true){intpos=haystack.IndexOf(Needle,StringComparison.OrdinalIgnoreCase);if(pos<0)break;count++;haystack=haystack.Slice(pos+Needle.Length);}returncount;}

Method	Toolchain	Needle	Mean	Error	StdDev	Ratio
Count	\main\corerun.exe	elementary	580.54 us	3.562 us	2.781 us	1.00
Count	\pr\corerun.exe	elementary	59.37 us	0.447 us	0.397 us	0.10
Count	\main\corerun.exe	holmes	366.58 us	0.607 us	0.568 us	1.00
Count	\pr\corerun.exe	holmes	82.55 us	0.204 us	0.181 us	0.23
Count	\main\corerun.exe	the	547.91 us	1.257 us	1.050 us	1.00
Count	\pr\corerun.exe	the	258.62 us	1.123 us	0.996 us	0.47
Count	\main\corerun.exe	watson	230.76 us	0.550 us	0.514 us	1.00
Count	\pr\corerun.exe	watson	58.24 us	0.448 us	0.419 us	0.25

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

[EgorBo]

Very nit: Vector128.BitwiseOr -> |

[stephentoub]

This is just style, right? Happy to change it, just questioning whether it's worth rerunning ci.

[EgorBo]

definitely not worth it 🙂

[tannergooding]

Right its "just style". There is also the general considerations of "methods" vs "operators" (such as precedence and readability) but we're not super consistent today just due to the operators being relatively new.

[EgorBo]

Nice! Assuming we're fine with the overhead for the worst case - it's slightly bigger in case of OrdinalIgnoreCase due to more work + the path to find unique chars is more expensive, but the benefits should outweight that 👍

[stephentoub]

I think it's worth it. It's more expensive to set up than ordinal, but the match validation that happens on every potential match is also more expensive, and this generally lessens the latter. It will regress in cases similar to ordinal regressed, eg where the starting character never matches, but on the balance I expect it'll be a meaningful win. Let's try and see what falls out. :-)