Improve Regex performance (mainly interpreted)

[stephentoub]

This is a follow-on to #271, which improved the performance of Regex, mainly for compiled regular expressions. This PR improves the throughput of interpreted Regexes, those without the RegexOptions.Compiled option.

The primary change here is similar in nature to the primary change for Compiled: generating a fast lookup for ASCII values rather than having to parse/analyze the character class description for each character matched against it. In the Compiled case, we took the time to analyze the first 128 characters and emit a static lookup to make it fast to find the answer for any character < 128. But generating such a lookup table takes time. For Compiled, we're willing to pay that time, because signing up for Compiled is done when you want to maximize throughput at the expense of such upfront costs. We don't have that luxury for non-compiled. Instead, we throw a small additional amount of memory at the problem. Instead of storing 128 bits per character class (one for each character), we store 256 bits per character class: for each character a bit indicating whether we've evaluated it and a bit indicating the result. The first time we encounter a character, we do the more costly evaluation, and then we store back both that we evaluated it and the result; subsequent accesses will see that it was already evaluated and just use the cached result.

A few other, smaller opportunistic changes were also made here based on profiling, including improving some of the codegen around repeated array accesses and inlining a function on a hot path where doing so made an impactful difference. Also a tiny bit of code cleanup as I was touching the relevant functions.

Method	Toolchain	Mean	Error	StdDev	Ratio	Allocated
Email	New	465.6 ns	1.26 ns	1.12 ns	0.78	-
Email	Old	600.5 ns	2.97 ns	2.78 ns	1.00	-
Date	New	242.7 ns	0.43 ns	0.40 ns	0.59	-
Date	Old	414.6 ns	0.52 ns	0.49 ns	1.00	-
IP	New	1,975.4 ns	3.46 ns	3.07 ns	0.77	-
IP	Old	2,573.9 ns	8.53 ns	7.13 ns	1.00	-
Uri	New	311.8 ns	24.92 ns	39.53 ns	0.63	-
Uri	Old	508.8 ns	1.31 ns	1.16 ns	1.00	-
EmailStatic	New	517.3 ns	2.28 ns	2.13 ns	0.80	104 B
EmailStatic	Old	650.2 ns	2.03 ns	1.69 ns	1.00	104 B
DateStatic	New	303.4 ns	0.44 ns	0.39 ns	0.66	104 B
DateStatic	Old	458.3 ns	1.95 ns	1.83 ns	1.00	104 B
IPStatic	New	2,038.7 ns	2.53 ns	2.37 ns	0.75	104 B
IPStatic	Old	2,702.2 ns	22.82 ns	19.05 ns	1.00	104 B
UriStatic	New	341.6 ns	0.55 ns	0.43 ns	0.62	104 B
UriStatic	Old	551.8 ns	1.36 ns	1.13 ns	1.00	104 B
Ctor	New	5,568.8 ns	15.11 ns	12.62 ns	0.99	9792 B
Ctor	Old	5,641.3 ns	41.50 ns	38.81 ns	1.00	9712 B

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Diagnosers;
using BenchmarkDotNet.Running;
using System.Text.RegularExpressions;

public class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssemblies(new[] { typeof(Program).Assembly }).Run(args);
}

[MemoryDiagnoser]
public class Regexes
{
    [Params(RegexOptions.None)] //, RegexOptions.Compiled)]
    public RegexOptions Options { get; set; }

    private Regex _email, _date, _ip, _uri;

    private const string EmailPattern = @"^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,12}|[0-9]{1,3})(\]?)$";
    private const string DatePattern = @"\b(?<month>\d{1,2})/(?<day>\d{1,2})/(?<year>\d{2,4})\b";
    private const string IPPattern = @"(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9])\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9])";
    private const string UriPattern = @"[\w]+://[^/\s?#]+[^\s?#]+(?:\?[^\s#]*)?(?:#[^\s]*)?";

    [GlobalSetup]
    public void Setup()
    {
        _email = new Regex(EmailPattern, Options);
        _date = new Regex(DatePattern, Options);
        _ip = new Regex(IPPattern, Options);
        _uri = new Regex(UriPattern, Options);
    }

    [Benchmark] public void Email() => _email.IsMatch("[email protected]");
    [Benchmark] public void Date() => _date.IsMatch("Today is 11/18/2019");
    [Benchmark] public void IP() => _ip.IsMatch("012.345.678.910");
    [Benchmark] public void Uri() => _uri.IsMatch("http://example.org");

    [Benchmark] public void EmailStatic() => Regex.IsMatch("[email protected]", EmailPattern, Options);
    [Benchmark] public void DateStatic() => Regex.IsMatch("Today is 11/18/2019", DatePattern, Options);
    [Benchmark] public void IPStatic() => Regex.IsMatch("012.345.678.910", IPPattern, Options);
    [Benchmark] public void UriStatic() => Regex.IsMatch("http://example.org", UriPattern, Options);

    [Benchmark] public void Ctor() => new Regex(@"(^(.*)(\(([0-9]+),([0-9]+)\)): )(error|warning) ([A-Z]+[0-9]+) ?: (.*)", Options);
}

cc: @danmosemsft, @ViktorHofer, @davidwrighton, @eerhardt

[eerhardt]

Looks good to me. Just a couple minor nits/questions.

[stephentoub]

Thanks for reviewing, @eerhardt.

[danmoseley]

This is awesome, thanks @stephentoub. Do you think there may much more that can be achieved incrementally?

[stephentoub]

Do you think there may much more that can be achieved incrementally?

I do, e.g. #496