Increase size of Number's small numbers cache, and make it lazy

[stephentoub]

Fixes #76888

[MemoryDiagnoser]
public partial class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    [Benchmark]
    [Arguments(-1)]
    [Arguments(2)]
    [Arguments(20)]
    [Arguments(200)]
    [Arguments(2000)]
    public string Int32ToString(int i) => i.ToString();

    [Benchmark]
    [Arguments(-1)]
    [Arguments(2)]
    [Arguments(20)]
    [Arguments(200)]
    [Arguments(2000)]
    public string Int64ToString(long i) => i.ToString();
}

Method	Toolchain	i	Mean	Error	StdDev	Ratio	Allocated
Int32ToString	\main\corerun.exe	2	1.5308 ns	0.0915 ns	0.0856 ns	1.00	-
Int32ToString	\pr\corerun.exe	2	3.0073 ns	0.1173 ns	0.1826 ns	1.97	-
Int64ToString	\main\corerun.exe	2	2.1372 ns	0.0856 ns	0.0759 ns	1.00	-
Int64ToString	\pr\corerun.exe	2	3.5599 ns	0.1288 ns	0.2042 ns	1.73	-
Int32ToString	\main\corerun.exe	20	9.6048 ns	0.2319 ns	0.2170 ns	1.00	32 B
Int32ToString	\pr\corerun.exe	20	2.7729 ns	0.1113 ns	0.1325 ns	0.29	-
Int64ToString	\main\corerun.exe	20	10.6359 ns	0.2711 ns	0.4058 ns	1.00	32 B
Int64ToString	\pr\corerun.exe	20	3.3825 ns	0.1306 ns	0.2071 ns	0.32	-
Int32ToString	\main\corerun.exe	200	10.1559 ns	0.2582 ns	0.3619 ns	1.00	32 B
Int32ToString	\pr\corerun.exe	200	2.4571 ns	0.0307 ns	0.0256 ns	0.24	-
Int64ToString	\main\corerun.exe	200	11.5714 ns	0.2896 ns	0.5072 ns	1.00	32 B
Int64ToString	\pr\corerun.exe	200	3.5913 ns	0.1289 ns	0.2691 ns	0.31	-
Int32ToString	\main\corerun.exe	2000	10.4373 ns	0.2693 ns	0.3307 ns	1.00	32 B
Int32ToString	\pr\corerun.exe	2000	10.4839 ns	0.2502 ns	0.3588 ns	1.00	32 B
Int64ToString	\main\corerun.exe	2000	11.8617 ns	0.2975 ns	0.5051 ns	1.00	32 B
Int64ToString	\pr\corerun.exe	2000	12.2352 ns	0.2989 ns	0.3198 ns	1.03	32 B
Int32ToString	\main\corerun.exe	-1	18.9890 ns	0.4320 ns	0.9111 ns	1.00	32 B
Int32ToString	\pr\corerun.exe	-1	19.8757 ns	0.4461 ns	0.6254 ns	1.05	32 B
Int64ToString	\main\corerun.exe	-1	18.2829 ns	0.4263 ns	0.9796 ns	1.00	32 B
Int64ToString	\pr\corerun.exe	-1	18.4973 ns	0.4308 ns	0.6448 ns	1.02	32 B

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[jkotas]

I assume that the perf regression for i: 2 is some micro-architecture outlier. I do not see anything in the code that would explain it.

[stephentoub]

I assume that the perf regression for i: 2 is some micro-architecture outlier. I do not see anything in the code that would explain it.

Maybe? I'd assumed it was due to switching to the strings being lazily initialized, so there's now a null check / branch where there wasn't one for single digits.

[jkotas]

I'd assumed it was due to switching to the strings being lazily initialized, so there's now a null check / branch where there wasn't one for single digits.

Yes, there is an extra conditional branch, but it should be perfectly predicted in the microbenchmark run. It is not enough to explain close to 2x slowdown.

[stephentoub]

@BrzVlad, can you validate the interpreter changes here? This PR is replacing the cache that intrinsic was using. If there's something I should be doing instead, please let me know.

[stephentoub]

Spoke offline with Vlad about the interpreter, and we're good to remove this hack (plan was to remove it anyway at some point soon).

[stephentoub]

Failure is #79124