Fix perf regressions in Utf8Formatter for integers

[stephentoub]

When I added UTF8 support to the core numeric types, I also just routed Utf8Formatter to use the public TryFormat API on each type. That, however, regressed some microbenchmarks due to a) going from StandardFormat to a ReadOnlySpan<char> format and then parsing it back out and b) removing some of the inlining that was there previously. This change puts back into Utf8Formatter.TryFormat the handling of the format and then delegating to the relevant helpers that already exist rather than always going through the public entrypoint (it doesn't do so for 'n', but that's also much rarer to use on a hot path and is also in general more expensive).

private byte[] _buffer = new byte[100];

[Benchmark]
[Arguments(42)]
public bool TryFormatInt32_Default(int value) => Utf8Formatter.TryFormat(value, _buffer, out _);

[Benchmark]
[Arguments(123L)]
public bool TryFormatInt64_Default(long value) => Utf8Formatter.TryFormat(value, _buffer, out _);

[Benchmark]
[Arguments(12345UL)]
public bool TryFormatUInt64_Default(ulong value) => Utf8Formatter.TryFormat(value, _buffer, out _);

[Benchmark]
[Arguments(42)]
public bool TryFormatInt32_D2(int value) => Utf8Formatter.TryFormat(value, _buffer, out _, new StandardFormat('D', 2));

[Benchmark]
[Arguments(0x1234UL)]
public bool TryFormatUInt64_X4(ulong value) => Utf8Formatter.TryFormat(value, _buffer, out _, new StandardFormat('X', 4));

[Benchmark]
[Arguments(long.MinValue)]
public bool TryFormatInt64_X(long value) => Utf8Formatter.TryFormat(value, _buffer, out _, new StandardFormat('X'));

Method	Runtime	value	Mean	Error	StdDev	Ratio	Code Size
TryFormatInt64_X	main	-9223372036854775808	29.905 ns	0.6288 ns	1.0154 ns	1.51	2,545 B
TryFormatInt64_X	pr	-9223372036854775808	13.156 ns	0.2904 ns	0.4607 ns	0.67	210 B
TryFormatInt64_X	.NET 7.0	-9223372036854775808	19.803 ns	0.4241 ns	0.6082 ns	1.00	294 B
TryFormatInt64_Default	main	123	10.610 ns	0.1336 ns	0.1250 ns	1.62	974 B
TryFormatInt64_Default	pr	123	8.754 ns	0.1467 ns	0.1225 ns	1.34	1,167 B
TryFormatInt64_Default	.NET 7.0	123	6.558 ns	0.1536 ns	0.1508 ns	1.00	829 B
TryFormatUInt64_Default	main	12345	10.376 ns	0.2275 ns	0.2337 ns	1.41	608 B
TryFormatUInt64_Default	pr	12345	5.027 ns	0.0532 ns	0.0498 ns	0.68	318 B
TryFormatUInt64_Default	.NET 7.0	12345	7.379 ns	0.0931 ns	0.0825 ns	1.00	458 B
TryFormatInt32_Default	main	42	9.973 ns	0.0832 ns	0.0737 ns	1.78	964 B
TryFormatInt32_Default	pr	42	2.933 ns	0.0472 ns	0.0442 ns	0.52	348 B
TryFormatInt32_Default	.NET 7.0	42	5.609 ns	0.0647 ns	0.0574 ns	1.00	829 B
TryFormatInt32_D2	main	42	20.623 ns	0.1623 ns	0.1518 ns	3.26	2,438 B
TryFormatInt32_D2	pr	42	4.125 ns	0.1098 ns	0.0917 ns	0.65	573 B
TryFormatInt32_D2	.NET 7.0	42	6.340 ns	0.0438 ns	0.0366 ns	1.00	581 B
TryFormatUInt64_X4	main	4660	21.726 ns	0.4386 ns	0.3662 ns	3.69	2,030 B
TryFormatUInt64_X4	pr	4660	6.411 ns	0.0568 ns	0.0474 ns	1.09	257 B
TryFormatUInt64_X4	.NET 7.0	4660	5.841 ns	0.1648 ns	0.1897 ns	1.00	290 B

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Issue Details

---

When I added UTF8 support to the core numeric types, I also just routed Utf8Formatter to use the public TryFormat API on each type. That, however, regressed some microbenchmarks due to a) going from StandardFormat to a ReadOnlySpan<char> format and then parsing it back out and b) removing some of the inlining that was there previously. This change puts back into Utf8Formatter.TryFormat the handling of the format and then delegating to the relevant helpers that already exist rather than always going through the public entrypoint (it doesn't do so for 'n', but that's also much rarer to use on a hot path and is also in general more expensive).

private byte[] _buffer = new byte[100];

[Benchmark]
[Arguments(42)]
public bool TryFormatInt32_Default(int value) => Utf8Formatter.TryFormat(value, _buffer, out _);

[Benchmark]
[Arguments(123L)]
public bool TryFormatInt64_Default(long value) => Utf8Formatter.TryFormat(value, _buffer, out _);

[Benchmark]
[Arguments(12345UL)]
public bool TryFormatUInt64_Default(ulong value) => Utf8Formatter.TryFormat(value, _buffer, out _);

[Benchmark]
[Arguments(42)]
public bool TryFormatInt32_D2(int value) => Utf8Formatter.TryFormat(value, _buffer, out _, new StandardFormat('D', 2));

[Benchmark]
[Arguments(0x1234UL)]
public bool TryFormatUInt64_X4(ulong value) => Utf8Formatter.TryFormat(value, _buffer, out _, new StandardFormat('X', 4));

[Benchmark]
[Arguments(long.MinValue)]
public bool TryFormatInt64_X(long value) => Utf8Formatter.TryFormat(value, _buffer, out _, new StandardFormat('X'));

Method	Runtime	value	Mean	Error	StdDev	Ratio	Code Size
TryFormatInt64_X	main	-9223372036854775808	29.905 ns	0.6288 ns	1.0154 ns	1.51	2,545 B
TryFormatInt64_X	pr	-9223372036854775808	13.156 ns	0.2904 ns	0.4607 ns	0.67	210 B
TryFormatInt64_X	.NET 7.0	-9223372036854775808	19.803 ns	0.4241 ns	0.6082 ns	1.00	294 B
TryFormatInt64_Default	main	123	10.610 ns	0.1336 ns	0.1250 ns	1.62	974 B
TryFormatInt64_Default	pr	123	8.754 ns	0.1467 ns	0.1225 ns	1.34	1,167 B
TryFormatInt64_Default	.NET 7.0	123	6.558 ns	0.1536 ns	0.1508 ns	1.00	829 B
TryFormatUInt64_Default	main	12345	10.376 ns	0.2275 ns	0.2337 ns	1.41	608 B
TryFormatUInt64_Default	pr	12345	5.027 ns	0.0532 ns	0.0498 ns	0.68	318 B
TryFormatUInt64_Default	.NET 7.0	12345	7.379 ns	0.0931 ns	0.0825 ns	1.00	458 B
TryFormatInt32_Default	main	42	9.973 ns	0.0832 ns	0.0737 ns	1.78	964 B
TryFormatInt32_Default	pr	42	2.933 ns	0.0472 ns	0.0442 ns	0.52	348 B
TryFormatInt32_Default	.NET 7.0	42	5.609 ns	0.0647 ns	0.0574 ns	1.00	829 B
TryFormatInt32_D2	main	42	20.623 ns	0.1623 ns	0.1518 ns	3.26	2,438 B
TryFormatInt32_D2	pr	42	4.125 ns	0.1098 ns	0.0917 ns	0.65	573 B
TryFormatInt32_D2	.NET 7.0	42	6.340 ns	0.0438 ns	0.0366 ns	1.00	581 B
TryFormatUInt64_X4	main	4660	21.726 ns	0.4386 ns	0.3662 ns	3.69	2,030 B
TryFormatUInt64_X4	pr	4660	6.411 ns	0.0568 ns	0.0474 ns	1.09	257 B
TryFormatUInt64_X4	.NET 7.0	4660	5.841 ns	0.1648 ns	0.1897 ns	1.00	290 B

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

[DrewScoggins]

Still seeing a regression in this test https://pvscmdupload.blob.core.windows.net/reports/allTestHistory/refs/heads/main_x64_ubuntu%2018.04/System.Buffers.Text.Tests.Utf8FormatterTests.FormatterDecimal(value%3a%20123456.789).html

Found during 7.0 -> 8.0 perf comparison.