Trim some overheads for "r"/"o" DateTime parsing

[stephentoub]

We were doing some unnecessary work on these fast paths:

• We were calling ConfigureFormatR/O even though the work they were doing was never used. Removed the calls and then inlined the code into the remaining call sites.
• Removed unnecessary arguments.
• Removed a virtual dispatch calling to GregorianCalendar when we could instead just go straight to the helper on DateTime.
• Reduced number of cases in switch statement.
• I also noticed and cleaned up an unnecessary delegate involved in Hebrew number parsing.

private string _r = new DateTime(1955, 11, 5, 6, 0, 0, DateTimeKind.Utc).ToString("r", CultureInfo.InvariantCulture);
private string _o = new DateTime(1955, 11, 5, 6, 0, 0, DateTimeKind.Utc).ToString("o", CultureInfo.InvariantCulture);

[Benchmark] public DateTimeOffset ParseR() => DateTimeOffset.ParseExact(_r, "r", CultureInfo.InvariantCulture);
[Benchmark] public DateTimeOffset ParseO() => DateTimeOffset.ParseExact(_o, "o", CultureInfo.InvariantCulture);

Method	Toolchain	Mean	Error	StdDev	Ratio
ParseR	\main\corerun.exe	42.55 ns	0.552 ns	0.636 ns	1.00
ParseR	\pr\corerun.exe	38.56 ns	0.556 ns	0.520 ns	0.91
ParseO	\main\corerun.exe	49.60 ns	0.501 ns	0.468 ns	1.00
ParseO	\pr\corerun.exe	43.75 ns	0.402 ns	0.376 ns	0.88

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Issue Details

---

We were doing some unnecessary work on these fast paths:

• We were calling ConfigureFormatR/O even though the work they were doing was never used. Removed the calls and then inlined the code into the remaining call sites.
• Removed unnecessary arguments.
• Removed a virtual dispatch calling to GregorianCalendar when we could instead just go straight to the helper on DateTime.
• Reduced number of cases in switch statement.
• I also noticed and cleaned up an unnecessary delegate involved in Hebrew number parsing.

private string _r = new DateTime(1955, 11, 5, 6, 0, 0, DateTimeKind.Utc).ToString("r", CultureInfo.InvariantCulture);
private string _o = new DateTime(1955, 11, 5, 6, 0, 0, DateTimeKind.Utc).ToString("o", CultureInfo.InvariantCulture);

[Benchmark] public DateTimeOffset ParseR() => DateTimeOffset.ParseExact(_r, "r", CultureInfo.InvariantCulture);
[Benchmark] public DateTimeOffset ParseO() => DateTimeOffset.ParseExact(_o, "o", CultureInfo.InvariantCulture);

Method	Toolchain	Mean	Error	StdDev	Ratio
ParseR	\main\corerun.exe	42.55 ns	0.552 ns	0.636 ns	1.00
ParseR	\pr\corerun.exe	38.56 ns	0.556 ns	0.520 ns	0.91
ParseO	\main\corerun.exe	49.60 ns	0.501 ns	0.468 ns	1.00
ParseO	\pr\corerun.exe	43.75 ns	0.402 ns	0.376 ns	0.88

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.Globalization
Milestone:	-

[tarekgh]

LGTM

[stephentoub]

Thanks

[EgorBo]

Improvements on ubuntu-arm64:

• [Perf] Linux/arm64: 2 Improvements on 3/4/2023 1:07:20 AM perf-autofiling-issues#13825