Fast-path in String.Trim

[EgorBo]

Similar to #84210 but for String. I tried to use Span APIs here but there was a small overhead.

Bonus point - "string literal".Trim() is a no-op now, e.g.:

stringTrimLiteral()=>"Hello".Trim();

; Method Program:TrimLiteral():System.String:this
48B9809520802B020000 mov rcx, 0x22B80209580 ;; 'string literal'
- BA03000000 mov edx, 3- FF251BFE0400 tail.jmp [System.String:TrimWhiteSpaceHelper(int):System.String:this]-; Total bytes of code: 21+; Total bytes of code: 11

Since JIT is able to fold if (Length == 0 || (!char.IsWhiteSpace(_firstChar) && !char.IsWhiteSpace(this[^1]))) for a constant string 🙂 e.g. constant folding for RVA[cns]

Benchmarks:

[Benchmark][Arguments("Hello world")][Arguments("Hello world ")][MethodImpl(MethodImplOptions.NoInlining)]publicstringTrim(stringstr)=>str.Trim();[Benchmark]publicstringTrimLiteral()=>"Hello".Trim();

| Method | Toolchain | str | Mean |
|--------------- |---------------------------- |------------- |----------:|
| Trim | \Core_Root\corerun.exe | Hello world | 0.4868 ns |
| Trim | \Core_Root_base\corerun.exe | Hello world | 2.0999 ns |
| | | | |
| Trim | \Core_Root\corerun.exe | Hello world | 7.4285 ns |
| Trim | \Core_Root_base\corerun.exe | Hello world | 6.4529 ns |
| | | | |
| TrimLiteral | \Core_Root\corerun.exe | ? | 0.0086 ns |
| TrimLiteral | \Core_Root_base\corerun.exe | ? | 2.0089 ns |

[EgorBo]

No bound checks here due to #84213

[stephentoub]

Not for this PR, but now that we'll be invoking these helpers only when we know there is something to be trimmed, I wonder whether employing an IndexOfAnyExceptWhitespace would be more useful, i.e. whether there being any whitespace makes it more likely there's enough whitespace for vectorization to be a win.

[ghost]

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Issue Details

---

Similar to #84210 but for String. I tried to use Span APIs here but there was a small overhead.

Bonus point - "string literal".Trim() is a no-op now, e.g.:

stringTrimLiteral()=>"Hello".Trim();

; Method Program:TrimLiteral():System.String:this
48B9809520802B020000 mov rcx, 0x22B80209580 ;; 'string literal'
- BA03000000 mov edx, 3- FF251BFE0400 tail.jmp [System.String:TrimWhiteSpaceHelper(int):System.String:this]-; Total bytes of code: 21+; Total bytes of code: 11

Since JIT is able to fold if (Length == 0 || (!char.IsWhiteSpace(_firstChar) && !char.IsWhiteSpace(this[^1]))) for a constant string 🙂 e.g. constant folding for RVA[cns]

Benchmarks:

[Benchmark][Arguments("Hello world")][Arguments("Hello world ")][MethodImpl(MethodImplOptions.NoInlining)]publicstringTrim(stringstr)=>str.Trim();[Benchmark]publicstringTrimLiteral()=>"Hello".Trim();

| Method | Toolchain | str | Mean |
|--------------- |---------------------------- |------------- |----------:|
| Trim | \Core_Root\corerun.exe | Hello world | 0.4868 ns |
| Trim | \Core_Root_base\corerun.exe | Hello world | 2.0999 ns |
| | | | |
| Trim | \Core_Root\corerun.exe | Hello world | 7.4285 ns |
| Trim | \Core_Root_base\corerun.exe | Hello world | 6.4529 ns |
| | | | |
| TrimLiteral | \Core_Root\corerun.exe | ? | 0.0086 ns |
| TrimLiteral | \Core_Root_base\corerun.exe | ? | 2.0089 ns |

Author:	EgorBo
Assignees:	EgorBo
Labels:	area-System.Runtime
Milestone:	-