Optimize "(vec & cns) == zero" on arm64

[EgorBo]

Fixes #100922 regression - it was regressed by #99982

bool AllAscii(Vector128<byte> vector) => 
    (vector & Vector128.Create((byte)0x80)).Equals(Vector128<byte>.Zero);

Main:

; Method Proga:AllAscii
            stp     fp, lr, [sp, #-0x10]!
            mov     fp, sp
            movi    v16.16b, #0x80
            and     v16.16b, v0.16b, v16.16b
            umaxp   v16.4s, v16.4s, v16.4s
            umov    x0, v16.d[0]
            cmp     x0, #0
            cset    x0, eq
            ldp     fp, lr, [sp], #0x10
            ret     lr
; Total bytes of code: 40

PR:

; Method Proga:AllAscii
            stp     fp, lr, [sp, #-0x10]!
            mov     fp, sp
            umaxp   v16.4s, v0.4s, v0.4s
            umov    x0, v16.d[0]
            tst     x0, #0x8080808080808080
            cset    x0, eq
            ldp     fp, lr, [sp], #0x10
            ret     lr
; Total bytes of code: 32

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[EgorBo]

@EgorBot -arm64 -profiler

using BenchmarkDotNet.Attributes;
using System.Buffers;
using System.Text;
using BenchmarkDotNet.Running;

BenchmarkRunner.Run<Perf_Ascii>(args: args);

[DisassemblyDiagnoser(maxDepth: 5)]
public class Perf_Ascii
{
    byte[] _bytes = new byte[128];
    char[] _characters = new char[128];

    [Benchmark]
    public OperationStatus ToUtf16() => Ascii.ToUtf16(_bytes, _characters, out _);
}

[EgorBot]

Results on Arm64

BenchmarkDotNet v0.13.12, Ubuntu 22.04.4 LTS (Jammy Jellyfish)
Unknown processor
  Job-TOHLVW : .NET 9.0.0 (42.42.42.42424), Arm64 RyuJIT AdvSIMD
  Job-IXPJBK : .NET 9.0.0 (), Arm64 RyuJIT AdvSIMD

Method	Toolchain	Mean	Error	Ratio	Code Size
ToUtf16	Main	17.24 ns	0.004 ns	1.00	516 B
ToUtf16	PR	15.67 ns	0.001 ns	0.91	500 B

See BDN_Artifacts.zip for details.

🔥Profiler

Flame graphs: Main vs PR (interactive!)
Hot asm: Main vs PR
Hot functions: Main vs PR

Notes

For clean perf results, make sure you have just one [Benchmark] in your app.

[tannergooding]

This doesn't have to be a constant right?

Just any (x & y) == zero or (x & y) != zero can be optimzied down to a tst (on both xarch and arm64).

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Draft Pull Request was automatically closed for 30 days of inactivity. Please let us know if you'd like to reopen it.

[xtqqczze]

Blocks #105047.

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Draft Pull Request was automatically closed for 30 days of inactivity. Please let us know if you'd like to reopen it.