Use JIT intrinsic for UTF8 encoding in Utf8.TryWrite's AppendLiteral

[stephentoub]

@EgorBo, the right things don't seem to be happening here, or else I'm misunderstanding how it's supposed to work. I still see a call to ReadUtf8 in the asm.

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Issue Details

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@EgorBo, the right things don't seem to be happening here, or else I'm misunderstanding how it's supposed to work. I still see a call to ReadUtf8 in the asm.

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.Text.Encoding
Milestone:	-

[EgorBo]

@stephentoub do you have a repro? I clonned your branch locally and checked codegen for:

        [MethodImpl(MethodImplOptions.NoInlining)]
        internal static void Egor(ref TryWriteInterpolatedStringHandler h)
        {
            h.AppendLiteral("hello world some long string bla bla bla dewwqedewfwef");
        }

and it looks ok - no ReadUtf8 calls and copying is done using avx2

[stephentoub]

@EgorBo:

private byte[] _buffer = new byte[1000];
private uint _id;

[Benchmark]
public bool TryWrite() => Utf8.TryWrite(_buffer, $"Id: {_id}", out _);

[EgorBo]

@EgorBo:

private byte[] _buffer = new byte[1000];
private uint _id;

[Benchmark]
public bool TryWrite() => Utf8.TryWrite(_buffer, $"Id: {_id}", out _);

Interesting, Checked codegen for TryWrite looks ok:

; Assembly listing for method Program:TryWrite():bool:this (FullOpts)
G_M42047_IG01:  ;; offset=0000H
       push     rdi
       push     rsi
       push     rbx
       sub      rsp, 64
       vxorps   xmm4, xmm4, xmm4
       vmovdqa  xmmword ptr [rsp+20H], xmm4
       vmovdqa  xmmword ptr [rsp+30H], xmm4
       mov      rbx, rcx
G_M42047_IG02:  ;; offset=001AH
       mov      rcx, gword ptr [rbx+08H]
       test     rcx, rcx
       jne      SHORT G_M42047_IG04
G_M42047_IG03:  ;; offset=0023H
       xor      rdx, rdx
       xor      eax, eax
       jmp      SHORT G_M42047_IG05
G_M42047_IG04:  ;; offset=0029H
       lea      rdx, bword ptr [rcx+10H]
       mov      eax, dword ptr [rcx+08H]
G_M42047_IG05:  ;; offset=0030H
       xor      ecx, ecx
       cmp      eax, 4
       setge    cl
       xor      r8, r8
       mov      gword ptr [rsp+20H], r8
G_M42047_IG06:  ;; offset=0040H
       mov      dword ptr [rsp+28H], r8d
       mov      byte  ptr [rsp+2CH], cl
       mov      byte  ptr [rsp+2DH], 0
       mov      bword ptr [rsp+30H], rdx
       mov      dword ptr [rsp+38H], eax
       test     ecx, ecx
       je       SHORT G_M42047_IG12
G_M42047_IG07:  ;; offset=005BH
       mov      ecx, dword ptr [rsp+28H]
       mov      esi, dword ptr [rsp+38H]
       cmp      ecx, esi
       ja       SHORT G_M42047_IG14
       mov      edi, ecx
       add      rdi, bword ptr [rsp+30H]
       sub      esi, ecx
       jns      SHORT G_M42047_IG08
       mov      rdx, 0x1DF80300008      ; ''
       mov      rcx, rdx
       call     [System.Diagnostics.Debug:Fail(System.String,System.String)]
G_M42047_IG08:  ;; offset=0085H
       mov      edx, -1
       cmp      esi, 4
       jl       SHORT G_M42047_IG09
       mov      dword ptr [rdi], 0x203A6449 ;;; <----- "hi: " in utf8
       mov      edx, 4
G_M42047_IG09:  ;; offset=009AH
       test     edx, edx
       jl       SHORT G_M42047_IG10
       add      edx, dword ptr [rsp+28H]
       mov      dword ptr [rsp+28H], edx
       jmp      SHORT G_M42047_IG11
G_M42047_IG10:  ;; offset=00A8H
       mov      byte  ptr [rsp+2CH], 0
       jmp      SHORT G_M42047_IG12
G_M42047_IG11:  ;; offset=00AFH
       mov      edx, dword ptr [rbx+10H]
       lea      rcx, [rsp+20H]
       call     [System.Text.Unicode.Utf8+TryWriteInterpolatedStringHandler:AppendFormatted[uint](uint):bool:this]
G_M42047_IG12:  ;; offset=00BDH
       xor      eax, eax
       cmp      byte  ptr [rsp+2CH], 0
       setne    al
G_M42047_IG13:  ;; offset=00C7H
       add      rsp, 64
       pop      rbx
       pop      rsi
       pop      rdi
       ret      
G_M42047_IG14:  ;; offset=00CFH
       call     [System.ThrowHelper:ThrowArgumentOutOfRangeException()]
       int3     
; Total bytes of code 214

[EgorBo]

Ok, reproduces for me when I run your benchmark in Release using BDN - checking now

[EgorBo]

Interesting, when I run the benchmark with --envvars DOTNET_TieredPGO:0 it works as expected - I no longer see ReadUtf8 call and the result is >2x faster

[EgorBo]

Looks like stale Static PGO problem, --envvars DOTNET_ReadyToRun:0 also helps

[EgorBo]

Ah, stop. There is a general problem with PGO 😢

IsKnownConstant is always false in Tier0 because we never inline - it means that Dynamic PGO reports blocks under IsKnownConstant as always cold, some opts don't kick in for such blocks...

[stephentoub]

I can workaround it here by removing the IsKnownConstant, but that seems like something we need to fix in general for 8 :-)