Expand unboxing for Nullable<> in JIT #105073

EgorBo · 2024-07-18T09:39:36Z

Currently, unboxing for Nullable<> always go through a helper call, while we can inline it in JIT.

int? Test(object o) => (int?)o;

Current codegen:

; Method Proga:Test(System.Object):System.Nullable`1[int]:this (FullOpts)
G_M11066_IG01:
       sub      rsp, 40
G_M11066_IG02:
       lea      rcx, [rsp+0x20]
       mov      r8, rdx
       mov      rdx, 0x7FF7E261B750      ; System.Nullable`1[int]
       call     CORINFO_HELP_UNBOX_NULLABLE
       mov      rax, qword ptr [rsp+0x20]
G_M11066_IG03:
       add      rsp, 40
       ret      
; Total bytes of code: 37

New codegen:

; Method Proga:Test(System.Object):System.Nullable`1[int]:this (FullOpts)
G_M11066_IG01:
       sub      rsp, 40
G_M11066_IG02:
       test     rdx, rdx ;; is null?
       je       SHORT G_M11066_IG04
G_M11066_IG03:
       mov      rax, 0x7FF7E23674D0      ; System.Int32
       cmp      qword ptr [rdx], rax ;; is object's type int32?
       je       SHORT G_M11066_IG05
       jmp      SHORT G_M11066_IG08
G_M11066_IG04:
       xor      edx, edx
       mov      qword ptr [rsp+0x20], rdx
       jmp      SHORT G_M11066_IG06
G_M11066_IG05:
       mov      byte  ptr [rsp+0x20], 1
       mov      eax, dword ptr [rdx+0x08]
       mov      dword ptr [rsp+0x24], eax
G_M11066_IG06:
       mov      rax, qword ptr [rsp+0x20]
G_M11066_IG07:
       add      rsp, 40
       ret      

; cold path
G_M11066_IG08:
       lea      rcx, [rsp+0x20]
       mov      r8, rdx
       mov      rdx, 0x7FF7E263B750      ; System.Nullable`1[int]
       call     CORINFO_HELP_UNBOX_NULLABLE
       jmp      SHORT G_M11066_IG06
; Total bytes of code: 82

Benchmark:

using BenchmarkDotNet.Attributes;

public class MyBench
{
    [Benchmark]
    [Arguments(42)]
    [Arguments(null)]
    public int? Unbox(object o) => (int?)o;
}

BenchmarkDotNet v0.13.12, Ubuntu 22.04.4 LTS (Jammy Jellyfish)
Unknown processor (which is "Ampere Altra")
  Job-MMNLPR : .NET 9.0.0 (42.42.42.42424), Arm64 RyuJIT AdvSIMD
  Job-QXOQTU : .NET 9.0.0 (42.42.42.42424), Arm64 RyuJIT AdvSIMD

Method	Toolchain	o	Mean	Error	Ratio
Unbox	Main	?	7.1195 ns	0.0098 ns	1.00
Unbox	PR	?	0.6698 ns	0.0072 ns	0.09

Unbox	Main	42	10.9406 ns	0.0175 ns	1.00
Unbox	PR	42	2.7002 ns	0.0001 ns	0.25

EgorBo · 2024-07-18T09:42:12Z

@EgorBot -intel -arm64

using BenchmarkDotNet.Attributes;

public class MyBench
{
    [Benchmark]
    [Arguments(42)]
    [Arguments(null)]
    public int? Unbox(object o) => (int?)o;
}

huoyaoyuan · 2024-07-18T09:47:42Z

Does it worth to recognize RuntimeHelpers.Unbox_Nullable and do the same expansion?

Or, can we write the method in C# and make helpers inlinable? This will help more around nullables.

EgorBo · 2024-07-18T09:54:27Z

Or, can we write the method in C# and make helpers inlinable? This will help more around nullables.

Yes, that is an option, requires some effort to make helpers inlineable, they're currently not. I decided to do it in JIT since the actual change is like 30 LOC, the rest are comments. If we move it to an inlineable helper we can delete this I guess..
I'll take a look at that next week probably.

EgorBot · 2024-07-18T10:01:23Z

Benchmark results on Intel

BenchmarkDotNet v0.13.12, Ubuntu 22.04.4 LTS (Jammy Jellyfish)
Intel Xeon Platinum 8370C CPU 2.80GHz, 1 CPU, 8 logical and 4 physical cores
  Job-XHSURK : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  Job-ZDCIDK : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI

Method	Toolchain	o	Mean	Error	Ratio
Unbox	Main	?	4.4659 ns	0.0093 ns	1.00
Unbox	PR	?	0.5740 ns	0.0003 ns	0.13

Unbox	Main	42	7.1867 ns	0.0395 ns	1.00
Unbox	PR	42	3.9114 ns	0.0016 ns	0.54

BDN_Artifacts.zip

EgorBot · 2024-07-18T10:14:24Z

Benchmark results on Arm64

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

Method	Toolchain	o	Mean	Error	Ratio
Unbox	Main	?	7.1195 ns	0.0098 ns	1.00
Unbox	PR	?	0.6698 ns	0.0072 ns	0.09

Unbox	Main	42	10.9406 ns	0.0175 ns	1.00
Unbox	PR	42	2.7002 ns	0.0001 ns	0.25

BDN_Artifacts.zip

EgorBo · 2024-07-18T10:32:39Z

@MihuBot

EgorBo · 2024-07-18T12:27:59Z

@jakobbotsch @AndyAyersMS cc @dotnet/jit-contrib PTAL, the actual change is 40 LOC, benchmarks attached. Jit-diff: MihuBot/runtime-utils#541 obviously, a size regression, but there were also a few cases where jit can now fold the if we emit here, e.g. previously we never tried to fold CORINFO_HELP_UNBOX_NULLABLE(null) etc.

EgorBo · 2024-07-18T12:29:48Z

src/coreclr/jit/importer.cpp

+    // Unbox the object to the result local:
+    //
+    //  result._hasValue = true;
+    //  result._value = MethodTableLookup(obj);


oops, wrong comment, it's obj->RawData

AndyAyersMS

Would it be worth limiting this to relatively small types, since will create both a zeroing and a copy?

EgorBo · 2024-07-18T18:01:28Z

Might be a good idea to limit it, yeah

@EgorBot -intel -arm64

using System.Runtime.CompilerServices;
using BenchmarkDotNet.Attributes;

public class MyBench2
{
    [InlineArray(100)]
    public struct LargeStruct
    {
        public long Fld;
    }

    [Benchmark]
    [Arguments(42)]
    [Arguments(null)]
    public LargeStruct? Unbox(object o) => (LargeStruct?)o;
}

EgorBot · 2024-07-18T18:19:39Z

Benchmark results on Intel

BenchmarkDotNet v0.13.12, Ubuntu 22.04.4 LTS (Jammy Jellyfish)
Intel Xeon Platinum 8370C CPU 2.80GHz, 1 CPU, 8 logical and 4 physical cores
  Job-BUSFSY : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  Job-NIMINM : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI

Method	Toolchain	o	Mean	Error	Ratio
Unbox	Main	?	27.91 ns	0.013 ns	1.00
Unbox	PR	?	20.32 ns	0.010 ns	0.73

Unbox	Main	42	NA	NA	?
Unbox	PR	42	NA	NA	?
Benchmarks with issues:
MyBench2.Unbox: Job-BUSFSY(Toolchain=Main) [o=42]
MyBench2.Unbox: Job-NIMINM(Toolchain=PR) [o=42]

BDN_Artifacts.zip

EgorBo · 2024-07-18T18:21:58Z

@EgorBot -intel -arm64

using System.Runtime.CompilerServices;
using BenchmarkDotNet.Attributes;

public class MyBench2
{
    [InlineArray(100)]
    public struct LargeStruct
    {
        public long Fld;
    }

    public IEnumerable<object> TestData()
    {
        yield return null;
        yield return new LargeStruct();
    }

    [Benchmark]
    [ArgumentsSource(nameof(TestData))]
    public LargeStruct? Unbox(object o) => (LargeStruct?)o;
}

EgorBot · 2024-07-18T18:41:04Z

Benchmark results on Intel

BenchmarkDotNet v0.13.12, Ubuntu 22.04.4 LTS (Jammy Jellyfish)
Intel Xeon Platinum 8370C CPU 2.80GHz, 1 CPU, 8 logical and 4 physical cores
  Job-GNOQYR : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  Job-LOMSQK : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI

Method	Toolchain	o	Mean	Error	Ratio
Unbox	Main	?	31.62 ns	0.038 ns	1.00
Unbox	PR	?	21.39 ns	0.013 ns	0.68

Unbox	Main	MyBench2+LargeStruct	29.85 ns	0.010 ns	1.00
Unbox	PR	MyBench2+LargeStruct	26.19 ns	0.005 ns	0.88

BDN_Artifacts.zip

EgorBot · 2024-07-18T18:53:44Z

Benchmark results on Arm64

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

Method	Toolchain	o	Mean	Error	Ratio
Unbox	Main	?	89.28 ns	0.041 ns	1.00
Unbox	PR	?	39.46 ns	0.023 ns	0.44

Unbox	Main	MyBench2+LargeStruct	48.70 ns	0.052 ns	1.00
Unbox	PR	MyBench2+LargeStruct	41.85 ns	0.209 ns	0.86

BDN_Artifacts.zip

EgorBo added 2 commits July 18, 2024 11:18

Expand nullable unbox in JIT

99fb623

reorder blocks

49aca95

dotnet-issue-labeler bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jul 18, 2024

dotnet-policy-service bot assigned EgorBo Jul 18, 2024

MihuBot mentioned this pull request Jul 18, 2024

[JitDiff X64] [EgorBo] Expand unboxing for Nullable<> in JIT MihuBot/runtime-utils#540

Open

Only with optimizations and in hot blocks

9ef585b

MihuBot mentioned this pull request Jul 18, 2024

[JitDiff X64] [EgorBo] Expand unboxing for Nullable<> in JIT MihuBot/runtime-utils#541

Open

EgorBo marked this pull request as ready for review July 18, 2024 10:32

EgorBo requested review from jakobbotsch and AndyAyersMS July 18, 2024 12:28

EgorBo commented Jul 18, 2024

View reviewed changes

build-analysis bot mentioned this pull request Jul 18, 2024

Assertion failed (pThread->m_StateNC & Thread::TSNC_OwnsSpinLock) == 0 #104449

Closed

AndyAyersMS approved these changes Jul 18, 2024

View reviewed changes

dotnet deleted a comment from EgorBot Jul 18, 2024

EgorBo added 2 commits July 19, 2024 00:55

clean up, address feedback

2918411

Merge branch 'main' into nullable-expand

a3cb9d2

Update importer.cpp

d5c1948

EgorBo merged commit f8bcd05 into dotnet:main Jul 19, 2024
101 of 108 checks passed

EgorBo deleted the nullable-expand branch July 19, 2024 12:20

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Expand unboxing for Nullable<> in JIT #105073

Expand unboxing for Nullable<> in JIT #105073

EgorBo commented Jul 18, 2024 •

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Expand unboxing for Nullable<> in JIT #105073

Expand unboxing for Nullable<> in JIT #105073

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EgorBo commented Jul 18, 2024 • edited Loading

Current codegen:

New codegen:

Benchmark:

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