JIT does not recognize typeof(X) == o.GetType() checks as intrinsics with R2R

[jkotas]

Repro:

using System;
using System.Runtime.CompilerServices;

public sealed class Test96876
{
    public static void Main()
    {
        foo<Test96876>(new DateTime[1]);
    }

    // Validate that the type equality involving shared array types is handled correctly
    // in shared generic code.
    [MethodImpl(MethodImplOptions.NoInlining)]
    static bool foo<T>(DateTime[] list) => typeof(T[]) == list.GetType();
}

Actual result:

foo<__Canon> is optimized to return constant for JIT, but does full type check for R2R.

Expected result

foo<__Canon> is optimized to return constant for both JIT and R2R.

Optimized JIT code:

G_M10478_IG02:  ;; offset=0x0000
       cmp      byte  ptr [rdx], dl
       xor      eax, eax
                                                ;; size=4 bbWeight=1 PerfScore 3.25
G_M10478_IG03:  ;; offset=0x0004
       ret

Optimized R2R code:

G_M000_IG01:                ;; offset=0x0000
       push     rbx
       sub      rsp, 48
       mov      qword ptr [rsp+0x28], rcx
       mov      rbx, rdx

G_M000_IG02:                ;; offset=0x000D
       call     [CORINFO_HELP_READYTORUN_GENERIC_HANDLE]
       cmp      qword ptr [rbx], rax
       sete     al
       movzx    rax, al

G_M000_IG03:                ;; offset=0x001C
       add      rsp, 48
       pop      rbx
       ret

[ghost]

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Issue Details

---

Repro:

!!!

Actual result:

foo<__Canon> is optimized to return constant for JIT, but does full type check for R2R.

Expected result

foo<__Canon> is optimized to return constant for both JIT and R2R.

Optimized JIT code:

G_M10478_IG02:  ;; offset=0x0000
       cmp      byte  ptr [rdx], dl
       xor      eax, eax
                                                ;; size=4 bbWeight=1 PerfScore 3.25
G_M10478_IG03:  ;; offset=0x0004
       ret

Optimized R2R code:

G_M000_IG01:                ;; offset=0x0000
       push     rbx
       sub      rsp, 48
       mov      qword ptr [rsp+0x28], rcx
       mov      rbx, rdx

G_M000_IG02:                ;; offset=0x000D
       call     [CORINFO_HELP_READYTORUN_GENERIC_HANDLE]
       cmp      qword ptr [rbx], rax
       sete     al
       movzx    rax, al

G_M000_IG03:                ;; offset=0x001C
       add      rsp, 48
       pop      rbx
       ret

Author:	jkotas
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[EgorBo]

Interesting, doesn't repro for me if I set --inputbubble in crossgen.

[EgorBo]

the issue is that impIsClassExact(cls) returns false for DateTime[] class.
looks like getClassAttribs(DateTime[]) returns CORINFO_FLG_VAROBJSIZE | CORINFO_FLG_ARRAY. If I set --inputbubble then it's CORINFO_FLG_FINAL | CORINFO_FLG_ARRAY

that CORINFO_FLG_VAROBJSIZE makes the difference.

[jkotas]

that CORINFO_FLG_VAROBJSIZE makes the difference.

I assume that you meant CORINFO_FLG_FINAL. We may be able to return CORINFO_FLG_FINAL for R2R. However, the larger problem is that impIsClassExact logic is not right. It is hard to synthetize these type properties on the JIT side. The logic has both false positives (functional bugs) and false negatives (perf bugs). Repro for false positive:

C:\>git clone https://github.com/jkotas/EquivalentTypes
Cloning into 'EquivalentTypes'...
remote: Enumerating objects: 17, done.
remote: Counting objects: 100% (17/17), done.
remote: Compressing objects: 100% (14/14), done.
remote: Total 17 (delta 2), reused 17 (delta 2), pack-reused 0
Receiving objects: 100% (17/17), done.
Resolving deltas: 100% (2/2), done.

C:\>cd EquivalentTypes

C:\EquivalentTypes>dotnet publish
MSBuild version 17.8.3+195e7f5a3 for .NET
  Determining projects to restore...
  Restored C:\EquivalentTypes\test.csproj (in 433 ms).
  Restored C:\EquivalentTypes\pia\pia.csproj (in 408 ms).
  Restored C:\EquivalentTypes\mylib\mylib.csproj (in 432 ms).
  pia -> C:\EquivalentTypes\pia\bin\Release\net8.0\pia.dll
  mylib -> C:\EquivalentTypes\mylib\bin\Release\net8.0\mylib.dll
  test -> C:\EquivalentTypes\bin\Release\net8.0\test.dll
  test -> C:\EquivalentTypes\bin\Release\net8.0\publish\

C:\EquivalentTypes>bin\Release\net8.0\publish\test.exe
True

C:\EquivalentTypes>set DOTNET_TieredCompilation=0

C:\EquivalentTypes>bin\Release\net8.0\publish\test.exe
False