Improve getExactClasses to support classes as base types

[MichalStrehovsky]

Fixes #88547

using System.Runtime.CompilerServices;

public class ClassA
{
    public virtual int GetValue() => 42;
}

public class ClassB : ClassA
{
    // we don't even need to override GetValue here
}

class MyClass
{
    static void Main()
    {
        Test(new ClassB());
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    static int Test(ClassA c) => c.GetValue();
}

Old codegen:

; Method MyClass:Test(ClassA):int (FullOpts)
       sub      rsp, 40
       mov      rax, qword ptr [rcx]
       call     [rax+30H]ClassA:GetValue():int:this
       nop
       add      rsp, 40
       ret
; Total bytes of code: 16

New codegen:

00007FF66DD8AFB0  cmp         dword ptr [rcx],ecx
00007FF66DD8AFB2  mov         eax,2Ah
00007FF66DD8AFB7  ret

Cc @dotnet/ilc-contrib @EgorBo

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Issue Details

---

Fixes #88547

using System.Runtime.CompilerServices;

public class ClassA
{
    public virtual int GetValue() => 42;
}

public class ClassB : ClassA
{
    // we don't even need to override GetValue here
}

class MyClass
{
    static void Main()
    {
        Test(new ClassB());
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    static int Test(ClassA c) => c.GetValue();
}

Old codegen:

; Method MyClass:Test(ClassA):int (FullOpts)
       sub      rsp, 40
       mov      rax, qword ptr [rcx]
       call     [rax+30H]ClassA:GetValue():int:this
       nop
       add      rsp, 40
       ret
; Total bytes of code: 16

New codegen:

00007FF66DD8AFB0  cmp         dword ptr [rcx],ecx
00007FF66DD8AFB2  mov         eax,2Ah
00007FF66DD8AFB7  ret

Cc @dotnet/ilc-contrib @EgorBo

Author:	MichalStrehovsky
Assignees:	-
Labels:	area-NativeAOT-coreclr
Milestone:	-

[MichalStrehovsky]

/azp run runtime-nativeaot-outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

Love it! It should also pick up other jit opts like if (obj is Class1) or multiple-guesses GDV, etc which currently only kick in for interfaces. LGTM if CI passes 🙂

[jkotas]

Thanks