Delegates are not being inlined

[hez2010]

Description

Repro:

[MethodImpl(MethodImplOptions.NoInlining)]
static int M()
{
    var x = F(5);
    return x();
}

static Func<int> F(int x)
{
    return () => 5 + x;
}

JIT dump for M (Tier1):

push    rbp
mov     rbp,rsp
mov     edi,5
call    <Program>$.<<Main>$>g__F|0_1(Int32)
mov     rsi,rax
mov     rdi,offset methodtable(System.Func`1[[System.Int32, System.Private.CoreLib]])
call    CORINFO_HELP_CHKCASTARRAY
mov     rdi,[rax+8]
call    qword ptr [rax+18h]
nop
pop     rbp
ret

If I have AggressiveInlining on F:

push    rbp
push    r14
push    rbx
lea     rbp,[rsp+10h]
mov     rdi,offset methodtable(<Program>$+<>c__DisplayClass0_0)
call    CORINFO_HELP_NEWSFAST
mov     rbx,rax
mov     dword ptr [rbx+8],5
mov     rdi,offset methodtable(System.Func`1[[System.Int32, System.Private.CoreLib]])
call    CORINFO_HELP_NEWSFAST
mov     r14,rax
lea     rdi,[r14+8]
mov     rsi,rbx
call    CORINFO_HELP_ASSIGN_REF
mov     rdi,offset <Program>$+<>c__DisplayClass0_0.<<Main>$>b__13()
mov     [r14+18h],rdi
mov     rdi,[r14+8]
call    qword ptr [r14+18h]
nop
pop     rbx
pop     r14
pop     rbp
ret

Also, I tried creating the delegate without using lambdas:

[MethodImpl(MethodImplOptions.NoInlining)]
static int M()
{
    var x = Foo(5);
    return x();
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
static Func<int> Foo(int x)
{
    var d = new D();
    d.x = x;
    return new Func<int>(d.f);
}

sealed class D
{
    public int x;
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public int f() => 5 + x;
}

It gives codegen:

push    rbp
push    r14
push    rbx
lea     rbp,[rsp+10h]
mov     rdi,offset methodtable(D)
call    CORINFO_HELP_NEWSFAST
mov     rbx,rax
mov     dword ptr [rbx+8],5
mov     rdi,offset methodtable(System.Func`1[[System.Int32, System.Private.CoreLib]])
call    CORINFO_HELP_NEWSFAST
mov     r14,rax
lea     rdi,[r14+8]
mov     rsi,rbx
call    CORINFO_HELP_ASSIGN_REF
mov     rdi,offset D.f()
mov     [r14+18h],rdi
mov     rdi,[r14+8]
call    qword ptr [r14+18h]
nop
pop     rbx
pop     r14
pop     rbp
ret

Expected codegen:

mov     eax, 0xa
ret

Configuration

.NET: 6.0.100-rc.1.21379.19

[davidfowl]

Delegates are never inlined #44610

[JulieLeeMSFT]

@hez2010 Is it ok to close this issue because it is answered by davidfowl?

[hez2010]

@hez2010 Is it ok to close this issue because it is answered by davidfowl?

Sure. I'm closing this issue.