JIT: Inline static readonly delegates

[EgorBo]

static Func<int, int, int> MyFunc { get; } = (x, y) => x + y;

static int Test() => RunFunc(MyFunc);

static int RunFunc(Func<int, int, int> processor)
{
    return processor(10, 20);
}

codegen for Test() with PGO enabled:

       mov      eax, 30
       ret      
; Total bytes of code 6

Not sure it's super useful (how often developers save delegates to static readonly?) but it's the first case when we can inline a lambda without checks 🙂

UPD: Also, it seems to fold typeof(T).TypeHandle.Value; and closes #5973

static nint Test()
{
    return typeof(int).TypeHandle.Value;
}

codegen:

       mov      rax, 0x7FF7A3C3EA58
       ret 
; Total bytes of code 11

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Issue Details

---

static Func<int, int, int> MyFunc { get; } = (x, y) => x + y;

static int Test() => RunFunc(MyFunc);

static int RunFunc(Func<int, int, int> processor)
{
    return processor(10, 20);
}

codegen for Test() with PGO enabled:

; Assembly listing for method Program:Foo():int
; Tier-1 compilation
       mov      eax, 30
       ret      
; Total bytes of code 6

Not sure it's super useful (how often developers save delegates to static readonly?) but it's a first case when we can inline a lambda without checks 🙂

Author:	EgorBo
Assignees:	EgorBo
Labels:	area-CodeGen-coreclr
Milestone:	-

[stephentoub]

how often developers save delegates to static readonly

This is quite common. However it's much less common to invoke the delegate directly from that field... the primary use is passing it off to another method that will then invoke it, and that method is often not going to be inlined.

[EgorBo]

how often developers save delegates to static readonly

This is quite common. However it's much less common to invoke the delegate directly from that field... the primary use is passing it off to another method that will then invoke it, and that method is often not going to be inlined.

Ah so do we need this? 🙂 The PR should be fully complete, it's just that it's +100 LOC and needs tests, I extracted TypeHandle part into a separate PR

[stephentoub]

Ah so do we need this?

My gut is it won't help much. But if there's an easy way to see how often it would kick in across runtime, for example, I'd be happy to be proven wrong.

[omariom]

I need both of the changes. Thanks!

[stephentoub]

I need both of the changes

Can you comment on where on hot paths you directly invoke delegates stored in static readonly fields? Thanks.

[omariom]

It was the case I was loading and compiling simple text expressions into delegates, which were then used directly as filters and calculated fields, or in implementations of other filters.
I understand that interface and virtual dispatch are now inlinable when accessed via static readonlies, and I could use them,
but it would be nice if all the dynamic dispatches behaved uniformly in this sense.

[EgorBo]

@omariom we might get this behavior for free and for other lambdas if we land #85014 and Roslyn will start emitting it for lambdas