Improve codegen for delegate cast / type check? #55841
Description
Consider:
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;
using System.Runtime.CompilerServices;
[DisassemblyDiagnoser]
[MemoryDiagnoser]
public class Program
{
public static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);
private object _o = (Action)(() => { });
[Benchmark] public void Cast() => M1(_o);
[Benchmark] public void TypeCheck() => M2(_o);
private void M1(object o)
{
if (o is Action action)
action();
}
private void M2(object o)
{
if (o is not null && o.GetType() == typeof(Action))
Unsafe.As<Action>(o)();
}
}On my machine, this results in:
| Method | Mean | Error | StdDev | Gen 0 | Gen 1 | Gen 2 | Allocated | Code Size |
|---|---|---|---|---|---|---|---|---|
| Cast | 1.1969 ns | 0.0083 ns | 0.0078 ns | - | - | - | - | 43 B |
| TypeCheck | 0.7173 ns | 0.0064 ns | 0.0060 ns | - | - | - | - | 36 B |
with the disassembly:
.NET 6.0.0 (42.42.42.42424), X64 RyuJIT
; Program.Cast()
mov rax,[rcx+8]
test rax,rax
je short M00_L00
mov rcx,offset MT_System.Action
cmp [rax],rcx
je short M00_L00
xor eax,eax
M00_L00:
test rax,rax
je short M00_L01
mov rcx,[rax+8]
mov rax,[rax+18]
jmp rax
M00_L01:
ret
; Total bytes of code 43.NET 6.0.0 (42.42.42.42424), X64 RyuJIT
; Program.TypeCheck()
mov rax,[rcx+8]
test rax,rax
je short M00_L00
mov rcx,offset MT_System.Action
cmp [rax],rcx
jne short M00_L00
mov rcx,[rax+8]
mov rax,[rax+18]
jmp rax
M00_L00:
ret
; Total bytes of code 36Is there anything we could do to eliminate the (small) gap / extra branch?