benchmark.fs

open BenchmarkDotNet.Attributes
open BenchmarkDotNet.Configs
open BenchmarkDotNet.Environments
open BenchmarkDotNet.Jobs
open BenchmarkDotNet.Running

[<MemoryDiagnoser(displayGenColumns=false)>]
[<HideColumns("Job", "Error", "StdDev", "Median", "RatioSD")>]
type Benchmarks () =
    let x = Some 3

    [<Benchmark>]
    member _.DoSomeStuffWithOptions () =
        x
        |> Option.map ((+) 1)    // Used to allocate on the heap, now it doesn't.
        |> Option.map ((+) -1)   // Used to allocate on the heap, now it doesn't.
        |> Option.defaultValue 0

ignore <| BenchmarkRunner.Run<Benchmarks>
    (DefaultConfig.Instance
        .AddJob(Job.Default.AsBaseline().WithRuntime CoreRuntime.Core80)
        .AddJob(Job.Default.WithRuntime CoreRuntime.Core90))

gistfile1.txt

| Method                 | Runtime  | Mean      | Ratio | Allocated | Alloc Ratio |
|----------------------- |--------- |----------:|------:|----------:|------------:|
| DoSomeStuffWithOptions | .NET 8.0 | 3.8792 ns |  1.00 |      48 B |        1.00 |
| DoSomeStuffWithOptions | .NET 9.0 | 0.6274 ns |  0.16 |         - |        0.00 |

Yeah, "side-effects" of inlining will oftentimes result in allocations being also inlined as opposed to being in their own functions. Like it happened to be the case for the Option module. We might wanna see how things are inlining in certain CEs or maybe Asyncs (I suspect it's not gonna be inlining too much).