extension CircularBuffer {
    @inline(never)
    func F() {
        _ = first!     // << this allocates as it calls generic specialization <repro.NIOAny> of repro.CircularBuffer.subscript.read : (repro.CircularBuffer<A>.Index) -> A
    }
}
protocol p {
    init()
}
struct CircularBuffer<d: p>{
    var e: ContiguousArray<d?> = [.init()]
    struct Index: Comparable {
        var f: Int = 0
        var i: Int {
            return f
        }
        static func == (a: Index, j: Index) -> Bool {
                return a.i > j.i
        }
        static func < (aa: Index, j: Index) -> Bool {
                return aa.i < j.i
        }
    }
    func index(after: Index) -> Index {
        return index(after, offsetBy: 1)
    }
    subscript(k: Index) -> d {
        get {
            return e[k.i]!
        }
    }
    var startIndex = Index()
    var endIndex = Index()
}
extension CircularBuffer: Collection {}

enum XY {
    case X
    case Y
}

struct NIOAny: p {
    let av: aw = .ay(())
    enum aw {
        case ax(XY)
        case ay(Any)
        init<az>(a: az) {
            self = .ay(a)
        }
    }
}

let b = CircularBuffer<NIOAny>()
for _ in 0..<10000 {
    b.F()
}

                       _$s5repro14CircularBufferVyxAC5IndexVyx_GcirAA6NIOAnyV_Tg5:        // generic specialization <repro.NIOAny> of repro.CircularBuffer.subscript.read : (repro.CircularBuffer<A>.Index) -> A
0x0000000100002110         push       rbp                                       ; CODE XREF=_$s5repro14CircularBufferV1FyyFAA6NIOAnyV_Tg5+34
0x0000000100002111         mov        rbp, rsp
0x0000000100002114         push       r15
0x0000000100002116         push       r14
0x0000000100002118         push       r12
0x000000010000211a         push       rbx
0x000000010000211b         sub        rsp, 0x30
0x000000010000211f         mov        r14, rdx
0x0000000100002122         mov        r15, rsi
0x0000000100002125         mov        r12, rdi
0x0000000100002128         mov        edi, 0x21                                 ; argument "size" for method imp___stubs__malloc
0x000000010000212d         call       imp___stubs__malloc                       ; malloc

$ swiftc -O ~/tmp/repro.swift && sudo ~/devel/swift-nio/dev/malloc-aggregation.d -c ./repro
dtrace: system integrity protection is on, some features will not be available


=====
This will collect stack shots of allocations and print it when you exit dtrace.
So go ahead, run your tests and then press Ctrl+C in this window to see the aggregated result
=====
[...]

              libsystem_malloc.dylib`malloc
              repro`specialized CircularBuffer.subscript.read+0x22
              repro`specialized CircularBuffer.F()+0x27
              repro`main+0x7c
              libdyld.dylib`start+0x1
              0x1
            10000

Swift version 5.4-dev (LLVM 7a20f40c45aca5d, Swift 031b848b7092c06)

#!/bin/bash

set -eu

swiftc -O repro.swift
objdump -d repro |  grep -A14 '14CircularBufferVyxAC5IndexVyx_GcirAA6NIOAnyV_Tg5>:' | grep -q malloc