Spooky allocations - linked to Varargs?

General Usage Performance
2

Interesting.

If I do a

f(x...) = multinomial(x...)
@code_native f(1,2,3,4,5)

There’s a sequence:

        movabs  rbx, offset ijl_box_int64
        lea     rdx, [rbp - 112]
        mov     r12, rsi
        mov     rcx, qword ptr [rax - 8]
        mov     qword ptr [rbp - 112], 20
        mov     rax, qword ptr [rcx]
        mov     qword ptr [rbp - 56], rcx       # 8-byte Spill
        mov     qword ptr [rbp - 104], rax
        mov     qword ptr [rcx], rdx
        vzeroupper
        call    rbx

So it seems something is being boxed. It’s likely something with the Vararg.

Incidentally, I see the same boxing with:

@noinline f(x...) = (s = 0; for i in x; s += i; end; s)
g(x...) = f(x...)
@code_native g(1,2,3)

though I do not get any allocations with @btime g(1,2,3)

I get this odd thing:

julia> @code_typed g(1,2,3)
CodeInfo(
1 ─ %1 = Core.getfield(x, 1)::Int64
│   %2 = Core.getfield(x, 2)::Int64
│   %3 = Core.getfield(x, 3)::Int64
│   %4 = invoke Main.f(%1::Int64, %2::Vararg{Int64}, %3)::Int64
└──      return %4
) => Int64

(v1.11.1)