Hi,

I’m trying to optimize my code and I noticed a type instability when using broadcasting together with the splat operator, as in the following code:

```
function f(x, p1, p2)
return x * p1 + p2
end
x = rand(1000)
p1 = 2.0
p2 = 3.0
p0 = [p1, p2]
f.(x, p0...)
@code_warntype f.(x, p0...)
```

and I get the following

```
MethodInstance for (::var"##dotfunction#389#20")(::Vector{Float64}, ::Vector{Float64})
from (::var"##dotfunction#389#20")(x1, x2) @ Main none:0
Arguments
#self#::Core.Const(var"##dotfunction#389#20"())
x1::Vector{Float64}
x2::Vector{Float64}
Body::Any
1 ─ %1 = Core.tuple(Main.f, x1)::Tuple{typeof(f), Vector{Float64}}
│ %2 = Core._apply_iterate(Base.iterate, Base.broadcasted, %1, x2)::Any
│ %3 = Base.materialize(%2)::Any
└── return %3
```

On the contrary, if I insert the elements individually, everything is fine.

I would prefer to use the splat operator since I have a lot of parameters to insert.