filter.jl

function vfilter!(
  f::F,
  x::Vector{T},
  y::AbstractArray{T}
) where {F,T<:NativeTypes}
  W, Wshift = VectorizationBase.pick_vector_width_shift(T)
  N = length(y)
  Nrep = N >>> Wshift
  Nrem = N & (W - 1)
  j = 0
  st = VectorizationBase.static_sizeof(T)
  zero_index = MM(W, StaticInt(0), st)
  incr = W * VectorizationBase.static_sizeof(T)
  GC.@preserve x y begin
    # ptr_x = llvmptr(x); ptr_y = llvmptr(y)
    ptr_x = pointer(x)
    ptr_y = pointer(y)
    for _ ∈ 1:Nrep
      vy =
        VectorizationBase.__vload(ptr_y, zero_index, False(), register_size())
      mask = f(vy)
      VectorizationBase.compressstore!(
        gep(ptr_x, VectorizationBase.lazymul(st, j)),
        vy,
        mask
      )
      ptr_y = gep(ptr_y, incr)
      j = vadd_nw(j, count_ones(mask))
    end
    rem_mask = VectorizationBase.mask(T, Nrem)
    vy = VectorizationBase.__vload(
      ptr_y,
      zero_index,
      rem_mask,
      False(),
      register_size()
    )
    mask = rem_mask & f(vy)
    VectorizationBase.compressstore!(
      gep(ptr_x, VectorizationBase.lazymul(st, j)),
      vy,
      mask
    )
    j = vadd_nw(j, count_ones(mask))
    Base._deleteend!(x, N - j) # resize!(x, j)
  end
  x
end
vfilter!(f::F, x::Vector{T}) where {F,T<:NativeTypes} = vfilter!(f, x, x)
vfilter(f::F, y::AbstractArray{T}) where {F,T<:NativeTypes} =
  vfilter!(f, Vector{T}(undef, length(y)), y)
vfilter(f::F, y) where {F} = filter(f, y)
vfilter!(f::F, y) where {F} = filter!(f, y)

"""
    vfilter(f, a::AbstractArray)

SIMD-vectorized `filter`, returning an array containing the elements of `a` for which `f` return `true`.

This function requires AVX512 to be faster than `Base.filter`, as it adds compressstore instructions.
"""
vfilter

"""
    vfilter!(f, a::AbstractArray)

SIMD-vectorized `filter!`, removing the element of `a` for which `f` is false.
"""
vfilter!