Error with ifelse

[jebej]

On LoopVectorization 0.12.9:

using LoopVectorization

function _real_sqrt(x,y)
    t = sqrt(2*(abs(x) + hypot(x, y)))
    return ifelse(x ≥ zero(x), t/2, abs(y)/t)
end

x = (rand(1000).-0.5).*10;
y = (rand(1000).-0.5).*10;

_real_sqrt.(x,y) # works

@avx _real_sqrt.(x,y) # error

The error is:

ERROR: TypeError: non-boolean (VectorizationBase.Mask{4,UInt8}) used in boolean context
Stacktrace:
 [1] _real_sqrt(::VectorizationBase.Vec{4,Float64}, ::VectorizationBase.Vec{4,Float64}) at .\REPL[2]:3
 [2] macro expansion at C:\Users\Jeremy\.julia\packages\LoopVectorization\eSjbW\src\reconstruct_loopset.jl:623 [inlined]
 [3] _avx_! at C:\Users\Jeremy\.julia\packages\LoopVectorization\eSjbW\src\reconstruct_loopset.jl:623 [inlined]
 [4] macro expansion at C:\Users\Jeremy\.julia\packages\LoopVectorization\eSjbW\src\broadcast.jl:393 [inlined]
 [5] vmaterialize! at C:\Users\Jeremy\.julia\packages\LoopVectorization\eSjbW\src\broadcast.jl:393 [inlined]
 [6] vmaterialize(::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1},Nothing,typeof(_real_sqrt),Tuple{Array{Float64,1},Array{Float64,1}}}, ::Val{:Main}, ::Val{(true, 0, 0, true, 0, 32, 15, 64, 32768, 262144, 12582912, 0x0000000000000001)}) at C:\Users\Jeremy\.julia\packages\LoopVectorization\eSjbW\src\broadcast.jl:467
 [7] top-level scope at REPL[6]:1

[chriselrod]

Use IfElse.ifelse.
Base.ifelse is a builtin function, so I can't overload it.

julia> using LoopVectorization, IfElse

julia> function _real_sqrt(x,y)
           t = sqrt(2*(abs(x) + hypot(x, y)))
           return IfElse.ifelse(x ≥ zero(x), t/2, abs(y)/t)
       end
_real_sqrt (generic function with 1 method)

julia> x = (rand(1000).-0.5).*10;

julia> y = (rand(1000).-0.5).*10;

julia> _real_sqrt.(x,y) ≈ @avx _real_sqrt.(x,y)
true

julia> @btime @. $z = _real_sqrt($x, $y);
  9.486 μs (0 allocations: 0 bytes)

julia> @btime @avx @. $z = _real_sqrt($x, $y);
  2.335 μs (0 allocations: 0 bytes)

[chriselrod]

Here is the related issue:
JuliaLang/julia#32844

[chriselrod]

Although I guess this should be solvable via the abstract interpreter. So reopening the issue'd be fine to track that.
That's still a ways away, though.

[jebej]

Thanks!

[chriselrod]

For more of an explanation, vectorization/SIMD means doing multiple operations per instruction. LoopVectorization/VectorizationBase represent that with types like:

julia> using VectorizationBase

julia> vx = Vec(ntuple(_ -> 2rand(), VectorizationBase.pick_vector_width(Float64))...)
Vec{8, Float64}<1.5219234039045744, 1.8300372474242277, 1.5738687191737752, 0.18406707750515228, 0.6740398193024504, 0.253508594387144, 1.715660422824369, 1.6706874133577432>

julia> vx > abs2(vx)
Mask{8,Bit}<0, 0, 0, 1, 1, 1, 0, 0>

This relies on overloading a bunch of functions to make them work as expected.
But unfortunately I can't overload branches (meaning if and ? won't work), and I can't overload builtin functions like ifelse either.