W3cubDocs

/Julia 0.6

SIMD Support

Type VecElement{T} is intended for building libraries of SIMD operations. Practical use of it requires using llvmcall. The type is defined as:

struct VecElement{T}
    value::T
end

It has a special compilation rule: a homogeneous tuple of VecElement{T} maps to an LLVM vector type when T is a primitive bits type and the tuple length is in the set {2-6,8-10,16}.

At -O3, the compiler might automatically vectorize operations on such tuples. For example, the following program, when compiled with julia -O3 generates two SIMD addition instructions (addps) on x86 systems:

const m128 = NTuple{4,VecElement{Float32}}

function add(a::m128, b::m128)
    (VecElement(a[1].value+b[1].value),
     VecElement(a[2].value+b[2].value),
     VecElement(a[3].value+b[3].value),
     VecElement(a[4].value+b[4].value))
end

triple(c::m128) = add(add(c,c),c)

code_native(triple,(m128,))

However, since the automatic vectorization cannot be relied upon, future use will mostly be via libraries that use llvmcall.

© 2009–2016 Jeff Bezanson, Stefan Karpinski, Viral B. Shah, and other contributors
Licensed under the MIT License.
https://docs.julialang.org/en/release-0.6/stdlib/simd-types/