Performance when chaining multiple macros

General Usage Performance
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1

I’m aware that macros such as @muladd from MuladdMacro.jl, @views, and @inbounds are occasionally very useful for performance. Might there be any problems with combining them in general? For example, is the following chaining of macros valid?

using MuladdMacro
A = rand(100, 100)
B = rand(100, 100)
C = rand(100, 1)
@muladd @views @inbounds @. for j = 1:100
    A[:, j] = C * C + B[:, j] * A[:, j] # Write C^2 = C * C so that @muladd works 
end

Or are there limitations on how far we can chain these individual macros for performance without seeing negative effects?

2

Macros transform code, and there’s no way to guarantee that a series of transformations will be useful (or even valid). You can check with @macroexpand, though:

julia> @macroexpand @muladd @views @inbounds @. for j = 1:100
           A[:, j] = C * C + B[:, j] * A[:, j] # Write C^2 = C * C so that @muladd works
       end
quote
    $(Expr(:inbounds, true))
    local var"#2016#val" = for j = 1:100
                #= REPL[106]:2 =#
                A[:, j] .= (muladd).((Base.maybeview)(B, :, j), (Base.maybeview)(A, :, j), (*).(C, C))
            end
    $(Expr(:inbounds, :pop))
    var"#2016#val"
end
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3

On the other hand, they only impose a performance loss at compilation time. So, if they are used in the body of a function called often with the same parameter types, especially to speed-up loops, then the performance loss should be minimal in comparison to their gains.

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