Writing @inbounds in code is tedious, and ruins the nice alignment of for loops. Is it really necessary? It feels like in simple loops like n = length(x) for i = 1:n x[i] *= 2 end this should be something the compiler could figure out by itself. Is this something that is Intrinsically impossib…

I think it is much better to be explicit with bounds-check removal than to have to constantly think “will the compiler be able to figure out removing the bound checks here”. In addition, bounds check are in the majority of cases a non-issue. It will almost only matter in cases where it inhibits oth…

I agree that broadcast is best when it can be used, but it’s not always the case. A lot of package code seems to be littered with @inbounds, and it’s recommended in the performance tips, so that it becomes a habit for people to write @inbounds everywhere, which makes coding less pleasant. If there …

[image] antoine-levitt: it becomes a habit for people to write @inbounds everywhere Well… don’t do that. [image] antoine-levitt: when the compiler can prove that the index will be in bounds This is almost impossible to reason about and you would have to add it anyway, just to make sur…

[image] antoine-levitt: it’s recommended in the performance tips, so that it becomes a habit for people to write @inbounds everywhere It is possible that you misread the relevant part of the manual , which claims that Sometimes you can enable better optimization by promising certain program …

I think the need to be careful is exaggerated: unit tests ignore @inbounds so if you do get a SEGFAULT, that’s more a statement about insufficient unit tests than it is a statement about bad coding.

Yeah, it’s not like any other languages have had problems with non-existing bounds checks. Clearly, they should just have written more unit tests. Come on now…

There’s also the command line argument --check-bounds https://docs.julialang.org/en/stable/manual/getting-started/#Getting-Started-1 --check-bounds={yes|no} Emit bounds checks always or never (ignoring declarations)

I should add that the original example n = length(x) for i = 1:n x[i] *= 2 end is definitely not a safe place to use @inbounds, as you cannot assume arrays are 1-based. See e.g. https://docs.julialang.org/en/latest/devdocs/offset-arrays/#Background-1 This would be, though: for i in linearindic…

My point was that, in the most common setting of Array (as opposed to general AbstractArray) whose functions are not overloaded, the compiler could recognize that any index between 1 and length(x) is inbounds (and similar for multidimensional iteration, and several other “classical” array types). Of…

Still it’s a nice demonstration of the need to be careful with @inbounds

Is @inbounds really necessary?

General Usage

kristoffer.carlsson August 31, 2017, 9:40am 4

Well… don’t do that.

This is almost impossible to reason about and you would have to add it anyway, just to make sure.

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Is @inbounds really necessary?

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