<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">I've never seen the Swift compiler put array storage on automatic storage, even for small arrays. I don't think that it has much to do with their size, though (for any array that is not incredibly large).</div><br class=""><div><blockquote type="cite" class=""><div class="">Le 3 août 2017 à 23:18, David Hart <<a href="mailto:david@hartbit.com" class="">david@hartbit.com</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Don’t small arrays live on the stack?<div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On 4 Aug 2017, at 06:35, Félix Cloutier via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">As far as I can tell, currently, all arrays live on the heap.</div><br class=""><div class=""><blockquote type="cite" class=""><div class="">Le 3 août 2017 à 19:03, Robert Bennett via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class=""></div><div class="">Where do constant Arrays currently live? I hope the answer is on the stack, since their size doesn’t change.</div><div class=""><br class="">On Aug 3, 2017, at 8:44 PM, Taylor Swift via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><br class=""><div class="gmail_extra"><br class=""><div class="gmail_quote">On Thu, Aug 3, 2017 at 8:20 PM, Karl Wagner via swift-evolution <span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><span class=""><div class=""><blockquote type="cite" class=""><div class=""><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap:break-word" class=""><div class=""><br class=""></div><div class="">The root cause, of course, is that the VLAs require new stack allocations each time, and the stack is only deallocated as one lump when the frame ends.</div></div></div></blockquote><div class=""><br class=""></div><div class="">That is true of alloca(), but not of VLAs. VLAs are freed when they go out of scope.</div><div class=""><br class=""></div></div></div></blockquote></div><br class=""></span><div class="">Learned something today.</div><div class=""><br class=""></div><div class="">Anyway, if the goal is stack allocation, I would prefer that we explored other ways to achieve it before jumping to a new array-type. I’m not really a fan of a future where [3; Double] is one type and (Double, Double, Double) is something else, and Array<Double> is yet another thing.</div></div></blockquote><div class=""><br class=""></div><div class="">They are completely different things. <br class=""><br class=""></div><div class="">[3; Double] is three <i class="">contiguous</i> Doubles which may or may not live on the stack. <br class=""><br class=""></div><div class="">(Double, Double, Double) is three Doubles bound to a single variable <i class="">name</i>, which the compiler can rearrange for optimal performance and may or may not live on the stack. <br class=""><br class=""></div><div class="">Array<Double> is an vector of Doubles that can dynamically grow and always lives in the heap.<br class=""></div><div class=""> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><div class=""><br class=""></div><div class="">From what I’ve read so far, the problem with stack-allocating some Array that you can pass to another function and which otherwise does not escape, is that the function may make an escaping reference (e.g. assigning it to an ivar or global, or capturing it in a closure).</div><div class=""><br class=""></div><div class="">How about if the compiler treated every Array it receives in a function as being potentially stack-allocated. The first time you capture it, it will check and copy to the heap if necessary. All subsequent escapes (including passing to other functions) use the Array known to be allocated on the heap, avoiding further checking or copying within the function.</div><div class=""><br class=""></div><div class="">The same goes for Dictionary, and really any arbitrary value-type with COW storage. The memory that those types allocate is part of the value, so it would be cool if we could treat it like that.</div></div>
<br class=""></blockquote></div><br class=""></div><div class="gmail_extra">This is not true. FSAs have nothing to do with automatic storage, their static size only makes them <i class="">eligible</i> to live on the stack, as tuples are now. The defining quality of FSAs is that they are static and contiguous. <br class=""></div></div>
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