<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 2020 Nov 27, at 20:45, Chris Lattner via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.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; line-break: after-white-space;" class=""><div class="">Sorry for falling off the map on this thread:</div><div class=""><br class=""></div>On Nov 17, 2020, at 1:42 PM, David Blaikie <<a href="mailto:dblaikie@gmail.com" class="">dblaikie@gmail.com</a>> wrote:<div class=""><blockquote type="cite" class=""><div class=""><div class="Singleton"><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none;" class="">Thoughts/suggestions:<br class="">- Adding the default seems very reasonable to me, and I think that 64 bytes is a good default. I think you should change the behavior so that SmallVector<LargeThing> defaults to a single inline element instead of zero though. Perhaps generate a static_assert when it is crazy large.<br class=""></blockquote><br style="caret-color: rgb(0, 0, 0); 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; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); 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; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Out of curiosity: Why a single rather than zero?</span><br style="caret-color: rgb(0, 0, 0); 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; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""></div></div></blockquote></div><br class=""><div class="">My rationale for this is basically that SmallVector is typically used for the case when you want to avoid an out-of-line allocation for a small number of elements, this was the reason it was created. While there is some performance benefits of SmallVector<T,0> over std::vector<> they are almost trivial.</div></div></div></blockquote><div><br class=""></div><div>The performance benefits aren't trivial.</div><div><br class=""></div><div>std::vector grow operations will refuse to use std::move for some T, a pessimization required by its exception guarantees, even if you're building with `-fno-exceptions`. We had a massive compile-time problem in 2016 related to this that I fixed with 3c406c2da52302eb5cced431373f240b9c037841 by switching to SmallVector<T,0>. You can see the history in r338071 / 0f81faed05c3c7c1fbaf6af402411c99d715cf56.</div></div></body></html>