<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jul 22, 2017, at 6:23 PM, Hal Finkel 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=""><br 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; -webkit-text-stroke-width: 0px;" class=""><span 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; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">On 07/20/2017 07:58 AM, Dinar Temirbulatov via llvm-dev wrote:</span><br 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; -webkit-text-stroke-width: 0px;" class=""><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;" class=""><blockquote type="cite" class="">it's already implicit that it is dereferenceable for the size of the access (otherwise it would be undefined behavior).<br class=""></blockquote>The values we are loading after restoring those loads are not matter<br class="">for us and it is just that chain of loads for vectorization that<br class="">important for us. And those load would never get rematerialization if<br class="">vectorization is not profitable for the shuffle operation. Once we<br class="">remove the load in instcombine and there is no way to know that memory<br class="">is dereferenceable from the previous load in the chain of loads.<br class=""></blockquote><br 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; -webkit-text-stroke-width: 0px;" class=""><span 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; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">I think you're looking for some kind of "dereferenceable assumption" or "phantom load" that we could put in the IR when we remove an actual load/store to preserve dereferencability information. I think this would need to be an intrinsic, not metadata, because you're interested in putting it at some point in the control flow (e.g. above a loop). There are other use cases for this kind of thing as well, but there are costs to keeping this kind of information, and we'd need to consider this carefully.</span><br 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; -webkit-text-stroke-width: 0px;" class=""></div></blockquote><div><br class=""></div><div>Here is another use case I encountered in the past. InstCombine sinks a load from a block that executed unconditionally in a loop to a conditional block because the load is only used there. Then we fail to vectorize because we think that that would make the load unconditional (which it originally was).</div><div><br class=""></div><div>Adam</div><br class=""><blockquote type="cite" class=""><div class=""><br 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; -webkit-text-stroke-width: 0px;" class=""><span 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; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">-Hal</span><br 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; -webkit-text-stroke-width: 0px;" class=""><br 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; -webkit-text-stroke-width: 0px;" class=""><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;" class=""> Thanks, Dinar.<br class=""><br class="">On Thu, Jul 20, 2017 at 4:07 AM, Filipe Cabecinhas <<a href="mailto:me@filcab.net" class="">me@filcab.net</a>> wrote:<br class=""><blockquote type="cite" class="">Indeed. But the problem here is that Dinar is trying to keep information<br class="">after a load/store is removed by instcombine<br class=""><br class="">For example:<br class=""><br class="">v4sf v = {p[0], p[1], p[2], p[3]};<br class="">v4sf v2 = shuffle(v, 0, 0, 2, 2);<br class=""><br class="">Some pass comes in and removes the p[3] and p[1].<br class=""><br class="">Now you have smaller code, but lost the ability to use a vector load for all<br class="">those values + shuffle. The code got scalarized because we lost the<br class="">information that p[3] is valid.<br class=""><br class="">The attribute on a value/load/something might not be ideal (especially since<br class="">we'd be changing other loads (ones we didn't remove)). But I think Dinar<br class="">wanted to start a conversation about how we can keep this information around<br class="">even after we delete some loads.<br class=""><br class="">Thank you,<br class=""><br class=""> Filipe<br class=""><br class="">On Wed, 19 Jul 2017 at 12:53, Nuno Lopes via llvm-dev<br class=""><<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:<br class=""><blockquote type="cite" class="">When a pointer is passed to load/store, it's already implicit that it is<br class="">dereferenceable for the size of the access (otherwise it would be<br class="">undefined<br class="">behavior).<br class="">Isn't that information sufficient for your use case? (sorry, didn't read<br class="">the whole thread carefully).<br class=""><br class="">Nuno<br class=""><br class="">-----Original Message-----<br class="">From: Dinar Temirbulatov via llvm-dev<br class="">Sent: Tuesday, July 18, 2017 7:36 PM<br class="">Subject: [llvm-dev] [RFC] dereferenceable metadata<br class=""><br class="">Hi,<br class="">While working on PR21780, I used "dereferenceable_or_null" metadata<br class="">and I realized now that it is not correct for my solution to use this<br class="">metadata type since it might point to an address that it is not<br class="">dereferenceable but null. I think that we need another new metadata<br class="">type, something like "dereferenceable" with that we could annotate<br class="">any load (not just pointer type like with dereferenceable_or_null).<br class="">For example, we could annotate this load : "%ld0 = load double,<br class="">double* %ptr, align 8" with dereferenceable<2> and that means that for<br class="">%ptr address memory with length 16-bytes is known to be<br class="">accessible(dereferenceable). Originally in PR21780, InstCombine pass<br class="">removed some loads as dead(in a Scalar IR form) and later that<br class="">prevented us to vectorize the operation, but before removing such<br class="">loads we could annotate the remaining loads in the series with<br class="">"dereferenceable" and later restore IR in a way that is suitable for<br class="">vectorization(see <a href="https://reviews.llvm.org/D35139" class="">https://reviews.llvm.org/D35139</a> ). Also, please note<br class="">that’s the information that is lost when InstCombine kills the last<br class="">load in the series and there is no way to restore this information<br class="">later in following passes.<br class=""> Thanks, Dinar.<br class="">_______________________________________________<br class="">LLVM Developers mailing list<br class=""><a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a><br class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<br class=""><br class="">_______________________________________________<br class="">LLVM Developers mailing list<br class="">llvm-dev@lists.llvm.org<br class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<br class=""></blockquote></blockquote>_______________________________________________<br class="">LLVM Developers mailing list<br class=""><a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a><br class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<br class=""></blockquote><br 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; -webkit-text-stroke-width: 0px;" class=""><span 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; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">--<span class="Apple-converted-space"> </span></span><br 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; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; 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