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</o:shapelayout></xml><![endif]--></head><body lang=EN-IE link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>I must admit, I prefer the shuffle canonicalization, but mainly because we have put a lot of effort into finding optimal instruction sequences for obscure shuffle patterns. But we could refactor easily enough to use either.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>I don’t know which makes the most logical sense in this case though. Certainly choosing the select pattern better matches OpenCL’s native select interface.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'> MartinO<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org] <b>On Behalf Of </b>Michael Kuperstein via llvm-dev<br><b>Sent:</b> 29 August 2016 19:28<br><b>To:</b> Philip Reames <listmail@philipreames.com><br><b>Cc:</b> llvm-dev <llvm-dev@lists.llvm.org><br><b>Subject:</b> Re: [llvm-dev] IR canonicalization: vector select or shufflevector?<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>I have a slight preference towards shufflevector, because it makes sequences of shuffles, where only some of the shuffles can be converted into selects (because the input and output vector sizes of the others don't match) simpler to reason about.<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>I'm not sure this is a particularly good reason, though.<o:p></o:p></p></div></div></div><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On Mon, Aug 29, 2016 at 8:19 AM, Philip Reames via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><p>I don't have a strong preference, though it is clear we should pick one. I'd mildly prefer the select form for readability. From an optimization standpoint, I see reasonable arguments for either. <o:p></o:p></p><p>Philip<o:p></o:p></p><div><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On 08/28/2016 12:37 PM, Sanjay Patel via llvm-dev wrote:<o:p></o:p></p></div></div></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><div><div><div><p class=MsoNormal style='margin-bottom:12.0pt'>A vector select with a constant vector condition operand:<br><br>define <4 x i32> @foo(<4 x i32> %a, <4 x i32> %b) {<br> %sel = select <4 x i1> <i1 true, i1 false, i1 false, i1 true>, <4 x i32> %a, <4 x i32> %b<br> ret <4 x i32> %sel<br>}<br><br><br>...is equivalent to a shufflevector:<br><br>define <4 x i32> @goo(<4 x i32> %a, <4 x i32> %b) {<br> %shuf = shufflevector <4 x i32> %a, <4 x i32> %b, <4 x i32> <i32 0, i32 5, i32 6, i32 3><br> ret <4 x i32> %shuf<br>}<br><br><br>For the goal of canonicalization in IR, which of these should we prefer? Some backend / lowering differences for AArch64 and PPC are noted in:<br><a href="https://llvm.org/bugs/show_bug.cgi?id=28530" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=28530</a><br><a href="https://llvm.org/bugs/show_bug.cgi?id=28531" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=28531</a><o:p></o:p></p></div><p class=MsoNormal>x86 converts either form optimally in all cases I've looked at.<o:p></o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><br>This question first came up in D22114 ( <a href="https://reviews.llvm.org/D22114" target="_blank">https://reviews.llvm.org/D22114</a> ) and is extended in D23886 ( <a href="https://reviews.llvm.org/D23886" target="_blank">https://reviews.llvm.org/D23886</a> ) with a constant value example.<o:p></o:p></p></div></div><p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p></div></div><pre>_______________________________________________<o:p></o:p></pre><pre>LLVM Developers mailing list<o:p></o:p></pre><pre><a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><o:p></o:p></pre><pre><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></pre></blockquote><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal style='margin-bottom:12.0pt'><br>_______________________________________________<br>LLVM Developers mailing list<br><a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></p></blockquote></div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>