<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
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--></style></head><body lang=EN-US link=blue vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Sorry,</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I mistook product for sum. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Sent from my Windows 10 phone</p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman",serif'><o:p> </o:p></span></p><div style='mso-element:para-border-div;border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='border:none;padding:0in'><b>From: </b><a href="mailto:sanjoy@playingwithpointers.com">Sanjoy Das</a><br><b>Sent: </b>Wednesday, August 3, 2016 12:24 PM<br><b>To: </b><a href="mailto:code.kchoi@gmail.com">Kevin Choi</a><br><b>Cc: </b><a href="mailto:li1.huang@intel.com">Huang, Li1</a>; <a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br><b>Subject: </b>Re: [llvm-dev] [SCEV] getMulExpr could be extremely slow whencreating SCEVs for a long chain of add/mul instructions</p></div><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman",serif'><o:p> </o:p></span></p><p class=MsoNormal>Hi Kevin,</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Kevin Choi via llvm-dev wrote:</p><p class=MsoNormal> > Correct me if I'm wrong, is the code trying to expand geometric series</p><p class=MsoNormal> > into polynomial expression? (that doesn't sound like a very good thing</p><p class=MsoNormal> > to do, it would spend so much time computing coefficients)</p><p class=MsoNormal> ></p><p class=MsoNormal> > Wouldn't this be better to transform as below:</p><p class=MsoNormal> > mult *= n++ // 30 times</p><p class=MsoNormal> ></p><p class=MsoNormal> > ; into</p><p class=MsoNormal> > mult = mult (n)...(n+29)</p><p class=MsoNormal> > = mult 1...(n+29)/((1)...(n-1))</p><p class=MsoNormal> > = mult * geo_sum(n+29) / geo_sum(n-1) ; is this more expensive</p><p class=MsoNormal> > than leaving as geo series?</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Not sure what you mean by geo_sum -- is geo_sum(n) == 1 * 2 * ... * n?</p><p class=MsoNormal>If so, SCEV does not have a node for that.</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>-- Sanjoy</p><p class=MsoNormal><o:p> </o:p></p></div></body></html>