<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 Feb 13, 2017, at 2:17 PM, Chandler Carruth <<a href="mailto:chandlerc@gmail.com" class="">chandlerc@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="gmail_quote"><div dir="ltr" class="">On Mon, Feb 13, 2017 at 2:06 PM Gerolf Hoflehner via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:<br 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="gmail_msg"><div class="gmail_msg">For unrolling specifically I agree with Hal that the hooks should be target specific. Actually, I go further and think they should be uArch specific.</div></div></blockquote><div class=""><br class=""></div><div class="">They already are, it is just that no one has contributed a patch to use this on x86 microarchitectures.</div><div class=""><br class=""></div><div class="">Until someone shows up with data showing that we need different tunings for different microarchitectures, it doesn't make sense for us to just make up numbers there.</div><div class=""><br class=""></div><div class="">On the (very limited) microarchitectures we have and can test on, we're not seeing a need for microarchitectural tuning. But if others have different data, that would of course be welcome. That's part of what we're looking for in this thread.</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="gmail_msg"><div class="gmail_msg"> I have no data or prove but would not be surprised to see a wider variety of numbers when the thresholds are tested on a wide range of x86 machines.</div></div></blockquote><div class=""><br class=""></div><div class="">Until we have data, I don't see how we can act on this though.</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="gmail_msg"><div class="gmail_msg">My first thought also was along the lines of Matthias: do it at a higher opt level e.g. O3 or possibly revisit/start thinking about O4.<br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">Why? What about the data presented means that this isn't appropriate at O2? I'm fine if that's the answer, but I think we need to have a clear and unambiguous rationale behind it. With the current data on this thread, the code size and compile time impact seem *very small* except for very small benchmarks, many of which actually show the performance improvement as well.</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="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div dir="ltr" class="gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000" class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911h5"><div class="gmail_msg"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944h5"><blockquote type="cite" class="gmail_msg"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412HOEnZb"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412h5"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412m_-4814779693185880395HOEnZb"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412m_-4814779693185880395h5"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412m_-4814779693185880395m_8897563994913029058h5"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div class="gmail_extra gmail_msg"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412m_-4814779693185880395m_8897563994913029058m_6216879383400100851HOEnZb"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412m_-4814779693185880395m_8897563994913029058m_6216879383400100851h5"><div class="gmail_quote gmail_msg"><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg m_1383633413772573309m_-906165227187887420m_-3091384832346738911m_-223130339941372021m_-7300748067540311944m_5543670116359683412gmail_extra
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</div></blockquote>If there is clear insight where the gains are coming from O2 is fine. IMHO if we just have the “better” numbers we should go for a higher opt level since not everyone will benefit. Some users will only pay higher compile-times.</div><br class=""></body></html>