<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 Jan 30, 2017, at 10:49 AM, Dehao Chen 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=""><div dir="ltr" class="">Currently, loop fully unroller shares the same default threshold as loop dynamic unroller and partial unroller. This seems conservative because unlike dynamic/partial unrolling, fully unrolling will not affect LSD/ICache performance. In <a href="https://reviews.llvm.org/D28368" class="">https://reviews.llvm.org/D28368</a>, I proposed to double the threshold for loop fully unroller. This will change the codegen of several SPECCPU benchmarks:<div class=""><br class=""></div><div class=""><p style="margin: 0px 0px 12px; padding: 0px; border: 0px; font-family: 'segoe ui', 'segoe ui web regular', 'segoe ui symbol', lato, 'helvetica neue', helvetica, arial, sans-serif; font-size: 13px;" class="">Code size:<br style="margin-top:0px" class="">447.dealII 0.50%<br class="">453.povray 0.42%<br class="">433.milc 0.20%<br class="">445.gobmk 0.32%<br class="">403.gcc 0.05%<br class="">464.h264ref 3.62%</p><p style="margin: 0px 0px 12px; padding: 0px; border: 0px; font-family: 'segoe ui', 'segoe ui web regular', 'segoe ui symbol', lato, 'helvetica neue', helvetica, arial, sans-serif; font-size: 13px;" class="">Compile Time:<br style="margin-top:0px" class="">447.dealII 0.22%<br class="">453.povray -0.16%<br class="">433.milc 0.09%<br class="">445.gobmk -2.43%<br class="">403.gcc 0.06%<br class="">464.h264ref 3.21%</p><p style="margin: 0px 0px 12px; padding: 0px; border: 0px; font-family: 'segoe ui', 'segoe ui web regular', 'segoe ui symbol', lato, 'helvetica neue', helvetica, arial, sans-serif; font-size: 13px;" class="">Performance (on intel sandybridge):<br style="margin-top:0px" class="">447.dealII +0.07%<br class="">453.povray +1.79%<br class="">433.milc +1.02%<br class="">445.gobmk +0.56%<br class="">403.gcc -0.16%<br class="">464.h264ref -0.41%</p></div></div></div></blockquote><br class=""><div>Can you clarify how to read these numbers? (I’m using +xx% to indicates a slowdown usually, it seems you’re doing the opposite?).</div><div><br class=""></div><div>So considering 464.h264ref, does it mean it is 3.6% slower to compile, gets 3.2% larger, and 0.4% slower?</div><div><br class=""></div><div>Another question is about PGO integration: is it already hooked there? Should we have a more aggressive threshold in a hot function? (Assuming we’re willing to spend some binary size there but not on the cold path).</div><div><br class=""></div><div>Thanks,</div><div><br class=""></div><div>— </div><div>Mehdi</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><p style="margin: 0px 0px 12px; padding: 0px; border: 0px; font-family: 'segoe ui', 'segoe ui web regular', 'segoe ui symbol', lato, 'helvetica neue', helvetica, arial, sans-serif; font-size: 13px;" class="">Looks like the change has overall positive performance impact with very small code size/compile time overhead. Now the question is shall we make this change default in O2, or shall we leave it in O3. We would like to have more input from the community to make the decision.</p><p style="margin: 0px 0px 12px; padding: 0px; border: 0px; font-family: 'segoe ui', 'segoe ui web regular', 'segoe ui symbol', lato, 'helvetica neue', helvetica, arial, sans-serif; font-size: 13px;" class="">Thanks,</p><p style="margin: 0px 0px 12px; padding: 0px; border: 0px; font-family: 'segoe ui', 'segoe ui web regular', 'segoe ui symbol', lato, 'helvetica neue', helvetica, arial, sans-serif; font-size: 13px;" class="">Dehao</p></div></div>
_______________________________________________<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=""></div></blockquote></div><br class=""></body></html>