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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-IE link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>Thanks Eli,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>I didn’t know about this document, and it looks like it has good guidance for other types of debugging too.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'> MartinO<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:#943634'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='color:windowtext;mso-fareast-language:EN-IE'>From:</span></b><span lang=EN-US style='color:windowtext;mso-fareast-language:EN-IE'> Friedman, Eli [mailto:efriedma@codeaurora.org] <br><b>Sent:</b> 30 January 2018 18:36<br><b>To:</b> Martin J. O'Riordan <MartinO@theheart.ie>; 'clang developer list' <cfe-dev@lists.llvm.org><br><b>Subject:</b> Re: [cfe-dev] Possible problem with loop-unrolling, templates and optimisation<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On 1/30/2018 6:26 AM, Martin J. O'Riordan via cfe-dev wrote:<span style='font-size:12.0pt;mso-fareast-language:EN-IE'><o:p></o:p></span></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'>Hi CFE-Devs,</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'>I am investigating a number of regressions in my out-of-tree target since I migrated from LLVM v4 to v5. They have been there a while, but waiting for me to have time to analyse. In all cases the enabling of the loop-unroller seems to cause the problem.</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'>There are 14 failures are in ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>tests/std/containers/unord/unord[multimap]</span><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'>’ and 1 other ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>tests/src/utilities/exchange/exchange.pass.cpp</span><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'>’. All appear to be to do with the list constructors and the list iteration. I can’t see any particular issue with my backend, except that it is for non-interlocked VLIW so scheduling tends to be more sensitive to tiny differences in dependencies than for more traditional targets.</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'>Disabling unrolling, or disabling function inlining seems to fix the problem.</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua ,serif",serif'> </span><o:p></o:p></p></blockquote><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman",serif;mso-fareast-language:EN-IE'><br>I would generally assume this indicates an optimization bug. (That isn't always true; the source code could have undefined behavior. But if the test doesn't have any asan or ubsan failures, there isn't any good way to track down undefined behavior anyway.)<br><br>You probably want to start with <a href="https://llvm.org/docs/OptBisect.html">https://llvm.org/docs/OptBisect.html</a>.<br><br>-Eli<br><br><o:p></o:p></span></p><pre>-- <o:p></o:p></pre><pre>Employee of Qualcomm Innovation Center, Inc.<o:p></o:p></pre><pre>Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project<o:p></o:p></pre></div></body></html>