<div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, May 8, 2021 at 8:15 AM 张驰斌 via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><span lang="EN-US">LLVM Developers,</span></p>
<p class="MsoNormal"><span lang="EN-US"> Hi!</span></p>
<p class="MsoNormal"><span lang="EN-US"> There is a scenario where I want to do full program analysis, ideally after link time optimization is done and before assembly is emitted, when all symbols are in LLVM IR form and contained in a single module.
But after some time browsing stackoverflow, lld documentation, and the mailing lists, I still have little clue how to do it</span>…<span lang="EN-US"> I am aware of the email sent by Y Liu and titled
</span>“<span lang="EN-US">how to add my own passes to LTO pass</span>”<span lang="EN-US">. But it doesn</span>’<span lang="EN-US">t seem to work for the new pass manager. A few questions:</span></p>
<p class="gmail-m_6733311334807343348MsoListParagraph" style="margin-left:39pt">
<u></u><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US" style="font-size:12pt;font-family:SimSun"><span>1.<span style="font:7pt "Times New Roman"">
</span></span></span></span><u></u><span lang="EN-US">The legacy pass manager has an extension point, `PassManagerBuilder::EP_FullLinkTimeOptimizationLast`. Unfortunately, I can</span>’<span lang="EN-US">t find a alternative in the new pass manager. The
`Bye` example seems to suggest using `PB.<span class="gmail-m_6733311334807343348pl-c1">registerVectorizerStartEPCallback`. I am not sure whether doing so will result in my module pass being ran at compile or link time?</span></span></p></div></div></blockquote><div>Feel free to create a patch to add a PassBuilder equivalent of EP_FullLinkTimeOptimizationLast. </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div lang="ZH-CN" style="overflow-wrap: break-word;"><div class="gmail-m_6733311334807343348WordSection1"><p class="gmail-m_6733311334807343348MsoListParagraph" style="margin-left:39pt"><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US" style="font-size:12pt;font-family:SimSun"><u></u><u></u></span></span></p>
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<u></u><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US" style="font-size:12pt;font-family:SimSun"><span>2.<span style="font:7pt "Times New Roman"">
</span></span></span></span><u></u><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US">I wonder how does clang communicates passes that need to be run at lto to lld. The command line that I attempt to get lto running is `clang -fexperimental-new-pass-manager -fpass-plugin=libmymodulepass.so
-flto -fuse-ld=lld </span>…<span lang="EN-US">`. I straced the command for execv calls, and expected to see libmymodulepass.so to be passed to ld.lld as an argument, but found out it wasn</span>’<span lang="EN-US">t. Could you shed some light on how clang
and lld cope with each other during lto?</span></span></p></div></div></blockquote><div>I don't know pass plugins that well, but maybe llvm/examples/Bye/Bye.cpp and its surrounding infrastructure may help?</div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div lang="ZH-CN" style="overflow-wrap: break-word;"><div class="gmail-m_6733311334807343348WordSection1"><p class="gmail-m_6733311334807343348MsoListParagraph" style="margin-left:39pt"><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US" style="font-size:12pt;font-family:SimSun"><u></u><u></u></span></span></p>
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<u></u><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US" style="font-size:12pt;font-family:SimSun"><span>3.<span style="font:7pt "Times New Roman"">
</span></span></span></span><u></u><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US">Greping `ld.lld --help` reveals an interesting option: `--lto-newpm-passes=<value>`. Does the <value> here mean built-in pass names like `dce`/`mem2reg`, or is it an option to insert
our plugin like libmymodulepass.so?</span></span><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US" style="font-size:12pt;font-family:SimSun"><u></u><u></u></span></span></p>
<p class="MsoNormal" style="margin-left:21pt"><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US">I’ve looking into this for a while but haven’t made much progress…Any examples / command line on how to do this are greatly appreciated!<u></u><u></u></span></span></p>
<p class="MsoNormal"><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US"><u></u> <u></u></span></span></p>
<p class="MsoNormal"><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US">Best Wishes,<u></u><u></u></span></span></p>
<p class="MsoNormal"><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US">Chibin Zhang<u></u><u></u></span></span></p>
<p class="MsoNormal"><span class="gmail-m_6733311334807343348pl-c1"><span lang="EN-US">2021.5.8</span></span><span lang="EN-US" style="font-size:12pt;font-family:SimSun"><u></u><u></u></span></p>
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