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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">IIRC, Clang CodeGen will do some branch-to-branch elimination, for blocks that are empty/missing at the source level. Then you have language-mandated things
like RVO? But yeah, the front-end generally doesn't want to do optimizations.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> cfe-dev [mailto:cfe-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>David Blaikie via cfe-dev<br>
<b>Sent:</b> Monday, October 29, 2018 11:00 AM<br>
<b>To:</b> Alexander Zaitsev<br>
<b>Cc:</b> Clang Dev<br>
<b>Subject:</b> Re: [cfe-dev] Which optimizations are done by Clang, not LLVM<o:p></o:p></span></p>
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<p class="MsoNormal">Very few, if any, optimizations are done by Clang - where possible Clang augments the LLVM IR with extra information to enable LLVM to perform the optimizations.<br>
<br>
Clang's IR generation does vary depending on optimization level - but usually on in this sort of attribute-application context. (eg: applying the 'inlinehint' attribute above -O0, applying the 'optnone' attribute at -O0, etc).<br>
<br>
Maybe some of the memcpy optimization (turning struct copying into memcpies) is done in the frontend - because it knows it can copy around the padding bytes if that's more convenient.<br>
<br>
Even very C++-y things like devirtualization are still, ideally, implemented in LLVM - trying to provide as general a tool as possible for frontends to express these kinds of constraints to the LLVM optimization pipeline.<br>
<br>
- Dave<o:p></o:p></p>
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<p class="MsoNormal">On Mon, Oct 29, 2018 at 4:21 AM Alexander Zaitsev via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hello.<br>
<br>
I am trying to find in Clang sources which kind of optimizations do<br>
directly Clang, not LLVM. What I want to do - I have some ideas for<br>
optimization which can be done only for C++ code. And as I understand<br>
Clang is the right place for doing this but I cannot find any example.<br>
<br>
Can you help me a little bit and provide any existent example in Clang<br>
sources?<br>
<br>
Thank you.<br>
<br>
-- <br>
Best regards,<br>
Alexander Zaitsev<br>
<br>
_______________________________________________<br>
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<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a><o:p></o:p></p>
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