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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Hi Jerry,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">The way I understand it, the auto-vectorizer decides whether to “Widen” an instruction into a vector instruction is by calling one of the “get*Cost”
methods of the <a href="https://llvm.org/doxygen/classllvm_1_1TargetTransformInfo.html">
TargetTransformInfo</a> class. For example, take a look at <a href="https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp#L6356">
this line in LoopVectorize.cpp</a> which is calling the </span><span style="font-size:11.0pt;font-family:Consolas;color:#005CC5;background:white"><a href="https://github.com/llvm/llvm-project/blob/master/llvm/lib/Analysis/TargetTransformInfo.cpp#L690">TTI.getArithmeticInstrCost</a></span><span style="font-size:9.0pt;font-family:Consolas;color:#005CC5;background:white">
</span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">for all the basic arithmetic instruction cases, and it passes in the instruction opcode, Vector Type and any other info needed. These get*Cost calls eventually
end up with one of the <Backend>TargetTransformInfo methods, for example <a href="https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp#L827">
this is the ARM backend implementation</a> for calculating the vector arithmetic instruction costs.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">So I believe all you need to do to tune the auto-vectorizer for your backend is to implement a subclass of
<a href="http://llvm.org/doxygen/classllvm_1_1BasicTTIImplBase.html#details">BaseTTIImplBase<T></a> as done
<a href="https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/ARM/ARMTargetTransformInfo.h#L51">
here for ARM</a> and then implement the appropriate get*Cost methods to return proper costs for your backend along with the getST and getTLI methods which are needed by the BaseTTIIimpl class. A few other methods you might need to implement for your <Backend>TargetTransformInfo
are the getNumberOfRegisters to return the number of registers for a given (VectorType) RegisterClass, getMinimumVF (for the minimum vectorization factor for your subtarget), etc. You can take a look at any of the existing backend TTI implementations to get
an idea as to how these methods have to be implemented.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">P.S. I’m still relatively new to LLVM (little over 7 months of experience working on an LLVM backend), so I apologize if I’ve made any mistakes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Anirudh<o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> llvm-dev <llvm-dev-bounces@lists.llvm.org>
<b>On Behalf Of </b>??? via llvm-dev<br>
<b>Sent:</b> Thursday, July 16, 2020 8:48 AM<br>
<b>To:</b> llvm-dev@lists.llvm.org<br>
<b>Subject:</b> [EXT] [llvm-dev] auto simd<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">Hi, there<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">I am doing optimization for an new backend. And I have read the auto-vectorization guide,<a href="https://llvm.org/docs/Vectorizers.html.">https://llvm.org/docs/Vectorizers.html.</a><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">The hardware support vector operation. I wonder how can I get the loop vectorizer tuned for my backend. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">Is there any documents or suggestions? Thanks!<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">Best regards,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">Jerry<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><o:p> </o:p></p>
<p> <o:p></o:p></p>
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