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<p class="MsoNormal"><span style="font-family:Consolas;color:#1F497D">It provides a useful starting point, but I agree with Jim that it is not a complete solution and requires rework of the results in a lot cases. I think we could improve it further to address
these issues but that work is nontrivial. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:Consolas;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:Consolas;color:#1F497D">If you are deciding between a quick and dirty implementation of a custom backend vs. the C backend, then the C backend is sometimes preferable in my experience although it depends on the
complexity of the code you are trying to run and how often you need to change it.<o:p></o:p></span></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""> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu]
<b>On Behalf Of </b>Jim Grosbach<br>
<b>Sent:</b> Tuesday, August 19, 2014 2:12 PM<br>
<b>To:</b> Bruce Hoult<br>
<b>Cc:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] C Backend Ressurected<o:p></o:p></span></p>
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<p class="MsoNormal">This is part of the problem with the C backend. This is very much not what it’s useful for, yet it very much looks like it is. The LLVM IR is target dependent, including things like structure layout, pointer size, and other ABI issues.
Even with a resurrected C backend, you can’t use it as a substitute for real target support.<o:p></o:p></p>
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<p class="MsoNormal">-Jim<o:p></o:p></p>
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<p class="MsoNormal">On Aug 18, 2014, at 7:02 PM, Bruce Hoult <<a href="mailto:bruce@hoult.org">bruce@hoult.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">I don't know how good it is, but the applications seem obvious. e.g. compiling programs in any of a number of original formats to run natively on CPUs that have a working simple C compiler (maybe only K&R or C89) but don't have an LLVM
back end.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The source program could be in modern C, C++, or any other high level language or assembly language with a translator to LLVM.<o:p></o:p></p>
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<p class="MsoNormal">On Tue, Aug 19, 2014 at 1:40 PM, Jun Koi <<a href="mailto:junkoi2004@gmail.com" target="_blank">junkoi2004@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">On Mon, Aug 18, 2014 at 9:18 PM, Carback, Richard T., III <<a href="mailto:rcarback@draper.com" target="_blank">rcarback@draper.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas">Hi All,</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas">2 of my summer interns (Aimee Dipietro and Greg Simpson) used their time over the summer to resurrect the LLVM C Backend:
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas"><a href="https://github.com/draperlaboratory/llvm-cbe" target="_blank">https://github.com/draperlaboratory/llvm-cbe</a></span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas">Improvements include recovery of simple for/while loops (instead of goto), better variable naming, inline asm support, and making it work on a
more recent version of llvm. I believe they used the repository here as a starting point:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas"><a href="https://github.com/glycerine/llvm/tree/cbe_revival" target="_blank">https://github.com/glycerine/llvm/tree/cbe_revival</a></span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:Consolas">Feedback is welcomed. I would like to see this feature put back into LLVM, and any help on how to make that happen would be appreciated.</span><o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">would you mind explaining what this backend is for, and its applications?<o:p></o:p></p>
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<p class="MsoNormal">i guess it is to get the C code at the output of the backend, but dont get why we need it.<br>
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thanks,<o:p></o:p></p>
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<p class="MsoNormal">Jun<o:p></o:p></p>
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