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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I'd prefer to retain the cost table code as C++ rather than have it moved to a "build-time" table-gen file. However, I'm not actively submitting patches in
that area at the moment and I'll defer to others' opinions on the issue.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Dave<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Chandler Carruth [mailto:chandlerc@google.com]
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<b>Sent:</b> 24 January 2013 08:45<br>
<b>To:</b> Renato Golin Linaro<br>
<b>Cc:</b> LLVM Commits; Nadav Rotem; David Tweed; Evan Cheng<br>
<b>Subject:</b> Re: Cost Table, take 2<o:p></o:p></span></p>
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<p class="MsoNormal">At this point, I'm not really seeing the benefit of this patch.<o:p></o:p></p>
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<p class="MsoNormal">It takes 2 structs and 2 functions, both of which are dead simple, and replaces them with 3 class templates in an inheritance tree plus an inner struct a constructor and one function that is significantly more complex. It doesn't make things
more efficient in the process. It doesn't really make this a generic tool for table lookup, because the tables are not in fact generic. I think ultimately I would prefer the original code here. Maybe there is a massive simplification this provides to some
future code you're considering that I don't see yet? Dunno...<o:p></o:p></p>
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<p class="MsoNormal">Sorry for being a bit of a rain cloud here. To try to give some constructive ideas, I looked at the fundamental problem, and I see two designs that seem more workable:<o:p></o:p></p>
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<p class="MsoNormal">1) A TargetCostTable class template in include/llvm/Target which accepts a T type parameter that can be either MVT, std::pair<MVT, MVT>, or std::tuple<MVT, MVT, ...>. Then the ISD and the cost value can be concrete things.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">2) Teach tablegen to produce pre-sorted tables with lookup routines from a .td file in the target.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">My suspicion is that #1 will end up being nearly as much code and complexity as the duplication between ARM and X86....<o:p></o:p></p>
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<p class="MsoNormal">My suspicion is that *if* it is worth abstracting this stuff, we should just do #2 and make it really powerful. Then we can quickly build very large and detailed cost tables, and they will remain efficient and simple to use in each target.<o:p></o:p></p>
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