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</o:shapelayout></xml><![endif]--></head><body lang=EN-IE link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>Sorry, my reply “to all” left out LLVM-Dev<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Martin J. O'Riordan [mailto:MartinO@theheart.ie] <br><b>Sent:</b> 04 April 2018 16:41<br><b>To:</b> 'David Blaikie' <dblaikie@gmail.com>; 'mcrosier@codeaurora.org' <mcrosier@codeaurora.org>; 'Chandler Carruth' <chandlerc@gmail.com>; 'Eric Christopher' <echristo@gmail.com><br><b>Subject:</b> RE: [llvm-dev] [RFC] Adding function attributes to represent codegen optimization level<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>Would implementing GCC’s ‘</span><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>__attribute__((optimize(...)))</span><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>’ help?<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>I can’t find any good documentation for this attribute, but it seems that GCC supports this in two forms:<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>__attribute__((optimize(2)))<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>meaning optimise equivalent to ‘</span><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>-O2</span><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>’, and:<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>__attribute_((optimize("fblah", "O1")))<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>meaning optimise with the provided discrete options.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'> MartinO<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> llvm-dev [<a href="mailto:llvm-dev-bounces@lists.llvm.org">mailto:llvm-dev-bounces@lists.llvm.org</a>] <b>On Behalf Of </b>David Blaikie via llvm-dev<br><b>Sent:</b> 04 April 2018 15:41<br><b>To:</b> <a href="mailto:mcrosier@codeaurora.org">mcrosier@codeaurora.org</a>; Chandler Carruth <<a href="mailto:chandlerc@gmail.com">chandlerc@gmail.com</a>>; Eric Christopher <<a href="mailto:echristo@gmail.com">echristo@gmail.com</a>><br><b>Cc:</b> <a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br><b>Subject:</b> Re: [llvm-dev] [RFC] Adding function attributes to represent codegen optimization level<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p><div><div><p class=MsoNormal>On Tue, Apr 3, 2018 at 12:47 PM via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt'><p class=MsoNormal>All,<br>A recent commit, D43040/r324557, changed the behavior of the gold plugin<br>when compiling with LTO. The change now causes the codegen optimization<br>level to default to CodeGenOpt::Default (i.e., -O2) rather than use the<br>LTO optimization level. The argument was made that the LTO optimization<br>level should control the amount of cross-module optimizations done by<br>LTO, but it should not control the codegen optimization level; that<br>should be based off of the optimization level used during the initial<br>compilation phase (i.e., bitcode generation).<o:p></o:p></p></blockquote><div><p class=MsoNormal><br>At least as I recall the discussion around optnone/optsize in the pass was that these were in some way special semantically distinct properties (optnone being "good for debugging" (or good for debugging compilers - what's the baseline behavior before optimizations are applied), optsize being "make this fit into something it wouldn't otherwise fit into") but that the gradiations of -ON didn't fit into this kind of model & wouldn't ever be implemented as function attributes.<br><br>CC'd Chandler & Eric who I think had opinions/were involved in those previous discussions.<br> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt'><p class=MsoNormal><br>Assuming the argument is reasonable (it make sense to me), I was hoping<br>to solicit feedback on how to proceed. The suggestion in D43040/r324557<br>was to add function attributes to represent the compile-time<br>optimization level (which also seems reasonable to me).<br><br>As a first step, I've put together two patches: 1) an llvm patch that<br>adds the function attributes to the LLVM IR and 2) a clang patch that<br>attaches these attributes to each function based on the codegen<br>optimization level. I then use the function level attributes to<br>"reconstruct" to codegen optimization level used with LTO.<br><br>Please understand this is very much a WIP and just a very small step<br>towards a final solution.<br><br>Here are the patches for reference:<br>Clang: D45226<br>LLVM: D45225<br><br>Regards,<br> Chad<br><br><br>_______________________________________________<br>LLVM Developers mailing list<br><a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></p></blockquote></div></div></div></body></html>