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</o:shapelayout></xml><![endif]--></head><body lang=EN-IE link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>While investigating a new bug in some code using our LLVM v3.9.0 derived compiler, it turns out that it now emits ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>.p2align</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ unconditionally if the alignment value is a power of 2. Previously this was dependent on ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MAI->getAlignmentIsInBytes()</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>We don’t support non-power-of 2 alignment anyway, but our assembler does not support ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>.p2align</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ and there appears to be no way of changing this in a target configurable way.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>There have been emails about the fact that the ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ implementation is hidden, and the argument is that if the target needs something different it can implement its own specialisation of ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCStreamer</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’. While this is technically true, but ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ already does more than 90% of what I need, and to implement my own specialisation really means cloning ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’, and editing those few places where my assembly requirements are different to it. And then the target that does this clone is required to carefully track future revisions of ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ to ensure that their clone is still a clone.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>Generally it is good practice to reuse existing code, and specialise only for the differences, so it really make a lot more sense to publish it in a header, and allow the target to sub-class it with overrides for each of the methods it wants to handle differently.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>As it is, I have had to add yet another tweak to this code, all of which are relatively trivial:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:12.0pt;font-family:Symbol'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer::EmitAssignment</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ changed to implement aliases as ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>.alias symA symB</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ instead of ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>symA - symB</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:12.0pt;font-family:Symbol'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer::EmitBytes</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ to break long ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>.byte</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ sequences into multiple ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>.byte</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ sequences on multiple lines (actually, I could retire this change as our assembler now handles the long sequences)<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:12.0pt;font-family:Symbol'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer::EmitFill</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ because we need an additional argument in the directive<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:12.0pt;font-family:Symbol'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer::EmitValueToAlignment</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ to use ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>.align</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ instead of ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>.p2align</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>These are such small changes that it really does not warrant me cloning 1,600 lines of code so that I can tweak 8 of them, and being able to sub-class the otherwise very useful ‘</span><span style='font-size:12.0pt;font-family:"Courier New"'>MCAsmStreamer</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ class would greatly simplify adapting LLVM for non-</span><span style='font-size:12.0pt;font-family:"Courier New"'>gas</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'> compliant assemblers. It seems to me that splitting this file into a source and a header is not going to create maintenance problems for LLVM, while at the same time it would greatly simplify the implementation of compilers for non-mainstream assemblers.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'> MartinO<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p></div></body></html>