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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;color:black'>At the moment I am in the process of getting our out-of-tree compiler up to date with respect to the v4.0 branch, and thankfully all is going well. However, one of the most common changes I have had to make has to do with iterations over machine instructions and basic blocks.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>These are changes I have had to make incrementally each time we catch up with a release of LLVM, and basically the issue is that I have to replace something like:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New";color:black'>void foo(MachineInstruction* x);<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New";color:black'>MachineBasicBlock::iterator index = ...;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New";color:black'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New";color:black'>foo(index);<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>to:<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New";color:black'>foo(<span style='background:yellow;mso-highlight:yellow'>&*</span>index);<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>This pattern of having to make this edit (adding the ‘</span><span style='font-size:12.0pt;font-family:"Courier New";color:black;background:yellow;mso-highlight:yellow'>&*</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>’) looks really scary to me, I am always nervous of expressions that look like this, and over the past three or so releases we have had to make similar changes (usually, but not always to various MI/MBB iterators).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>So my guess is that we are using the wrong iterator, or an inappropriate iterator; but there are so many iterators now that I wonder if there is guidance on which iterator is most appropriate to a particular context or usage.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>The main types of iteration we need are over the instructions in a basic-block, sometimes including the MI contents of bundles, and sometimes over the bundle (treating them as a single MI). And of course the ‘</span><span style='font-size:12.0pt;font-family:"Courier New";color:black'>const</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>’ versus editable iterations.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>Does anybody have pointers to existing developer documentation advising which iterators to use, when and how? Or have advice they can give here in this forum if such documentation does not exist (I haven’t found it if it does exist)?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>I think it would be really useful information in general, and since our code is originally derived from LLVM v2.7, as LLVM modernises, we often have to make tweaks to code built a long time ago to get it working again. The trick of adding ‘</span><span style='font-size:12.0pt;font-family:"Courier New";color:black;background:yellow;mso-highlight:yellow'>&*</span><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>’ works, but is deeply inelegant and error-prone, and I’m pretty sure that it can be made a lot cleaner if we use the right iterator for the job.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'>Thanks for your advice,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'> MartinO<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Book Antiqua",serif;color:black'><o:p> </o:p></span></p></div></body></html>