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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Right, not memcpy/memmove, sorry I should be more careful about that stuff.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">REP MOVS looks like the right thing though. Does LLVM know how to produce that?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<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""> scanon@apple.com [mailto:scanon@apple.com]
<br>
<b>Sent:</b> Thursday, November 10, 2016 2:24 PM<br>
<b>To:</b> Robinson, Paul<br>
<b>Cc:</b> Ryan Taylor; Bagel; llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] array fill idioms<o:p></o:p></span></p>
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<p class="MsoNormal">On Nov 10, 2016, at 5:15 PM, Robinson, Paul via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Back in the day, we called this a BLT (block transfer, pronouced 'blit') for the PDP-10 instruction of that name.</span><o:p></o:p></p>
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<p class="MsoNormal">On x86, there is REP MOVS.<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">You can do this by assigning the first value, then do an overlapping memcpy to fill in the rest.</span><o:p></o:p></p>
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<p class="MsoNormal">This is undefined behavior, and really doesn’t work with most modern memcpy( ) implementations (the most common thing these days is to simply implement memmove( ) semantics for memcpy, which will very much not do what you want).<o:p></o:p></p>
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<p class="MsoNormal">– Steve<o:p></o:p></p>
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