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<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A">I have no example side effects in hand. But LLVM targets a bunch of architectures, and who knows what the future holds. So it may be prudent to not promise too much so as to leave ourselves
an escape hatch.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A">Doesn’t LLVM target some chips that have floating point instruction sets that are not IEEE compliant? Can we be certain that no new LLVM target will ever have to jump through hoops to
avoid side effects simply because we promised that fneg would never, ever have any side effects?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A">Assuming we do promise no side effects from fneg, ever and forever, then the documentation should say that clearly.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>From:</b> Cameron McInally <cameron.mcinally@nyu.edu> <br>
<b>Sent:</b> Wednesday, September 26, 2018 3:03 PM<br>
<b>To:</b> Kevin Neal <Kevin.Neal@sas.com><br>
<b>Cc:</b> LLVM Developers Mailing List <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [llvm-dev] [FPEnv] FNEG instruction<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p><b><i><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:red">EXTERNAL</span></i></b><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:red">
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<p class="MsoNormal">On Wed, Sep 26, 2018 at 2:47 PM Kevin Neal <<a href="mailto:Kevin.Neal@sas.com">Kevin.Neal@sas.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Courier New";color:#44546A">Well, yes, they are different operations. And, yes, this needs to be corrected. This wasn’t my point. It’s a given.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Courier New";color:#44546A"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Courier New";color:#44546A">I was getting at the _<i>declared</i>_ absence of side effects and what promises we make to anyone using the new fneg instruction.
Is this a promise we want to make?</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">What are the side effects that you're thinking about? <o:p></o:p></p>
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