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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I’m not sure the transformation happening with fdiv is correct. If we have “%y = fdiv float %x, undef” and %x is a NaN then the result will be NaN for any value
of the undef, right? So if I understand the undef rules correctly (never a certainty) then we can’t safely replace the expression with undef. We could, I think, replace it with “%y = %x” though. I think the same is true for fadd, fsub, fmul, and frem.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-Andy<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></a></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Sanjay Patel [mailto:spatel@rotateright.com]
<br>
<b>Sent:</b> Tuesday, February 27, 2018 6:29 PM<br>
<b>To:</b> llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Cc:</b> Nuno Lopes <nunoplopes@sapo.pt>; Stephen Canon <scanon@apple.com>; David Majnemer <david.majnemer@gmail.com>; John Regehr <regehr@cs.utah.edu>; Kaylor, Andrew <andrew.kaylor@intel.com>; Sanjoy Das <sanjoy@playingwithpointers.com>; Friedman, Eli <efriedma@codeaurora.org>;
Matt Arsenault <arsenm2@gmail.com><br>
<b>Subject:</b> how to simplify FP ops with an undef operand?<o:p></o:p></span></p>
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<p class="MsoNormal">%y = fadd float %x, undef<o:p></o:p></p>
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<p class="MsoNormal">Can we simplify this? <br>
<br>
Currently in IR, we do nothing for fadd/fsub/fmul. For fdiv/frem, we propagate undef. The code comment for fdiv/frem says:<br>
"the undef could be a snan"<o:p></o:p></p>
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<p class="MsoNormal">If that's correct, then shouldn't it be the same for fadd/fsub/fmul? But this can't be correct because we support targets that don't raise exceptions...and even targets that raise exceptions do not trap by default on snan?<o:p></o:p></p>
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