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<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">I think you and I are talking two different things.<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">As far as Intel’s vector function ABI is concerned, unless the programmer specifically says otherwise, given an OpenMP declare simd function, compiler will<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">deduce the VF from HW vector register size and other function signatures. Of course, there can be different vector function ABIs for different targets. Intel<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">compiler cost model uses vector function VF as part of loop vectorization VF determination. So, it’s tightly coupled.<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">A hypothetical vector target may vectorize such a vector function for 4096b vector, with an explicit VF parameter 20 also passed to it, to execute only the lower<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">20-elements parts of the whole thing.<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">I think this scenario answers Philip’s question on why separate mask and VF parameters and why VF can’t be conservatively deduced from the mask/mask compute.<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"><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"><a name="_____replyseparator"></a><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"> Bruce Hoult [mailto:bruce@hoult.org]
<br>
<b>Sent:</b> Thursday, January 31, 2019 5:13 PM<br>
<b>To:</b> Saito, Hideki <hideki.saito@intel.com><br>
<b>Cc:</b> Philip Reames <listmail@philipreames.com>; Robin Kruppe <robin.kruppe@gmail.com>; David Greene <dag@cray.com>; via llvm-dev <llvm-dev@lists.llvm.org>; Maslov, Sergey V <sergey.v.maslov@intel.com>; Topper, Craig <craig.topper@intel.com><br>
<b>Subject:</b> Re: [llvm-dev] [RFC] Vector Predication<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">On Thu, Jan 31, 2019 at 4:31 PM Saito, Hideki via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:</span><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-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">>when we have a mask loaded from an external source (memory, function call boundary, etc...) and a short sequence of vector ops<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Mask value from function call parameter is common. OpenMP declare simd function does exactly that for
the masked cases.</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">Such a mask is at the application level, not at the vector strip-mining loop level.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">As well as possibly being many times longer than the masks the hardware works with, it's likely to not even in the the format the hardware uses: different library APIs might pack a mask into bits, or one mask element per byte, short, or
int.<o:p></o:p></p>
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