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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">>
</span>This problem can be solved by sinking the broadcast instruction at codegen-prepare time. <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 considered this option. We currently don’t have target specific optimizations in codegen-prepare time. (Or I’m wrong?)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">And it will be very X86-directed optimization. Even gather-scatter intrinsics are considered as common for all targets.<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">And the second reason, why I’d prefer to generate a splat-GEP, is compile-time saving.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> I should generate 2 (or more, for each splat element) redundant instructions (broadcast is insert+shuffle), hoist them outside the loop on some stage. Then
look for them on CodeGenPreare pass, sink them back and rebuild the CFG.<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>
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<p class="MsoNormal" style="margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo2">
<![if !supportLists]><span style="font-family:"Calibri","sans-serif";color:#31849B"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span dir="LTR"></span><b><i><span style="color:#31849B"> Elena<o:p></o:p></span></i></b></p>
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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>
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<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<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""> Nadav Rotem [mailto:nrotem@apple.com]
<br>
<b>Sent:</b> Monday, March 02, 2015 19:01<br>
<b>To:</b> Demikhovsky, Elena<br>
<b>Cc:</b> llvmdev@cs.uiuc.edu; Duncan P. N. Exon Smith; dag@cray.com; Philip Reames (listmail@philipreames.com); Hal Finkel (hfinkel@anl.gov); Chandler Carruth (chandlerc@gmail.com)<br>
<b>Subject:</b> Re: Extending Vector GEP - proposal<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I don’t have a strong opinion on this. The current GEP syntax is more restrictive and the single base pointer case can be emulated using a broadcast + vector-gep, that can easily be patten matched at codegen time. The problem with the current
syntax is that the ‘broadcast’ instruction can be hoisted outside of loops and this can be a problem with our "one block at a time" codegen implementation. This problem can be solved by sinking the broadcast instruction at codegen-prepare time. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Is there a strong motivation to prefer one representation over the other?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Mar 1, 2015, at 2:10 AM, Demikhovsky, Elena <<a href="mailto:elena.demikhovsky@intel.com">elena.demikhovsky@intel.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Hi,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">According to the current GEP syntax, vector GEP requires that each index must be a vector with the same number of elements.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">%A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">I propose to lessen this requirement. Let each index be or vector or scalar. All vector indices must have the same number of elements. The scalar value will mean the splat
vector value.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">%A = getelementptr i8* %ptr, <4 x i64> %offsets<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">or<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">%A = getelementptr <4 x i8*> %ptrs, i64 %offset<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">In this case we don’t have to add a “broadcast” before GEP. It is actually will be developer’s decision what form to choose.<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">I plan to use vector GEP in gather/scatter and the “broadcasting” of the scalar value impedes to narrow this operation to the “common base, multiple indices” form in the
future.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">What do you think?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Thanks.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:0cm;text-indent:-18.0pt;mso-list:l1 level1 lfo1">
<![if !supportLists]><span style="font-size:10.0pt;font-family:Symbol;color:#31849B"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span dir="LTR"></span><b><i><span style="color:#31849B">Elena</span></i></b><span style="color:#31849B"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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