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<p class="MsoNormal"><span style="color:#1F497D">I did not realized that “truncate” will disappear.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%a = load <8 x i16><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%b = load <8 x i16><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%c = add < 8 x i16><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">store <8 x i16>, %c </span><span style="font-family:Wingdings;color:#1F497D">ç</span><span style="color:#1F497D"> do you need truncating before store?, your original is “store i8”<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal" style="margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo2">
<![if !supportLists]><span style="font-size:12.0pt;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="font-size:12.0pt;font-family:"Times New Roman","serif";color:#31849B"> Elena<o:p></o:p></span></i></b></p>
</div>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<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""> Sam Parker [mailto:sam.parker@arm.com]
<br>
<b>Sent:</b> Monday, May 11, 2015 15:37<br>
<b>To:</b> Demikhovsky, Elena<br>
<b>Cc:</b> llvm-commits@cs.uiuc.edu<br>
<b>Subject:</b> RE: [PATCH] improve vectorizers by removing cost of unnecessary truncs and exts.<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Hi Elena,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">My hope with this patch is that vectorizer recognizes that the backend will not need to generate the truncate instruction.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">For my case, where only i32 types are supported for scalar operations, the IR could look like this:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%a = load i16,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">… (load 7 more data points)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%b = load i16,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">… (load 7 more data points)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%c = sext i8 %a, i32<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">… (repeat for rest of the elements)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%d = sext i8 %b, i32<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">… (repeat for rest of the elements)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%e = add %c, %d<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">… (again, repeat)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%f = trunc i32 %e to i8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">… <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">store i8 %f,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">The vectorizer doesn’t touch it because it’s too expensive to perform the truncations and extensions, but that’s because it doesn’t know that the smaller types are supported by the vector registers. With the
patch, the vectorizer is able to produce this IR:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%a = load <8 x i16><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%b = load <8 x i16><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">%c = add < 8 x i16><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">store <8 x i16>, %c<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Could you elaborate further if this still would not be the case for AVX-512? Or if this is just not legal!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Cheers,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Sam<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<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""> Demikhovsky, Elena [<a href="mailto:elena.demikhovsky@intel.com">mailto:elena.demikhovsky@intel.com</a>]
<br>
<b>Sent:</b> 11 May 2015 12:13<br>
<b>To:</b> Sam Parker<br>
<b>Cc:</b> <a href="mailto:llvm-commits@cs.uiuc.edu">llvm-commits@cs.uiuc.edu</a><br>
<b>Subject:</b> RE: [PATCH] improve vectorizers by removing cost of unnecessary truncs and exts.<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">+ if (Opcode == Instruction::Trunc) {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">+ if (TTI->isTypeLegal(DstVecTy)) {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">+ VecCost = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">+ }<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">On AVX-512 the “truncate” is usually one instruction, the VecCost should be 1.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">On AVX the type may be legal, but “truncate” is more than one instruction.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal" style="margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo2">
<![if !supportLists]><span style="font-size:12.0pt;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="font-size:12.0pt;font-family:"Times New Roman","serif";color:#31849B"> Elena<o:p></o:p></span></i></b></p>
</div>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<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"">
<a href="mailto:llvm-commits-bounces@cs.uiuc.edu">llvm-commits-bounces@cs.uiuc.edu</a> [<a href="mailto:llvm-commits-bounces@cs.uiuc.edu">mailto:llvm-commits-bounces@cs.uiuc.edu</a>]
<b>On Behalf Of </b>Sam Parker<br>
<b>Sent:</b> Monday, May 11, 2015 13:57<br>
<b>To:</b> <a href="mailto:llvm-commits@cs.uiuc.edu">llvm-commits@cs.uiuc.edu</a><br>
<b>Subject:</b> [PATCH] improve vectorizers by removing cost of unnecessary truncs and exts.<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve attached a patch to both the loop vectorizer and slp-vectorizer which checks to see whether truncs and extensions would actually be required if the code was vectorized. This is so that the vectorizers understand that the cost of these
instructions is effectively zero if vectorization happens. This is helpful when working on smaller data types, such as i8 and i16, that do not have native support in general purpose registers, but are supported in vector register files.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Regards,<o:p></o:p></p>
<p class="MsoNormal">Sam<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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