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<li class="MsoNormal" style="color:windowtext;mso-list:l0 level1 lfo1"><span style="color:black">Looks like some sort of pass ordering issue; it will vectorize if indvars runs sometime between loop unswitch and the vectorizer.</span><o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.25in">That insight is helpful. I scheduled Canonicalization of induction variable before loop vectorization and could get the loop vectorized.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.25in">The indvars are heavily dependent on SCEV. If there a scalar like tmp which is of real type, we may not be able to get the indvars sorted out because of the integer type limitation in SCEV!<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:.25in">
Is there a way out when we have a scalar float computation that is dependent on induction variable?<span style="color:windowtext"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">-Ganesh<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><b><span style="color:windowtext">From:</span></b><span style="color:windowtext"> Friedman, Eli [mailto:efriedma@codeaurora.org]
<br>
<b>Sent:</b> Saturday, May 12, 2018 12:36 AM<br>
<b>To:</b> Gopalasubramanian, Ganesh <Ganesh.Gopalasubramanian@amd.com>; llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Query on unswitching + vectorization<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">On 5/10/2018 10:44 PM, Gopalasubramanian, Ganesh via llvm-dev wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Calibri Light ,sans-serif",serif">Hi,</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Calibri Light ,sans-serif",serif"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Calibri Light ,sans-serif",serif">I am going through analysis on unswitching + vectorization.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Calibri Light ,sans-serif",serif">For the below test, llvm unswitches successfully but fails to vectorize the loop after unswitching.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Calibri Light ,sans-serif",serif">Llvm bails out saying “Found an outside user” apparently which is the value of ‘tmp’.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Arial",sans-serif"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif">int i, w, x[1000], y[1000],tmp;</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif">void fn()</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif">{</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> for (i = 0; i < 1000; i++) {</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> if (w==1) {</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> y[i] = 1; tmp = i*2;</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> }</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> else if (w==2) {</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> y[i] = 2; tmp = i*4;</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> }</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> x[i] += y[i] + tmp;</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> }</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif">}</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New",serif"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Calibri Light ,sans-serif",serif">GCC vectorizes the loop after unswitching/if conversion. Request your help in vectorizing this loop.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Calibri Light ,sans-serif",serif"> </span><o:p></o:p></p>
</blockquote>
<p class="MsoNormal" style="margin-left:.5in"><br>
Looks like some sort of pass ordering issue; it will vectorize if indvars runs sometime between loop unswitch and the vectorizer.<br>
<br>
-Eli<br>
<br>
<br>
<o:p></o:p></p>
<pre style="margin-left:.5in">-- <o:p></o:p></pre>
<pre style="margin-left:.5in">Employee of Qualcomm Innovation Center, Inc.<o:p></o:p></pre>
<pre style="margin-left:.5in">Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project<o:p></o:p></pre>
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