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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi Renato,<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">On 5 February 2013 11:03, David Tweed <<a href="mailto:david.tweed@arm.com" target="_blank">david.tweed@arm.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">since the more instructions there<br>
are the more an out-of-order CPU can put them into otherwise unused slots. I<br>
can't think of a way of figuring out such a mapping other than empirically.<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"><span style="color:#1F497D">> </span>Given the amount of uncertainty on these OOO guesses, I don't think we can get anything worth trying, even empirically. The noise will always outweigh the signal.<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="color:#1F497D">> </span>You can normally save a few cycles on a static micro-benchmark and think you're in control, but you normally don't evaluate the exact impact that the same guess had on other benchmarks or real code.
Since this is auto-vectorization, it'll be hard to<span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">> </span> compare, but more so to evaluate the overall impact on the rest.<span style="color:#1F497D"><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">That may be the case. Just to be clear I was thinking of something incredibly simple along the lines of (cost) ^ (min(1-alpha*noOfINstructions,floorTheshold))
for some values of alpha and floorThreshold. I'll probably have a look at this when I next get some discretionary time, but that wont' be for a couple of months. Having said that, it may turn out that it doesn't really matter in that the more vector instructions
you've got the higher the likelihood it will have a lower cost than a scalar version.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">ave<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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