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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Understood; barriers can only be introduced in places where whenever one lane arrives all are sure to follow.<o:p></o:p></span></p>
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</span>Yes? Where is allActive defined, I couldn't find it.<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">See “Definition 12 (Static All-Active Program Point)” in subsection 5.6.11; which also provides one way of computing it, based on knowing which branches are divergent.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">This btw is analogous to LoopAccessInfo::blockNeedsPredication(); which is admittedly overly conservative due to the (current) nature of its clients.<o:p></o:p></span></p>
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<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"> Alexandre Isoard [mailto:alexandre.isoard@gmail.com]
<br>
<b>Sent:</b> Friday, July 21, 2017 18:29<br>
<b>To:</b> Zaks, Ayal <ayal.zaks@intel.com><br>
<b>Cc:</b> llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [llvm-dev] [SPIR/PTX] Divergence analysis for BasicBlocks<o:p></o:p></span></p>
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<p class="MsoNormal">My current strategy is to store all the BB in the InfluenceRegion (see the DivergencePropagator) of a divergent branch.<o:p></o:p></p>
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<p class="MsoNormal">Basically, I want an over-approximation of isControlDivergent (or an under approximation of allActive) so that I can introduce barriers, there, safely.<o:p></o:p></p>
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<p class="MsoNormal">On Fri, Jul 21, 2017 at 4:21 PM, Alexandre Isoard <<a href="mailto:alexandre.isoard@gmail.com" target="_blank">alexandre.isoard@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hello,<o:p></o:p></p>
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<p class="MsoNormal">Yes? Where is allActive defined, I couldn't find it.<o:p></o:p></p>
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<p class="MsoNormal">Basically, a BB is control divergent if it's execution depends on a branch that itself depends on a divergent ssa value.<o:p></o:p></p>
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<p class="MsoNormal">On Fri, Jul 21, 2017 at 4:13 PM, Zaks, Ayal <<a href="mailto:ayal.zaks@intel.com" target="_blank">ayal.zaks@intel.com</a>> wrote:<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">What would be the definition of “isControlDivergent(BasicBlock*)”; the complementary of “allActive(BasicBlock*)”
– blocks known to execute all lanes, whenever reached? Note the (distinct) term “rewire targets” that Ralf Karrenberg used in his thesis.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><a name="m_9107082357495268711_m_7594817159851353"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></a></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><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"> llvm-dev [mailto:<a href="mailto:llvm-dev-bounces@lists.llvm.org" target="_blank">llvm-dev-bounces@lists.llvm.org</a>]
<b>On Behalf Of </b>Alexandre Isoard via llvm-dev<br>
<b>Sent:</b> Friday, July 14, 2017 20:53<br>
<b>To:</b> llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>><br>
<b>Subject:</b> [llvm-dev] [SPIR/PTX] Divergence analysis for BasicBlocks</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hello,<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">It seems to me that our current DivergenceAnalysis does not save which BasicBlocks may suffer from divergent control. Am I correct?<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I want to modify our DivergenceAnalysis to add a "bool isControlDivergent(BasicBlock*) const" method and save in the divergence propagator the basicblock that are divergent. I am
not sure that is entirely correct, if you have input on that please let me know.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">That being said, to ease my debugging process I want to introduce a -dot-divergence pass that dump the cfg with divergent basicblocks in red. I was wondering if our dot printer
is flexible enough to allow me to also print in color the SSA variables that are divergent.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Thanks.<br clear="all">
<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b>Alexandre Isoard</b><o:p></o:p></p>
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<p class="MsoNormal"><span class="hoenzb"><span style="color:#888888">-- <o:p></o:p></span></span></p>
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<p class="MsoNormal"><b><span style="color:#888888">Alexandre Isoard</span></b><o:p></o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
<p class="MsoNormal"><b>Alexandre Isoard</b><o:p></o:p></p>
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