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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#1F497D">Hi
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">mbraun<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Thanks for your information.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">What about following situation:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">3)
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">OP_X …, implicit-def dead %X
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">with<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">OP_X …, implicit-def dead %X<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Between two instructions, there may be another instruction(not OP_X) which also def %X,
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Is it correct to do CSE in this situation?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Best wishes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Michael<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> mbraun@apple.com [mailto:mbraun@apple.com]
<br>
<b>Sent:</b> Monday, October 22, 2018 5:51 AM<br>
<b>To:</b> Matthias Braun <mbraun@apple.com><br>
<b>Cc:</b> Yuchao (Michael) <michael.yuchao@huawei.com>; llvm-dev@lists.llvm.org; sunqiang (I) <sunqiang13@huawei.com><br>
<b>Subject:</b> Re: [llvm-dev] Question about MachineCSE optimization<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal"><span lang="EN-US"><br>
<br>
<o:p></o:p></span></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
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<p class="MsoNormal"><span lang="EN-US">On Oct 21, 2018, at 2:48 PM, mbraun via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">As far as I understand it (though I didn’t write the code so I may be missing something) this is about making sure liveness flags (kill, dead) are updated correctly when merging instruction. The situations to consider
are probably:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">1)<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-US">OP_X …, implicit-def %X<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">with<o:p></o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-US">OP_X …, implicit-def dead %X<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">The merged instruction probably should not have a dead flag set. The 2nd if appears to be about this situation:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">2)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">OP_X …, implicit-def dead %X<o:p></o:p></span></p>
</div>
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<p class="MsoNormal"><span lang="EN-US">Use killed %X<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">…<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">OP_X …, implicit-def %X ; this gets merged with the previous OP_X<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Use %X<o:p></o:p></span></p>
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</blockquote>
<div>
<p class="MsoNormal"><span lang="EN-US">This example should of course read:<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">OP_X …, implicit-def %X<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">Use killed %X<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">…<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">OP_X …, implicit-def %X ; this gets merged with the previous OP_X<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">Use %X<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-US">Once we merge the 2nd OP_X with the first one, we have to drop the `killed` flags on all users of %X between the first OP_X and the position where we had the 2nd OP_X before it was merged.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><br>
<br>
<o:p></o:p></span></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
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<div>
<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Once we merge the 2nd OP_X with the first one, we have to drop the `killed` flags on the %X users.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Though admittedly I am at a loss right now why this is only performed for implicit operands and not for all operands…<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">- Matthias<o:p></o:p></span></p>
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<div>
<div>
<p class="MsoNormal"><span lang="EN-US"><br>
<br>
<o:p></o:p></span></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal"><span lang="EN-US">On Oct 20, 2018, at 1:38 AM, Yuchao (Michael) via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">Hi<span class="apple-converted-space"> </span><o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">I am trying to fix a bug in MachineCSE and have one question about following code:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">*********************************************<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">// Go through implicit defs of CSMI and MI, if a def is not dead at MI,<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">// we should make sure it is not dead at CSMI.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">if (MO.isImplicit() && !MO.isDead() && CSMI->getOperand(i).isDead())<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> ImplicitDefsToUpdate.push_back(i);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">// Keep track of implicit defs of CSMI and MI, to clear possibly<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">// made-redundant kill flags.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">if (MO.isImplicit() && !MO.isDead() && OldReg == NewReg)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> ImplicitDefs.push_back(OldReg);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">if (OldReg == NewReg) {<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> --NumDefs;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> continue;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">}<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">**********************************************<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">From Above source code, it seems that CSE does not handle instruction which<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">have one operand that is ‘implicit+isDead+isDef’.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">Base on my understanding, implicit dead register is mean clobbered, so it is not safe to<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">do CSE. Is this right?<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">Best wishes<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif">Michael<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify;text-justify:inter-ideograph"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:9.0pt;font-family:"Helvetica",sans-serif">_______________________________________________<br>
LLVM Developers mailing list<br>
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</span><span lang="EN-US"><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev"><span style="font-size:9.0pt;font-family:"Helvetica",sans-serif;color:#954F72">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</span></a><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">_______________________________________________<br>
LLVM Developers mailing list<br>
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<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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