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<p class="MsoNormal">This is better suited to llvm-dev, so I'm directing it there.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">llvm-commits <llvm-commits-bounces@lists.llvm.org> on behalf of Qing Shan Zhang via llvm-commits <llvm-commits@lists.llvm.org><br>
<b>Reply-To: </b>Qing Shan Zhang <qshanz@cn.ibm.com><br>
<b>Date: </b>Sunday, August 19, 2018 at 10:10 PM<br>
<b>To: </b>"llvm-commits@lists.llvm.org" <llvm-commits@lists.llvm.org><br>
<b>Subject: </b>A question about the widely used "xxx | true" inside llvm<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.0pt;font-family:"Verdana",serif">Hi, guys,<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.0pt;font-family:"Verdana",serif">I notice that, we are widely using the statement "xxx | true" in llvm, such as "return SimplifyCFG(BB) | true;". I have no idea if there is any downside
to use the logic operator "||" here. Instead, I indeed see the potential problem to use bitwise operator "|". Because the bitwise operator do not short-circuit and the language std didn't specify the evaluation order for its lhs and rhs expression. That means,
compiler is free to optimize this statement to "return true". <o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.0pt;font-family:"Verdana",serif"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.0pt;font-family:"Verdana",serif">In shorts, IMO, it is legal to do the following optimization:<br>
bool bar() {<br>
return foo() | true;<br>
}<br>
--><br>
bool bar() {<br>
return true; // the call to foo() is missing.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.0pt;font-family:"Verdana",serif">}<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.0pt;font-family:"Verdana",serif"> <br>
Best regards<br>
<br>
steven.zhang(</span><span style="font-size:10.0pt;font-family:"PMingLiU",serif">张</span><span style="font-size:10.0pt;font-family:"MS Mincho"">青山</span><span style="font-size:10.0pt;font-family:"Verdana",serif">)<br>
XLC++ Compiler Frontend Developer<br>
<br>
IBM China Development Lab, Shanghai <br>
Tel: (8621)609-28454 Mobile: +8615900986116<br>
E-mail: <a href="mailto:qshanz@cn.ibm.com">qshanz@cn.ibm.com</a><br>
</span><span style="font-size:10.0pt;font-family:"MS Mincho"">关注</span><span style="font-size:10.0pt;font-family:"Verdana",serif">IBM</span><span style="font-size:10.0pt;font-family:"MS Mincho"">中国</span><span style="font-size:10.0pt;font-family:"PMingLiU",serif">编译</span><span style="font-size:10.0pt;font-family:"MS Mincho"">器开</span><span style="font-size:10.0pt;font-family:"PMingLiU",serif">发团队</span><span style="font-size:10.0pt;font-family:"Verdana",serif">
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<br>
"All things are difficult before they are easy."<o:p></o:p></span></p>
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<o:p></o:p></p>
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