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<div class="moz-cite-prefix">On 12/17/18 4:19 AM, Markus Lavin via llvm-dev wrote:<br>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black">Hello,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">I have been looking at using LazyValueInfo to improve BasicAA for some cases but have noted some issues with LVI<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black">1. The interface (e.g. getConstantRange) seem to expect pointer-to-non-const objects which is a bit troublesome if you want to use the analysis from a place where you have pointer-to-const. Resorting
to const_cast is obviously undesirable.</span></p>
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<p>There are a number of interfaces that, for historical reasons, don't take const-qualified pointers (although they probably should). For some of these we've created wrappers to hide the const_casts (e.g., in ValueTracking).<br>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black">2. Assumption patterns of the form ‘icmp <pred> (add Val, Offset)’ (<a href="https://github.com/llvm-mirror/llvm/blob/master/lib/Analysis/LazyValueInfo.cpp#L1097" moz-do-not-send="true">https://github.com/llvm-mirror/llvm/blob/master/lib/Analysis/LazyValueInfo.cpp#L1097</a>)
will not make it through the assumption cache after commit <a href="https://github.com/llvm-mirror/llvm/commit/a6e44bd6350ff4aaa40b104abff1e28a9918ef87" moz-do-not-send="true">
https://github.com/llvm-mirror/llvm/commit/a6e44bd6350ff4aaa40b104abff1e28a9918ef87</a></span></p>
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<p>Seems like an oversight (and a lack of sufficient regressions tests). Please feel free to submit a patch to fix this.
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black">Is this something worth fixing or does this mean that LVI is not very much used and there might even be plans to remove/replace it in the future?</span></p>
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<p>LVI is still very much in use (at least in JumpThreading and CorrelatedValuePropagation). I know that some people have discussed possible rewrites over the years, but I don't know of any immediate plans.<br>
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<p> -Hal<br>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">-Markus<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
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<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
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