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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - LVI should understand conditional branches where the condition is a conjunction or disjunction"
href="https://llvm.org/bugs/show_bug.cgi?id=27296">27296</a>
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<th>Summary</th>
<td>LVI should understand conditional branches where the condition is a conjunction or disjunction
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>regehr@cs.utah.edu
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>LVI is perfectly capable of learning from sequenced simple branches:
%cmp = icmp sgt i32 %x, 20
br i1 %cmp, label %cont, label %if.end3
%cmp1 = icmp sgt i32 %y, 200
br i1 %cmp1, label %if.then2, label %if.end3
%add = add nsw i32 %y, %x
However, after SimplifyCFG we're instead looking at code like this:
%cmp = icmp sgt i32 %x, 20
%cmp1 = icmp sgt i32 %y, 200
%or.cond = and i1 %cmp, %cmp1
br i1 %or.cond, label %if.then2, label %if.end3
And now LVI learns nothing. A mix would be to cause LVI to look for cases where
an i1 that goes to a branch is the result of an and, and recursively accumulate
dataflow facts.
Though it's probably less important, LVI can also learn facts when flags are
or'ed, for example:
%cmp = icmp eq i32 %x, 10
%cmp1 = icmp eq i32 %x, 12
%or.cond = or i1 %cmp, %cmp1
br i1 %or.cond, label %if.then2, label %if.end3</pre>
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