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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - InstSimplify incorrectly folds signed comparisons of 'gep inbounds'"
href="https://bugs.llvm.org/show_bug.cgi?id=52429">52429</a>
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<th>Summary</th>
<td>InstSimplify incorrectly folds signed comparisons of 'gep inbounds'
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Keywords</th>
<td>miscompilation
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<th>Severity</th>
<td>normal
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>nunoplopes@sapo.pt
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<th>CC</th>
<td>lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org, regehr@cs.utah.edu, sanjoy@playingwithpointers.com
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<pre>File: Transforms/InstSimplify/compare.ll
define i1 @gep_same_base_constant_indices(i8* %a) {
; CHECK-NEXT: ret i1 true
;
%arrayidx1 = getelementptr inbounds i8, i8* %a, i64 1
%arrayidx2 = getelementptr inbounds i8, i8* %a, i64 10
%cmp = icmp slt i8* %arrayidx1, %arrayidx2
ret i1 %cmp
}
Folding such unsigned comparisons is correct, but not for signed as an object
may cross the unsigned/signed line, e.g:
ptr = malloc(42) // 0x7fff..ff0
ptr + 42 // 0x8....</pre>
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