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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - integer truncation error in areStridedAccessesIndependent"
href="https://llvm.org/bugs/show_bug.cgi?id=28443">28443</a>
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<th>Summary</th>
<td>integer truncation error in areStridedAccessesIndependent
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>3.8
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>FreeBSD
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>cperciva@freebsd.org
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=16701" name="attach_16701" title="Test case; crashes clang38 -O2">attachment 16701</a> <a href="attachment.cgi?id=16701&action=edit" title="Test case; crashes clang38 -O2">[details]</a></span>
Test case; crashes clang38 -O2
The attached reduced test case crashes clang38 -c -O2 on my FreeBSD/amd64
system:
Assertion failed: (Distance > 0 && "The distance must be non-zero"), function
areStridedAccessesIndependent, file
/wrkdirs/usr/ports/devel/llvm38/work/llvm-3.8.0.src/lib/Analysis/LoopAccessAnalysis.cpp,
line 1004.
This is because the function areStridedAccessIndependent takes "unsigned"
values
static bool areStridedAccessesIndependent(unsigned Distance, unsigned Stride,
unsigned TypeByteSize)
where it should be taking target size_t values: I am compiling for a 64-bit
platform, and the distance between memory accesses is 2^32 bytes, but the
"unsigned" type is a 32-bit integer so 2^32 gets truncated to 0.
In addition to causing a crash when the distance between memory accesses is a
multiple of 2^32 bytes, this bug could theoretically cause incorrect code
generation, e.g., if the distance is 2^32+2 bytes and the stride length is
2^31+1; using 32-bit integers it appears that the distance is not a multiple of
the stride length, and invalid optimizations may occur.</pre>
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