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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - calloc() overflow test eliminated by optimization"
href="https://bugs.llvm.org/show_bug.cgi?id=37304">37304</a>
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<th>Summary</th>
<td>calloc() overflow test eliminated by optimization
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>6.0
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>wellons@nullprogram.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Minimal example:
#include <stdint.h>
#include <stdlib.h>
int test_calloc(void) {
return !!calloc(SIZE_MAX, 2);
}
With -O1:
define i32 @test_calloc() local_unnamed_addr #0 {
ret i32 1
}
The calloc() is eliminated because the returned pointer is unused. It's
replaced by a simulated successful return despite the allocation being
impossible, at least on the targeted platforms. In a more complicated scenario,
a later part of the function — such an uneliminated malloc() of the same
allocation size — may rely on calloc()'s overflow test for correct results.
A contrived example of this:
void *test_overflow(size_t n, size_t m) {
return calloc(n, m) ? malloc(n * m) : 0;
}
Compiles to:
define noalias i8* @test_overflow(i64, i64) local_unnamed_addr #0 {
%3 = mul i64 %1, %0
%4 = tail call noalias i8* @malloc(i64 %3) #2
ret i8* %4
}
An eliminated calloc() should be replaced by an overflow test.</pre>
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