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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - instcombine incorrectly removes "dead" malloc/operator delete pair"
href="https://bugs.llvm.org/show_bug.cgi?id=41039">41039</a>
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<th>Summary</th>
<td>instcombine incorrectly removes "dead" malloc/operator delete pair
</td>
</tr>
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<th>Product</th>
<td>libraries
</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>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>efriedma@quicinc.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
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<pre>Testcase:
#include <cstddef>
#include <cstdio>
#include <cstdlib>
void* operator new(size_t sz) {
printf("Calling new\n");
return malloc(sz);
}
__attribute__((noinline))
void operator delete(void* ptr) noexcept {
printf("Calling delete\n");
return free(ptr);
}
int* f() { return new int; }
int main() { delete f(); }
With "clang -O2", outputs "Calling new", but not "Calling delete". I think
this is a bug according to the standard: we're allowed to remove dead
new/delete pairs, but we have to either remove a complete pair, or nothing at
all.
I think this is a bug in instcombine, that it considers any pair of
allocation/deallocation function to be dead, even if that pair is something
like malloc/operator delete.</pre>
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