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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Possible Issue with Whole Program Devirtualization"
href="https://bugs.llvm.org/show_bug.cgi?id=50190">50190</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Possible Issue with Whole Program Devirtualization
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>steplong@quicinc.com
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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</tr></table>
<p>
<div>
<pre>class A {
public:
virtual int foo() const = 0;
};
class B : public A {
public:
virtual int foo() const { return 2; }
};
class C : public A {
public:
virtual int foo() const { return 3; }
};
A *get_A(int num) {
if (num > 1) {
printf("returning new B\n");
return new B;
}
printf("returning new C\n");
return new C;
}
__attribute__((noinline))
void call_foo(int argc) {
C *c = (C *)get_A(argc);
printf("%d\n", c->foo());
}
int main(int argc, char *argv[]) {
call_foo(argc);
}
trunk clang with -O3 -flto -whole-program-vtables -fvisibility=hidden outputs
./a.out 1
returning new B
3
gcc 10.2 with -O3 -flto -fwhole-program -fvisibility=hidden outputs
./a.out 1
returning new B
2
It looks like the c->foo is being devirtualized to a direct C::foo() call.</pre>
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</p>
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