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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 --- - clang does not devirtualize method pointer calls against final classes when method identity is known at compile time"
href="https://llvm.org/bugs/show_bug.cgi?id=27096">27096</a>
</td>
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<th>Summary</th>
<td>clang does not devirtualize method pointer calls against final classes when method identity is known at compile time
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Keywords</th>
<td>code-quality
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hlandau@devever.net
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>// Example:
struct Foo final {
virtual int bar();
};
int a(Foo &f, int (Foo::*fp)()) {
return (f.*fp)();
}
int b(Foo &f) {
return a(f, &Foo::bar);
}
// Generated assembly:
b(Foo&): # @b(Foo&)
mov rax, qword ptr [rdi]
jmp qword ptr [rax] # TAILCALL
// Expected assembly:
b(Foo&): # @b(Foo&)
jmp Foo::bar() # TAILCALL
// Generates expected assembly:
int c(Foo &f) {
return f.bar();
}
// This is the assembly for a, which generates a more conservative
// method pointer call, demonstrating that the knowledge about the identity of
// fp when inlining in b is definitely used to generate the code above.
// Yet the devirtualization which could be taken as a further step above does
not occur.
a(Foo&, int (Foo::*)()): # @a(Foo&, int (Foo::*)())
add rdi, rdx
test sil, 1
je .LBB0_2
mov rax, qword ptr [rdi]
mov rsi, qword ptr [rsi + rax - 1]
.LBB0_2:
jmp rsi # TAILCALL</pre>
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