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<body><span class="vcard"><a class="email" href="mailto:timurrrr@google.com" title="Timur Iskhodzhanov <timurrrr@google.com>"> <span class="fn">Timur Iskhodzhanov</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - VS2013 CL doesn't generate a vtordisp thunk"
href="http://llvm.org/bugs/show_bug.cgi?id=20477">bug 20477</a>
<br>
<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>ASSIGNED
</td>
<td>RESOLVED
</td>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>INVALID
</td>
</tr>
<tr>
<td style="text-align:right;">Summary</td>
<td>MS ABI: clang generates unnecessary vtordisp adjustment
</td>
<td>VS2013 CL doesn't generate a vtordisp thunk
</td>
</tr></table>
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<div>
<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - VS2013 CL doesn't generate a vtordisp thunk"
href="http://llvm.org/bugs/show_bug.cgi?id=20477#c3">Comment # 3</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - VS2013 CL doesn't generate a vtordisp thunk"
href="http://llvm.org/bugs/show_bug.cgi?id=20477">bug 20477</a>
from <span class="vcard"><a class="email" href="mailto:timurrrr@google.com" title="Timur Iskhodzhanov <timurrrr@google.com>"> <span class="fn">Timur Iskhodzhanov</span></a>
</span></b>
<pre>OK, at first I thought that CL made an "no vtordisp needed" optimization based
on the fact that the B ctor is trivial.
However, this turned out not to be the case -- in fact, it's a miscompile by
CL.
This code built with VS2013 CL:
--------------------------------
#include <stdio.h>
struct A {
virtual A *f() { return this; }
};
struct B : virtual A {
B() {}
virtual B *f() { return this; }
int x;
};
void foo(B *b) {
B *bb = b->f();
printf("bb->x = %d (should be 42)\n", bb->x);
}
struct C : B {
C() {
x = 42;
foo(this);
}
};
struct D {
virtual void g() {};
};
struct E : virtual D {};
struct F : E, C, virtual D, virtual A {};
int main() {
F f;
foo(&f);
}
--------------------------------
prints out
bb->x = 17355152 (should be 42)
bb->x = 42 (should be 42)
[ <a href="https://connect.microsoft.com/VisualStudio/feedbackdetail/view/940530">https://connect.microsoft.com/VisualStudio/feedbackdetail/view/940530</a> ]
Clang did the right thing and the result works correct.</pre>
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