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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86] Redundant displacement in calls to virtual base class function with this-adjustment"
href="https://llvm.org/bugs/show_bug.cgi?id=26327">26327</a>
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<th>Summary</th>
<td>[x86] Redundant displacement in calls to virtual base class function with this-adjustment
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Blocks</th>
<td>26299
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider:
struct Base1 { virtual void f1(); };
struct Base2 { virtual void f2(); };
struct S : Base1, Base2 {
void foo();
};
void S::foo() {
f2();
}
At -Os, we generate:
00000000 <?foo@S@@QAEXXZ>:
0: 8b 41 04 mov 0x4(%ecx),%eax
3: 83 c1 04 add $0x4,%ecx
6: ff 20 jmp *(%eax)
MSVC generates:
?foo@S@@QAEXXZ (public: void __thiscall S::foo(void)):
00000000: 83 C1 04 add ecx,4
00000003: 8B 01 mov eax,dword ptr [ecx]
00000005: FF 20 jmp dword ptr [eax]
saving one byte, admittedly at the cost of a longer dependency chain. Maybe
that's worth it at -Os though?</pre>
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