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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 - __unaligned extension inconsistent behaviour with C and C++"
href="https://bugs.llvm.org/show_bug.cgi?id=47499">47499</a>
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<th>Summary</th>
<td>__unaligned extension inconsistent behaviour with C and C++
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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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>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>rofirrim@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>struct Foo {
unsigned long x;
};
void foo(__unaligned struct Foo* out){
out->x = 5;
}
Emits this in C (which is the expected behaviour)
%struct.Foo = type { i64 }
define dso_local void @foo(%struct.Foo* nocapture %0) local_unnamed_addr #0 {
%2 = getelementptr inbounds %struct.Foo, %struct.Foo* %0, i64 0, i32 0
store i64 5, i64* %2, align 1, !tbaa !2
ret void
}
but this in C++ which does not honour the qualifier
%struct.Foo = type { i64 }
define dso_local void @_Z3fooPU11__unaligned3Foo(%struct.Foo* nocapture %0)
local_unnamed_addr #0 {
%2 = getelementptr inbounds %struct.Foo, %struct.Foo* %0, i64 0, i32 0
store i64 5, i64* %2, align 8, !tbaa !2
ret void
}
We want both languages agree. I suggest we bring the current behaviour in C to
C++.</pre>
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