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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - accept-invalid: __builtin_types_compatible_p pollutes the environment of tag type checking"
href="https://bugs.llvm.org/show_bug.cgi?id=49337">49337</a>
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<th>Summary</th>
<td>accept-invalid: __builtin_types_compatible_p pollutes the environment of tag type checking
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<th>Product</th>
<td>clang
</td>
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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
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>-New Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>zhan3299@purdue.edu
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>I am not sure how to accurately describe the problem. In short,
Following code is obviously invalid, as the use of 'X' with tag type does not
match previous declaration (<a href="https://godbolt.org/z/qad8vz">https://godbolt.org/z/qad8vz</a>).
$ cat case1.c
struct X {
union X {
int b;
long c;
} d;
} a;
int main() { return 0; }
However, when we put this erroneous declaration into a
__builtin_types_compatible_p function, clang accepts it
(<a href="https://godbolt.org/z/TrxTzs">https://godbolt.org/z/TrxTzs</a>). Note that it is rejected by GCC
(<a href="https://godbolt.org/z/rWde88">https://godbolt.org/z/rWde88</a>).
$ cat case2.c
int main() {
int a = __builtin_types_compatible_p(int, struct X {
union X {
int b;
long c;
} d;
});
return a;
}
Even worse, this invalid __builtin_types_compatible_p may additionally affects
other statements (<a href="https://godbolt.org/z/avxvzj">https://godbolt.org/z/avxvzj</a>), which, at least, gives the
wrong error reports.
$ cat case3.c
int main() {
int a = __builtin_types_compatible_p(int, struct X {
union X {
int b;
long c;
} d;
});
enum X { A, B } h;
h = A;
return a;
}
$ clang case3.c
#1 with x86-64 clang (trunk)
case3.c:10:9: error: use of undeclared identifier 'A'
h = A;
^
1 error generated.</pre>
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