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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 - -Wconditional-uninitialized false positive on struct array field"
href="https://bugs.llvm.org/show_bug.cgi?id=38856">38856</a>
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</tr>
<tr>
<th>Summary</th>
<td>-Wconditional-uninitialized false positive on struct array field
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Static Analyzer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dcoughlin@apple.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>evan.j.pretti@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=20850" name="attach_20850" title="test.c">attachment 20850</a> <a href="attachment.cgi?id=20850&action=edit" title="test.c">[details]</a></span>
test.c
I have attached a case highlighting some strange behavior regarding
-Wconditional-uninitialized.
----- test.c -----
#include <stdio.h>
typedef struct { int x[2]; } test_t;
test_t foo_1(void);
test_t foo_2(void);
test_t foo_3(void);
test_t foo_1() {
test_t t;
for(int i = 0; i < 2; i++) t.x[i] = 0;
return t;
}
test_t foo_2() {
test_t t;
t.x[0] = 0;
for(int i = 0; i < 2; i++) t.x[i] = 0;
return t;
}
test_t foo_3() {
test_t t;
t.x[0] = 0;
return t;
}
int main() {
test_t t;
t = foo_1();
printf("%i %i\n", t.x[0], t.x[1]);
t = foo_2();
printf("%i %i\n", t.x[0], t.x[1]);
t = foo_3();
printf("%i %i\n", t.x[0], t.x[1]);
}
------------------
Compilation gives:
------------------
$ clang -Weverything test.c
test.c:12:12: warning: variable 't' may be uninitialized when used here
[-Wconditional-uninitialized]
return t;
^
test.c:10:5: note: variable 't' is declared here
test_t t;
^
1 warning generated.
------------------
although both elements of the array in the struct test_t have been assigned in
foo_1() where the warning is coming from. Manual assignment of the elements
without a loop gives no warnings. Strangely, if the first element is set as in
foo_2() followed by the loop, there is no warning.
This is fine if false positives from -Wconditional-uninitialized are considered
to be acceptable. However, in foo_3(), only the first element of the array is
set and there are no warnings; the second element is actually uninitialized.
This seems like it shouldn't happen. Is this valid/wontfix behavior or a real
problem?</pre>
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