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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - False positive, 32-bit access from a 64-bit initialized value"
href="https://bugs.llvm.org/show_bug.cgi?id=47727">47727</a>
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<th>Summary</th>
<td>False positive, 32-bit access from a 64-bit initialized value
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>11.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>other
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Static Analyzer
</td>
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<th>Assignee</th>
<td>dcoughlin@apple.com
</td>
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<th>Reporter</th>
<td>eblot.ml@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dcoughlin@apple.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Using LLVM/clang 11.0.0-rc3 static analyzer.
The following snippets should, I believe, run ok with the static analyzer.
void foo1(uint32_t * out) {
uint64_t tmp64;
tmp64 = 0;
uint32_t * tmp32 = (uint32_t *)&tmp64;
*out = tmp32[1];
}
void foo2(uint32_t * out) {
uint64_t tmp64[1];
tmp64[0] = 0;
uint32_t * tmp32 = (uint32_t *)tmp64;
*out = tmp32[1];
}
void foo3(uint32_t * out) {
uint64_t tmp64[1];
memset(tmp64, 0, sizeof(tmp64));
uint32_t * tmp32 = (uint32_t *)tmp64;
*out = tmp32[1];
}
However, `foo2` is signalled with
warning: Assigned value is garbage or undefined
*out = tmp32[1];
^ ~~~~~~~~
1 warning generated.
On 32-bit target, both upper and lower 32-bit location of tmp64 are initialized
to 0, so these locations do not contain garbage.
They all generate the same ASM code (RISC-V 32 bit target, -O0)</pre>
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