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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 - __builtin_sub_overflow reports invalid overflow in constexpr context"
href="https://bugs.llvm.org/show_bug.cgi?id=42000">42000</a>
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<th>Summary</th>
<td>__builtin_sub_overflow reports invalid overflow in constexpr context
</td>
</tr>
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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>FreeBSD
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Frontend
</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>m@mikaelsimonsson.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>This code fails to compile:
#include <cstdint>
constexpr bool overflows(uint8_t a, int b)
{
uint8_t diff = 0;
return __builtin_sub_overflow(a, b, &diff);
}
int main()
{
static_assert(!overflows(255, 100));
return 0;
}
11:5: error: static_assert failed due to requirement '!overflows(255, 100)'
static_assert(!overflows(255, 100));
^ ~~~~~~~~~~~~~~~~~~~~
1 error generated.
But this code compiles and runs without triggering the assert:
#include <cassert>
#include <cstdint>
inline bool overflows(uint8_t a, int b)
{
uint8_t diff = 0;
return __builtin_sub_overflow(a, b, &diff);
}
int main()
{
assert(!overflows(255, 100));
return 0;
}
Tested with godbolt.org: clang version 9.0.0 (trunk 361583)</pre>
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