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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 - Wrong evaluation of constexpr function with loop"
href="https://bugs.llvm.org/show_bug.cgi?id=37174">37174</a>
</td>
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<tr>
<th>Summary</th>
<td>Wrong evaluation of constexpr function with loop
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>morandidodo@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The following code does not compile with the trunk version (tested on godbolt
with the arguments: -std=c++17 -Wall -Wextra
--gcc-toolchain=/opt/compiler-explorer/gcc-snapshot)
#include <array>
template <typename Iter>
constexpr Iter
fun(Iter first, Iter last, Iter elem) {
typename std::iterator_traits<Iter>::difference_type index = 1;
for(auto iter = std::next(first); iter < last; /* missing increment here!
*/) {
auto nextIter = std::next(iter, index + 1);
if (iter >= last)
return last;
++index;
iter = nextIter;
}
return last;
}
constexpr bool
test() {
std::array data {0, 1, 2, 3};
return fun(std::begin(data), std::end(data), std::next(std::begin(data),
2)) <= std::end(data);
}
static_assert(test());
I am not sure if the code could be simplified more than this to cause the bug.</pre>
</div>
</p>
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