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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - False negative analyse c++ code in asserts"
href="https://bugs.llvm.org/show_bug.cgi?id=46238">46238</a>
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<th>Summary</th>
<td>False negative analyse c++ code in asserts
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>10.0
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<th>Hardware</th>
<td>Macintosh
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<th>OS</th>
<td>MacOS X
</td>
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>spider.ch@gmail.com
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
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<pre>Hello.
I found an issue with warnings and asserts.
Let's say we have code:
#include <cassert>
enum class State
{
A = 0,
B,
C,
D,
E,
F
};
void ProcessState(State s)
{
assert(s > State::A || s < State::E); // < No warning
(__builtin_expect(!(s > State::A || s < State::E), 0) ?
__assert_rtn(__func__, "main.cpp", 15, "s > State::A || s < State::E") :
(void)0); // < main.cpp:16:38: warning: overlapping comparisons always evaluate
to true [-Wtautological-overlap-compare]
if (s > State::A || s < State::E) // < main.cpp:17:22: warning:
overlapping comparisons always evaluate to true
[-Wtautological-overlap-compare]
void(0);
}
int main(int, char**)
{
ProcessState(State::B);
return 0;
}
And compile code with:
clang++ -std=c++17 -g -O1 -Wtautological-compare main.cpp -o test
There will be no warning on line 15, but there is a mistake. If we move code
from assert to if or change assert with preprocessed code (as in line 16) then
a warning appears.
This behavior was seen in clang 5.0(Maybe and earlier, but I didn't check) and
later.</pre>
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