https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125345
Bug ID: 125345
Summary: [16/17 Regression] -D_GLIBCXX_ASSERTIONS with -O2
leads to abort/segfault
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gnu.ojxq8 at dralias dot com
Target Milestone: ---
Code to reproduce:
```cpp
#include <array>
struct Data {
std::array<unsigned, 8> dst;
std::array<unsigned, 8> src{1};
};
int main() {
Data d;
d.dst = d.src;
unsigned p = d.dst.size();
while (!d.dst[--p]) ;
(void)__builtin_clz(d.dst[p]);
}
```
Command to reproduce:
```
# g++-15 -O2 -std=c++11 -D_GLIBCXX_ASSERTIONS ./work.cc -o ./e && ./e
# g++-16 -O2 -std=c++11 -D_GLIBCXX_ASSERTIONS ./work.cc -o ./e && ./e
Segmentation fault (core dumped)
```
Godbolt:
https://godbolt.org/z/nMq8G78qc
While reducing the test case, I found that it sometimes goes away with -O3, but
not always. Also, when inlining the two Data fields into main directly, the
segv becomes an abort.
