https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109703
Bug ID: 109703
Summary: __builtin_unreachable() reached
Product: gcc
Version: 13.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: christian.morales.vega at gmail dot com
Target Milestone: ---
This
(https://github.com/gcc-mirror/gcc/commit/bf78b43873b0b7e8f9a430df38749b8b61f9c9b8#diff-c8a656ef205ec6452ef0bed111a387dc9e7eb2404fb3222a48f9f93b2460bd55R278)
__builtin_unreachable() is reached using this code
--------------------------------------
#include <boost/algorithm/string/case_conv.hpp>
#include <string>
int main() {
auto lower = std::string{"0123456789ABCDEF"};
auto upper = boost::algorithm::to_upper_copy(lower);
}
--------------------------------------
with Boost 1.82.
Doing "g++ -O1 -fsanitize=undefined -o main main.cpp && ./main" results in
/usr/include/c++/13/bits/basic_string.h:278:29: runtime error: execution
reached an unreachable program point
This is with gcc-13.1.1-1.fc38.x86_64 from Fedora 38.
AFAICT the bug is in libstdc++.
During the first iteration, is not until
https://github.com/gcc-mirror/gcc/blob/releases/gcc-13.1.0/libstdc%2B%2B-v3/include/bits/basic_string.tcc#L201
that the data pointer is replaced from the SSO to the heap one; but one line
before, in
https://github.com/gcc-mirror/gcc/blob/releases/gcc-13.1.0/libstdc%2B%2B-v3/include/bits/basic_string.tcc#L200
https://github.com/gcc-mirror/gcc/blob/releases/gcc-13.1.0/libstdc%2B%2B-v3/include/bits/basic_string.h#L293
https://github.com/gcc-mirror/gcc/blob/releases/gcc-13.1.0/libstdc%2B%2B-v3/include/bits/basic_string.h#L275
, it checks whether it should destroy the data based on whether _M_data() ==
_M_local_data().
