https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99101
Bug ID: 99101
Summary: optimization bug with -ffinite-loops
Product: gcc
Version: og10 (devel/omp/gcc-10)
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: 251078896 at qq dot com
Target Milestone: ---
we have a reduced code to show this bug:
#include <iostream>
class CompactMD {
public:
void operator()() {
while (true) {
auto num_job = jobs_;
for (auto i = 0; i < jobs_; i++) SendNextMd();
jobs_ -= num_job;
}
}
void SendNextMd() {
if (at_eof_) return;
if (read_finish_) {
at_eof_ = true;
std::cout << 1 << std::endl;
}
}
bool read_finish_ = true;
int jobs_{1};
bool at_eof_{false};
};
int main() {
CompactMD comp_md_;
comp_md_();
return 0;
}
The expected output is only one line of "1", after that the program should be
in a "while true" loop forever.
With O2 optimization level, the output are infinite lines of "1"s.
We can reproduce this in RedHat's devtoolset-10, and Ubuntu 20.10's bundled
gcc10. After some tests, I find this bug is related to -ffinite-loops
This bug cannot be reproduced with gcc9 or lower version.
btw, I cannot further simplify this code for now, any change to it the bug is
likely to be gone.
