Optimizer optimizes out potential infinite loop

[Pranavkumar-T-S]

All information necessary to reproduce the problem.

It is reproducible in

• version: clang 18 and above
• architecture: x86_64, armv8-a, arv7-a
• optimization flag : O1 and above
• standard : c++11 and above

The reduced test-case that triggers the bug.

#include <iostream>
#include <unordered_set>
int main() {
    std::unordered_set<int> isPresent;
    isPresent.insert(0);
    // std::cout << "before loop, size of isPresent: " << isPresent.size() << std::endl;
    while (!isPresent.empty()) {
        // std::cout << "infinite loop " << std::endl;
    };
    // std::cout << "after loop " << std::endl;

    return 0;
}

The location where you obtained LLVM (if not from our Git repository).

• it is from compiler explorer.

[topperc]

By default clang assumes loops that don't do anything with terminate. You can disable this with -fno-finite-loops