[BUG]: Missing GCC output with std::atomic and "compile to binary"

Describe the bug

Hi friends. I was testing the following code with x86-64 gcc 11.2 and the -O3 flag:

#include <atomic>

int f(std::atomic<int>& a) {
   return a++;
}

and f is not present in the output. https://godbolt.org/z/YdhnhhKP1

If I remove the use of std::atomic (that is, if a becomes an ordinary int), it works. https://godbolt.org/z/MbP1xofEo

If I keep std:.atomic but disable the “compile to binary flag”, it works. https://godbolt.org/z/vr1ooT3E5

Steps to reproduce

See above.

Expected behavior

The “compile to binary” should not hide information. As far as I can see, the flag’s main function is to show/hide the generated machine code. I could be wrong.

Reproduction link

See above.

Screenshots

See above.

Operating System

Windows 10

Browser version

Chrome / Firefox

[dkm]

Yes, currently CE does not support stopping after the assembler, and binary means linking to a correct executable. Stopping after assembler and be able to see relocations info was something I was willing to do in the past. I’ll look into that if there’s no urgency 😃

[dkm]

Sorry I wasn’t clear. Your initial report is not a bug and @Quuxplusone explained exactly was is happening (no main in your code, CE inserts a dummy one without any call to f, f is being removed). There’s nothing to fix in CE about this, everything is working as expected. To get your expected result, you can fix your code to have a main function that calls your f function. That’s what I did above, and that triggered a bug #3235 in the ASM parser. Fixing this bug won’t change anything to your initial code though. You can check this by simply doing it locally (copy paste your code in a file, add an empty main, run gcc -o test test.cc, disasm with objdump -d test), and you should also observe that f is missing.

Another solution will be available when https://github.com/compiler-explorer/compiler-explorer/pull/3232 is ready.