https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120747
--- Comment #17 from Filip Kastl <pheeck at gcc dot gnu.org> --- (In reply to Andrew Pinski from comment #15) > So it looks like (a * b) are closer in value to (vnb12 * 1.2e+1 - c) than > (vnb12 * 1.2e+1) is to (a * b - c) . Btw, for the purpose of me trying to get better at debugging similar things, how did you figure this out? Did you perhaps run gromacs in a debugger and looked at what values those variables usually have? Or did you figure this out from gromacs' source files?