Andrew Haley <[EMAIL PROTECTED]> writes: | Gabriel Dos Reis writes: | > Andrew Haley <[EMAIL PROTECTED]> writes: | > | > | Michael Veksler writes: | > | > Roberto Bagnara wrote: | > | > > | > | > > Reading the thread "Autoconf manual's coverage of signed integer | > | > > overflow & portability" I was horrified to discover about GCC's | > | > > miscompilation of the remainder expression that causes INT_MIN % -1 | > | > > to cause a SIGFPE on CPUs of the i386 family. Are there plans to | > | > > fix this bug (which, to me, looks quite serious)? | > | > > All the best, | > | > > | > | > This problem is quite rare in practice (otherwise there would be | > | > much more complaining). As such it may be too expensive, | > | > performance-wise, to fix in GCC. It seems as one of those | > | > classical things that can be worked-around in the kernel. | > | | > | I guess, or it can be fixed-up in user space. We already do this for | > | the Java language. | > | > Andrew pointed me to his implementation. | > I, however, have a question: why do we need to mess with signals at all? | > I mean, could not we generate the following for "%": | > | > rem a b := | > if abs(b) == 1 | > return 0 | > return <machine-instruction> a b | > | > is there any other corner case that will trigger the trap? | | I have tried it, and it is pretty expensive. It messes up the | pipelines and it hides the % from the optimizer.
Aha, thanks. | IMO we should not do this by default, since it's such a nitpicky | corner case. At this point, without having tried (C/C++) implementations and their effects on most software, I have no definitive opinion -- except that we do something about it. -- Gaby
