Re: Miscompilation of remainder expressions

[Gabriel Dos Reis <gdr at cs dot tamu dot edu>]

Andrew Haley <aph@redhat.com> 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?


-- Gaby