[Bug target/30484] New: Miscompilation of remainder expressions on CPUs of the i386 family

["bagnara at cs dot unipr dot it" <gcc-bugzilla at gcc dot gnu dot org>]

The program below shows (at all the optimization levels) a miscompilation of
the remainder expression that causes INT_MIN % -1 to cause a SIGFPE on CPUs of
the i386 family.

#include <limits.h>
#include <stdio.h>

int minus_one(int n) {
  return (n+1)*(n-1)-n*n;
}

void p(int x, int y) {
  int z = x % y;
  printf("%d %% %d -> %d\n", x, y, z);
}

int main(int argc, char** argv) {
  p(INT_MIN, minus_one(argc));
}

For simpler programs, the behavior depends on the ability of the optimizer to
realize that the divisor is -1, in which case the compiler evaluates the
remainder expression (to 0, at compile-time) and no signal is raised.

Since the remainder is always defined, this violates the C standard.

By the way, the Ariane 5 Flight 501 crash was caused by an unexpected exception
(http://en.wikipedia.org/wiki/Ariane_5_Flight_501).


-- 
           Summary: Miscompilation of remainder expressions on CPUs of the
                    i386 family
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bagnara at cs dot unipr dot it


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30484