[Bug rtl-optimization/41239] New: Scheduler reorders division by zero before a call that might not return

[jakub at gcc dot gnu dot org]

This testcase distilled from postgresql fails at runtime on s390x-linux with
-O2 -march=z9-109 -mtune=z10:

/* { dg-do run } */
/* { dg-options "-O2" } */
/* { dg-options "-O2 -march=z9-109 -mtune=z10" { target s390x-linux } } */

struct S
{
  short nargs;
  unsigned long arg[2];
};

extern void abort (void);
extern void exit (int);
extern char errstart (int, const char *, int, const char *, const char *);
extern void errfinish (int, ...);
extern int errcode (int);
extern int errmsg (const char *fmt, ...) __attribute__ ((format (printf, 1,
2)));

unsigned long
test (struct S *x)
{
  signed int arg1 = x->arg[0];
  long int arg2 = x->arg[1];

  if (arg2 == 0)
    (errstart (20, "int8.c", 924, __func__, ((void *) 0))
     ? (errfinish (errcode (0x2040082), errmsg ("division by zero")))
     : (void) 0);

  return (long int) arg1 / arg2;
}

int
main (void)
{
  struct S s = { 2, { 5, 0 } };
  test (&s);
  abort ();
}

__attribute__((noinline)) char
errstart (int x, const char *y, int z, const char *w, const char *v)
{
  asm volatile ("" : "+r" (x) : "r" (y), "r" (z), "r" (w), "r" (v) : "memory");
  return x;
}

__attribute__((noinline)) int
errcode (int x)
{
  asm volatile ("" : "+r" (x) : : "memory");
  return x;
}

__attribute__((noinline)) int
errmsg (const char *x, ...)
{
  asm volatile ("" : "+r" (x) : : "memory");
  return *x;
}

__attribute__((noinline)) void
errfinish (int x, ...)
{
  asm volatile ("" : "+r" (x) : : "memory");
  if (x)
    /* Could be a longjmp or throw too.  */
    exit (0);
}

The problem is that 2nd scheduler pass reorders the division before some of the
calls.  If the calls were guaranteed to return, that would be fine, the program
would crash sooner or later, but as shown in the testcase the call can not
return (exit, longjmp, throw) and in that case whether the division is
scheduled before or after the call matters.


-- 
           Summary: Scheduler reorders division by zero before a call that
                    might not return
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: s390x-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41239