[Bug tree-optimization/19828] [4.0 Regression] LIM is pulling out a pure function even though there is something which can modify global memory

jakub at gcc dot gnu dot org gcc-bugzilla@gcc.gnu.org
Fri Feb 18 21:16:00 GMT 2005


------- Additional Comments From jakub at gcc dot gnu dot org  2005-02-18 15:55 -------
Just got hit by this too on subversion.
Distilled testcase is:
typedef __SIZE_TYPE__ size_t;
extern size_t strlen (const char *s);
extern int strncmp (const char *s1, const char *s2, size_t n);
extern void abort (void);

const char *a[16] = { "a", "bc", "de", "fgh" };

int
foo (char *x, const char *y, size_t n)
{
  size_t i, j = 0;
  for (i = 0; i < n; i++)
    {
      if (strncmp (x + j, a[i], strlen (a[i])) != 0)
        return 2;
      j += strlen (a[i]);
      if (y)
        j += strlen (y);
    }
  return 0;
}

int
main (void)
{
  if (foo ("abcde", (const char *) 0, 3) != 0)
    abort ();
  return 0;
}

With Zdenek's definition of pure the only pure functions in builtins.def
would be is*/to*, none of the string/memory functions could be.  But the
documentation explicitely mentions strlen and memcmp as pure functions.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19828



More information about the Gcc-bugs mailing list