[Bug c++/34459] [4.1/4.3 Regression] incorrect code when compiled with optimization (-O1)

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from jakub at gcc dot gnu dot org  2007-12-19 15:31 -------
extern void abort (void);
extern void *memset (void *s, int c, __SIZE_TYPE__ n);

struct S
{
  char s[25];
};

struct S *p;

void __attribute__((noinline))
foo (struct S *x, int set)
{
  int i;
  for (i = 0; i < sizeof (x->s); ++i)
    if (x->s[i] != 0)
      abort ();
    else if (set)
      x->s[i] = set;
  p = x;
}

int
main ()
{
  struct S a;
  memset (&a.s, '\0', sizeof (a.s));
  foo (&a, 0);
  struct S b = a;
  foo (&b, 1);
  b = a;
  b = *p;
  foo (&b, 0);
  return 0;
}

fails on the trunk too at -O2 (succeeds with -O2 -fno-tree-dse).  Here we have:
  # VUSE <aD.1560_18> { aD.1560 }
  # bD.1561_21 = VDEF <bD.1561_19> { bD.1561 }
  bD.1561 = aD.1560;
  # VUSE <pD.1547_17> { pD.1547 }
  p.2D.1562_1 = pD.1547;
  # VUSE <aD.1560_18, SMT.28D.1593_20> { aD.1560 bD.1561 SMT.28D.1593 }
  # bD.1561_22 = VDEF <bD.1561_21> { bD.1561 }
  bD.1561 = *p.2D.1562_1;
at dce4.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34459