[Bug tree-optimization/43784] [4.6 Regression] -Os -fkeep-inline-functions causes FAIL: gcc.c-torture/execute/builtins/pr22237.c execution

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2010-07-23 11:20 -------
Confirmed.  But I think this might trigger undefined behavior according to
the C standard as you are doing

  v.e.b = v.d.b;

which has overlapping lhs/rhs.  And we end up with

rp:
.LFB0:
        .cfi_startproc
        movq    %rdi, %rax
        movl    $v, %esi
        movl    $64, %ecx
        rep movsl
        ret
        .cfi_endproc

compared to 4.5 we end up with return slot optimization for the call to rp().

Testcase that also reproduces with -O[123]:

struct s {
  unsigned char a[256];
};
union u {
  struct { struct s b; int c; } d;
  struct { int c; struct s b; } e;
};

static union u v;
static struct s *p = &v.d.b;
static struct s *q = &v.e.b;

static struct s __attribute__((noinline)) rp(void)
{
  return *p;
}

static void qp(void)
{
  *q = rp();
}

int main()
{
  int i;
  for (i = 0; i < 256; i++)
    p->a[i] = i;
  qp();
  for (i = 0; i < 256; i++)
    if (q->a[i] != i)
      __builtin_abort();
  return 0;
}


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Priority|P3                          |P1
   Last reconfirmed|0000-00-00 00:00:00         |2010-07-23 11:20:14
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43784