Re: [PATCH, MPX, 2/X] Pointers Checker [7/25] Suppress BUILT_IN_CHKP_ARG_BND optimizations.

[Ilya Enkovich <enkovich dot gnu at gmail dot com>]

2013/11/5 Richard Biener <richard.guenther@gmail.com>:
> On Tue, Nov 5, 2013 at 1:52 PM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>>
>> For input parameter P I need to have
>>   BOUNDS = __builtin_arg_bnd (P)
>> to somehow refer to bounds of P in GIMPLE.  Optimizations may modify
>> __builtin_arg_bnd (P) replacing P with its copy or some value. It
>> makes call useless because removes information about parameter whose
>> bounds we refer to. I want such optimization to ignore
>> __builtin_arg_bnd calls and always leave default SSA_NAME of PARM_DECL
>> there as arg.
>
> How does a compilable testcase look like that shows how the default def
> is used?  And what transforms break that use?  I really cannot see
> how this would happen (and you didn't add a testcase).

Here is a test source:

extern int bar1 (int *p);
extern int bar2 (int);

int foo (int *p)
{
  if (!p)
    return bar1 (p);
  return bar2 (10);
}

After instrumentation GIMPLE looks like:

foo (int * p)
{
  <unnamed type> __bound_tmp.0;
  int _1;
  int _6;
  int _8;

  <bb 6>:
  __bound_tmp.0_9 = __builtin_ia32_arg_bnd (p_3(D));

  <bb 2>:
  if (p_3(D) == 0B)
    goto <bb 3>;
  else
    goto <bb 4>;

  <bb 3>:
  _6 = bar1 (p_3(D), __bound_tmp.0_9);
  goto <bb 5>;

  <bb 4>:
  _8 = bar2 (10);

  <bb 5>:
  # _1 = PHI <_6(3), _8(4)>
  return _1;

}

Here is optimized GIMPLE (if I do not apply my changes in tree-ssa-dom.c):

foo (int * p)
{
  <unnamed type> __bound_tmp.0;
  int _1;
  int _6;
  int _8;

  <bb 2>:
  if (p_3(D) == 0B)
    goto <bb 3>;
  else
    goto <bb 4>;

  <bb 3>:
  __bound_tmp.0_9 = __builtin_ia32_arg_bnd (0B); [return slot optimization]
  _6 = bar1 (0B, __bound_tmp.0_9); [tail call]
  goto <bb 5>;

  <bb 4>:
  _8 = bar2 (10); [tail call]

  <bb 5>:
  # _1 = PHI <_6(3), _8(4)>
  return _1;

}

Now during expand or inline of foo I cannot determine the value for
__bound_tmp.0_9.

Ilya
>
> Richard.
>