[Bug tree-optimization/24169] New: Address (full struct) escapes even though the called function does not cause it to escape

[Bug tree-optimization/24169] New: Address (full struct) escapes even though the called function does not cause it to escape

[pinskia at gcc dot gnu dot org]

Just like PR 23134, here is another testcase for the aliasing thinking that the
address escapes but this time it has SFT's involved and we should not have a
V_MAY_DEF for k.i:
static void f(char *a)
{
  *a = 1;
}

struct g
{
  char i, j;
};

void h(void)
{
  struct g k = {2, 2};
  f(&k.j);
  if (k.i != 2)
    link_error ();
}

Compile with -O2 -fno-inline to force f not to inline.


-- 
           Summary: Address (full struct) escapes even though the called
                    function does not cause it to escape
           Product: gcc
           Version: 4.1.0
            Status: NEW
          Keywords: missed-optimization, alias
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24169

[Bug tree-optimization/24169] Address (full struct) escapes even though the called function does not cause it to escape

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-01-01 00:41 -------
Just a clarification here, I just want the SFT for k.j to be considered call
clobbered for this testcase.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24169

[Bug tree-optimization/24169] Address (full struct) escapes even though the called function does not cause it to escape

[dberlin at dberlin dot org]

------- Comment #2 from dberlin at gcc dot gnu dot org  2006-01-03 14:58 -------
Subject: Re:  Address (full struct) escapes
        even though the called function does not cause it to escape

On Sun, 2006-01-01 at 00:41 +0000, pinskia at gcc dot gnu dot org wrote:
> 
> ------- Comment #1 from pinskia at gcc dot gnu dot org  2006-01-01 00:41 -------
> Just a clarification here, I just want the SFT for k.j to be considered call
> clobbered for this testcase.
> 
This is not anywhere near as easy as you think it is.

In fact, we used to only call clobber k.j.  Because our standards
experts tell us that doing pointer arithmetic magic to get back to k.i
is legal, we could only consider this function to clobber *just* k.j if
the pointer doesn't escape from f, *and* f does not do any pointer
arithmetic on it's arguments.

This is usually *not* the case, making this testcase more or less "not
interesting at all".


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24169

Re: [Bug tree-optimization/24169] Address (full struct) escapes even though the called function does not cause it to escape

[Daniel Berlin]

On Sun, 2006-01-01 at 00:41 +0000, pinskia at gcc dot gnu dot org wrote:
> 
> ------- Comment #1 from pinskia at gcc dot gnu dot org  2006-01-01 00:41 -------
> Just a clarification here, I just want the SFT for k.j to be considered call
> clobbered for this testcase.
> 
This is not anywhere near as easy as you think it is.

In fact, we used to only call clobber k.j.  Because our standards
experts tell us that doing pointer arithmetic magic to get back to k.i
is legal, we could only consider this function to clobber *just* k.j if
the pointer doesn't escape from f, *and* f does not do any pointer
arithmetic on it's arguments.

This is usually *not* the case, making this testcase more or less "not
interesting at all".

[Bug tree-optimization/24169] Address (full struct) escapes even though the called function does not cause it to escape

[steven at gcc dot gnu dot org]

------- Comment #3 from steven at gcc dot gnu dot org  2010-07-15 22:50 -------
Would be quite useful, though, for languages that do not have/allow pointer
arithmetic.


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2006-08-21 06:09:02         |2010-07-15 22:50:25
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24169

[Bug tree-optimization/24169] Address (full struct) escapes even though the called function does not cause it to escape

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2010-07-16 08:29 -------
IPA-PTA computes the required information (but we do not store sub-field
granular points-to or clobber sets):

h.clobber = { k.8+8 }
h.use = { }
f.clobber = { k.8+8 } same as f.arg0
f.use = { }
f.arg0 = { k.8+8 }
k.0+8 = { }
k.8+8 = { }

<bb 2>:
  k.i = 2;
  k.j = 2;
  # CLB = { k }
  f (&k.j);
  D.2724_1 = k.i;
  if (D.2724_1 != 2)
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 3>:
  # USE = nonlocal
  # CLB = nonlocal
  link_error ();

<bb 4>:
  return;


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2010-07-15 22:50:25         |2010-07-16 08:29:05
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24169