[Bug tree-optimization/24694] New: Address taken and addressable variables and call clobber

[Bug tree-optimization/24694] New: Address taken and addressable variables and call clobber

[pinskia at gcc dot gnu dot org]

Take the following code:
int f(int);
int g(void)
{
  int i;
  int *iptr = &i;
  int **ipp = &iptr;
  **ipp = 1;
  f(i);
  return **ipp;
}
----------
Here we consider i being call clobber because we lose the fact that iptr is
addressable but we don't look to see if its address escapes at all (which in
this case it does not).


-- 
           Summary: Address taken and addressable variables and call clobber
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         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=24694

[Bug tree-optimization/24694] Address taken and addressable variables and call clobber

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-11-06 15:47 -------
Found this while looking a little into PR 24689.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24694

[Bug tree-optimization/24694] Address taken and addressable variables and call clobber

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2005-11-06 16:08 -------
Note this is not fixed on the iab.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24694

Re: [Bug tree-optimization/24694] New: Address taken and addressable variables and call clobber

[Daniel Berlin]

On Sun, 2005-11-06 at 15:46 +0000, pinskia at gcc dot gnu dot org wrote:
> Take the following code:
> int f(int);
> int g(void)
> {
>   int i;
>   int *iptr = &i;
>   int **ipp = &iptr;
>   **ipp = 1;
>   f(i);
>   return **ipp;
> }
> ----------
> Here we consider i being call clobber because we lose the fact that iptr is
> addressable 

> but we don't look to see if its address escapes at all (which in
> this case it does not).
No, we don't actually.
In fact, that's not even close to what happens.

iptr isn't renamed, and thus, we assume the address taking of i and storage into iptr is the same as a global store, 
because we know nothing about unrenamed variables.

[Bug tree-optimization/24694] Address taken and addressable variables and call clobber

[dberlin at dberlin dot org]

------- Comment #3 from dberlin at gcc dot gnu dot org  2005-11-06 23:59 -------
Subject: Re:   New: Address taken and
        addressable variables and call clobber

On Sun, 2005-11-06 at 15:46 +0000, pinskia at gcc dot gnu dot org wrote:
> Take the following code:
> int f(int);
> int g(void)
> {
>   int i;
>   int *iptr = &i;
>   int **ipp = &iptr;
>   **ipp = 1;
>   f(i);
>   return **ipp;
> }
> ----------
> Here we consider i being call clobber because we lose the fact that iptr is
> addressable 

> but we don't look to see if its address escapes at all (which in
> this case it does not).
No, we don't actually.
In fact, that's not even close to what happens.

iptr isn't renamed, and thus, we assume the address taking of i and storage
into iptr is the same as a global store, 
because we know nothing about unrenamed variables.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24694

[Bug tree-optimization/24694] Address taken and addressable variables and call clobber

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2005-12-30 18:28 -------
And there is a fixme in the source for this problem:
      /* FIXME: LHS is not an SSA_NAME.  Even if it's an assignment to a
         local variables we cannot be sure if it will escape, because we
         don't have information about objects not in SSA form.  Need to
         implement something along the lines of

         J.-D. Choi, M. Gupta, M. J. Serrano, V. C. Sreedhar, and S. P.
         Midkiff, ``Escape analysis for java,'' in Proceedings of the
         Conference on Object-Oriented Programming Systems, Languages, and
         Applications (OOPSLA), pp. 1-19, 1999.  */

So confirming.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |FIXME
   Last reconfirmed|0000-00-00 00:00:00         |2005-12-30 18:28:19
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24694

[Bug tree-optimization/24694] Address taken and addressable variables and call clobber

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2009-04-22 23:09 -------
This problem is harder than what is mentioned, I am going to close this as
won't fix.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24694