[Bug tree-optimization/25558] New: Arguments cannot alias local variables

[Bug tree-optimization/25558] New: Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

I cannot remember if I filed a bug about this or not but I noticed this while
looking at some Fortran code.  Here is testcase which shows the issue:
void link_error(void);

int *t;
int g(int *a)
{
  t = a;
  *a = 2;
}

void f(int *a)
{
  int b;
  b = 1;
  g(&b);
  b = 2;
  *a = 1;  <--- a cannot point to b here.
  if (b == 2)
    link_error();
}

int main(void)
{
  int t;
  f(&t);
  return 0;
}


-- 
           Summary: Arguments cannot alias local variables
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: missed-optimization, alias
          Severity: normal
          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=25558

[Bug tree-optimization/25558] Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-12-25 04:16 -------
Woops I had messed up the testcase, anyways the following line:
  if (b == 2)
Should be replaced with:
  if (b != 2)


This is already done on the RTL level.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |TREE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558

[Bug tree-optimization/25558] Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2005-12-25 04:19 -------
CSE is the one which does this on the rtl level.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |19721
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558

[Bug tree-optimization/25558] Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558

[Bug tree-optimization/25558] Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-12-25 04:56 -------
What is interesting is that ICC does not even do this optimization.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558

[Bug tree-optimization/25558] Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2005-12-25 05:04 -------
(In reply to comment #3)
> What is interesting is that ICC does not even do this optimization.

Even LLVM does this optimization, I am starting to think ICC is not really a
good compiler.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558

[Bug tree-optimization/25558] Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2005-12-25 05:30 -------
(In reply to comment #4)
> (In reply to comment #3)
> > What is interesting is that ICC does not even do this optimization.
> 
> Even LLVM does this optimization, I am starting to think ICC is not really a
> good compiler.

Ifort actually does this optimization, it is just weird that.  Here is the
equivalent Fortran code:
module f1
contains
function g(a)
integer g
integer a
g = 1
a = 2
end function
function f(a)
real f
integer a
integer b
integer c
b=1
c = g(b)
b = 1
a = 2
if (b .ne. 1) then
call link_error ()
end if
f = 1
end function
end module


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558

[Bug tree-optimization/25558] Arguments cannot alias local variables

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2006-01-11 01:07 -------
Oh, this is a dup of bug 23086.

*** This bug has been marked as a duplicate of 23086 ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558