[Bug tree-optimization/17046] New: An unused array is not optimized away.

[Bug tree-optimization/17046] New: An unused array is not optimized away.

[kazu at cs dot umass dot edu]

Consider:

static const int banana[] = { 0, 1, 2, 3 };

int
foo (void)
{
  int a = banana[2];
  return a * 0;
}

./cc1 -O2 -fomit-frame-pointer generates:

        .file   "test.c"
        .section        .rodata
        .align 4
        .type   banana, @object
        .size   banana, 16
banana:
        .long   0
        .long   1
        .long   2
        .long   3
        .text
        .p2align 2,,3
.globl foo
        .type   foo, @function
foo:
        xorl    %eax, %eax
        ret
        .size   foo, .-foo
        .ident  "GCC: (GNU) 3.5.0 20040816 (experimental)"
        .section        .note.GNU-stack,"",@progbits

Note that array "banana" is not optimized away.

-- 
           Summary: An unused array is not optimized away.
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17046

[Bug tree-optimization/17046] An unused array is not optimized away.

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-08-16 07:02 -------
Confirmed, I think this is a case where we are marking the static variable as referenced too early.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-08-16 07:02:20
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17046

[Bug tree-optimization/17046] An unused array is not optimized away.

[kazu at cs dot umass dot edu]

------- Additional Comments From kazu at cs dot umass dot edu  2004-08-16 07:31 -------
Yes.  In fact, the following piece of code does *not*
generate the array in the assembly output.

static const int banana[] = { 0, 1, 2, 3 };

int
foo (void)
{
  return banana[2] * 0;
}

Note that the fix for this bug is important so that we can cleanly
fix PR 14841 because uses of "static const arrays" may disappear
during tree optimization.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17046

[Bug tree-optimization/17046] An unused array is not optimized away.

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-04 02:16 -------
Fixed for 4.1.0, most likely by the patches by Jan Honza.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17046