[Bug tree-optimization/56448] New: cc1 hangs on volatile array with -O or above

[Bug tree-optimization/56448] New: cc1 hangs on volatile array with -O or above

[dhazeghi at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56448

             Bug #: 56448
           Summary: cc1 hangs on volatile array with -O or above
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: dhazeghi@yahoo.com


The following snippet (reduced from a larger test case) causes top-of-trunk cc1
to hang (infinite loop) on x86_64-linux using -O or above.  This is a
regression from 4.7.2 which does not have this issue.

$ cat volatile.c
volatile int a[1];
int b;
void fn1 ()
{
    for (;;)
    {
        int *c[3][6] =
        { 0, 0, 0, &b, 0, 0, 0, 0, &b, 0, 0, 0, 0, 0, 0, 0, &b, (int *)&a[0] };
        b = *c[2][5];
    }
}
$ gcc-trunk --version
gcc-trunk (GCC) 4.8.0 20130225 (experimental) [trunk revision 196255]
$ gcc-4.7 -O -c volatile.c
$ gcc-trunk -c volatile.c
$ gcc-trunk -O -c volatile.c
<hangs>

[Bug tree-optimization/56448] [4.8 Regression] cc1 hangs on volatile array with -O or above

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56448

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-02-25
                 CC|                            |jakub at gcc dot gnu.org
   Target Milestone|---                         |4.8.0
            Summary|cc1 hangs on volatile array |[4.8 Regression] cc1 hangs
                   |with -O or above            |on volatile array with -O
                   |                            |or above
     Ever Confirmed|0                           |1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-25 22:17:01 UTC ---
Started with my http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195136 fix.
I think the problem is that for:
tree val; // which is &a[0] where a is volatile array
operand_equal_p (val, unshare_expr (val), OEP_PURE_SAME)
is false.

[Bug tree-optimization/56448] [4.8 Regression] cc1 hangs on volatile array with -O or above

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56448

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-25 22:40:42 UTC ---
Created attachment 29536
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29536
gcc48-pr56448.patch

Untested fix.
For OEP_CONSTANT_ADDRESS_OF, we should ignore side-effects of the reference
from which the address is taken, they change the value, not its address.
OEP_CONSTANT_ADDRESS_OF in flags is fine to propagate to the first operand of
some references, so e.g. &a.b[0].c[9] is constant, even when c and b arrays are
volatile, but not the other arguments (e.g. array indexes, etc.), but for
*MEM_REF not even the first argument should get that.

[Bug tree-optimization/56448] [4.8 Regression] cc1 hangs on volatile array with -O or above

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56448

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-26 10:00:55 UTC ---
Author: jakub
Date: Tue Feb 26 10:00:31 2013
New Revision: 196278

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196278
Log:
    PR tree-optimization/56448
    * fold-const.c (operand_equal_p) <case tcc_reference>: Don't look at
    TREE_SIDE_EFFECTS if flags contain OEP_CONSTANT_ADDRESS_OF.
    Clear OEP_CONSTANT_ADDRESS_OF from flags before recursing on second or
    later operands of the references, or even first operand for
    INDIRECT_REF, TARGET_MEM_REF or MEM_REF.

    * gcc.c-torture/compile/pr56448.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/compile/pr56448.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/fold-const.c
    trunk/gcc/testsuite/ChangeLog

[Bug tree-optimization/56448] [4.8 Regression] cc1 hangs on volatile array with -O or above

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56448

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-26 10:19:31 UTC ---
Fixed.

[Bug tree-optimization/56448] [4.8 Regression] cc1 hangs on volatile array with -O or above

[dhazeghi at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56448

--- Comment #5 from Dara Hazeghi <dhazeghi at yahoo dot com> 2013-02-26 17:47:04 UTC ---
Thanks!  That was a very quick fix.