[Bug c++/30840] New: ice for legal code with flags -O3 -fno-strict-aliasing

[Bug c++/30840] New: ice for legal code with flags -O3 -fno-strict-aliasing

[dcb314 at hotmail dot com]

I just tried to compile Suse Linux package rxvt-unicode-8.1-3
with the GNU C++ compiler version 4.3 snapshot 20070216.

The compiler said

screen.C: In member function 'void rxvt_term::scr_reset()':
screen.C:160: internal compiler error: in set_lattice_value, at
tree-ssa-ccp.c:487
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.

Preprocessed source code attached. Flags -O3 -fno-strict-aliasing required.


-- 
           Summary: ice for legal code with flags -O3 -fno-strict-aliasing
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dcb314 at hotmail dot com
  GCC host triplet: x86_64-suse-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug c++/30840] ice for legal code with flags -O3 -fno-strict-aliasing

[dcb314 at hotmail dot com]

------- Comment #1 from dcb314 at hotmail dot com  2007-02-18 11:28 -------
Created an attachment (id=13063)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13063&action=view)
C++ source code


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] ice for legal code with flags -O3 -fno-strict-aliasing

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-02-18 22:12 -------
Reducing ...


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |tree-optimization
            Summary|ice for legal code with     |ice for legal code with
                   |flags -O3 -fno-strict-      |flags -O3 -fno-strict-
                   |aliasing                    |aliasing


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2007-02-19 06:53 -------
Confirmed, reduced testcase as far as I can do it:
typedef struct rxvt_term *rxvt_t;
struct rxvt_salloc {
        struct chain {
                struct chain *next;
        };
        chain *firstline;
        unsigned int firstfree;
        inline void alloc ();
};
struct rxvt_perl_interp {
        bool invoke (rxvt_term *term);
};
extern struct rxvt_perl_interp rxvt_perl;
struct rxvt_term   {
        int term_start;
        int *row_buf;
        rxvt_salloc *talloc;
        void scr_reset (int pend, int qlines);
};
inline void rxvt_salloc::alloc ()
{
        if (firstline)
                firstline = firstline->next;
        else    {
                if (firstfree > 65536)
                        firstfree = sizeof (chain);
                firstfree += firstfree;
        }
}
void rxvt_term::scr_reset (int pend, int qlines) {
        do      {
                int *qline;
                for (int qrow = term_start; qlines--; qrow++)
                {
                        qline = row_buf + qrow;
                        talloc->alloc ();
                        talloc->alloc ();
                }
                qline[0]  &= ~0x0001;
                talloc->alloc ();
                talloc->alloc ();
        }       while (term_start != pend);
        rxvt_perl.invoke (this);
}


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   GCC host triplet|x86_64-suse-linux           |
           Keywords|                            |ice-on-valid-code
   Last reconfirmed|0000-00-00 00:00:00         |2007-02-19 06:53:25
               date|                            |
            Summary|ice for legal code with     |[4.3 Regression] ice for
                   |flags -O3 -fno-strict-      |legal code with flags -O3 -
                   |aliasing                    |fno-strict-aliasing
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2007-02-19 11:31 -------
It seems to be a problem with ssa-edge simulation ordering.  We have

# SMT.6_95 = VDEF <SMT.6_60>
# SMT.8_96 = VDEF <SMT.8_70>
this_22->firstfree = D.2527_46;

in particular, adding only the first output to simulate

      /* Note that for propagation purposes, we are only interested in
         visiting statements that load the exact same memory reference
         stored here.  Those statements will have the exact same list
         of virtual uses, so it is enough to set the output of this
         statement to be its first virtual definition.  */
      *output_p = first_vdef (stmt);
      if (changed)
        {
          if (val.lattice_val == VARYING)
            retval = SSA_PROP_VARYING;

will cause a missed propagation of the new lattice value to PHI results.
Another point is that get_value_loaded_by will return NULL for the two
VOPs where one has a CONSTANT and one a VARYING value and so we'll call
evaluate_stmt on the stmt which will return UNDEFINED which causes us to
go back from VARYING to UNDEFINED.  Boom.

Sth. like the following fixes it (note 'VARYING' is unknown to
tree-ssa-propagate.c):

Index: tree-ssa-propagate.c
===================================================================
*** tree-ssa-propagate.c        (revision 122127)
--- tree-ssa-propagate.c        (working copy)
*************** get_value_loaded_by (tree stmt, prop_val
*** 835,850 ****
    tree vuse;
    prop_value_t *prev_val = NULL;
    prop_value_t *val = NULL;

    FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, i, SSA_OP_VIRTUAL_USES)
      {
        val = &values[SSA_NAME_VERSION (vuse)];
        if (prev_val && prev_val->value != val->value)
!       return NULL;
!       prev_val = val;
      }

!   return val;
  }


--- 841,860 ----
    tree vuse;
    prop_value_t *prev_val = NULL;
    prop_value_t *val = NULL;
+   bool valid = true;

+   /* Make sure to set the result to varying if any of the operands is
+      varying.  */
    FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, i, SSA_OP_VIRTUAL_USES)
      {
        val = &values[SSA_NAME_VERSION (vuse)];
        if (prev_val && prev_val->value != val->value)
!       valid = false;
!       if (!prev_val || prev_val->lattice_val < val->lattice_val)
!         prev_val = val;
      }

!   return (valid || prev_val->lattice_val == 3) ? prev_val : NULL;
  }


Index: tree-ssa-ccp.c
===================================================================
*** tree-ssa-ccp.c      (revision 122127)
--- tree-ssa-ccp.c      (working copy)
*************** visit_assignment (tree stmt, tree *outpu
*** 1208,1215 ****
        prop_value_t *nval = get_value_loaded_by (stmt, const_val);

        if (nval
!         && nval->mem_ref
!         && operand_equal_p (nval->mem_ref, rhs, 0))
        val = *nval;
        else
        val = evaluate_stmt (stmt);
--- 1208,1216 ----
        prop_value_t *nval = get_value_loaded_by (stmt, const_val);

        if (nval
!         && ((nval->mem_ref
!              && operand_equal_p (nval->mem_ref, rhs, 0))
!             || nval->lattice_val == VARYING))
        val = *nval;
        else
        val = evaluate_stmt (stmt);


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dnovillo at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2007-02-19 12:56 -------
We can also simply check before the fact like

Index: tree-ssa-ccp.c
===================================================================
*** tree-ssa-ccp.c      (revision 122127)
--- tree-ssa-ccp.c      (working copy)
*************** visit_assignment (tree stmt, tree *outpu
*** 1212,1218 ****
          && operand_equal_p (nval->mem_ref, rhs, 0))
        val = *nval;
        else
!       val = evaluate_stmt (stmt);
      }
    else
      /* Evaluate the statement.  */
--- 1212,1226 ----
          && operand_equal_p (nval->mem_ref, rhs, 0))
        val = *nval;
        else
!       {
!         val = evaluate_stmt (stmt);
!         /* We need to be careful not to drop back to UNDEFINED from
!            VARYING.  This can happen because we only re-process the
!            first virtual operand of a store.  */
!         if (val.lattice_val == UNDEFINED
!             && get_value (lhs)->lattice_val > UNDEFINED)
!           val.lattice_val = VARYING;
!       }
      }
    else
      /* Evaluate the statement.  */

still not simulating the ssa edges for the other virtual operands does not
seem to be the best approach.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[tbm at gcc dot gnu dot org]

------- Comment #6 from tbm at gcc dot gnu dot org  2007-05-19 09:07 -------
*** Bug 31926 has been marked as a duplicate of this bug. ***


-- 

tbm at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jojelino at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2007-06-07 02:47 -------
This testcase works on the trunk on, it was fixed between 20070513 and
20070531.  I will check on the other testcase too.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[reichelt at gcc dot gnu dot org]

------- Comment #8 from reichelt at gcc dot gnu dot org  2007-06-07 21:52 -------
The following simplified testcase still crashes on mainline when compiled
with "-O2":

==============================
struct A
{
  int i, *p;
  A* a;

  void foo()
  {
    if (p)
      p++;
    else
    {
      if (i)
        i = 1;
      i++;
    }
  }

  A();
};

A::A()
{
  int j;
  A* q;

  while (j)
  {
    j--;
    while (j--)
    {
      q = this;
      a->foo();
      a->foo();
    }

    q->a++;
    a->foo();
    a->foo();
  }

  A b;
}
==============================


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[pinskia at gcc dot gnu dot org]

------- Comment #9 from pinskia at gcc dot gnu dot org  2007-08-20 09:18 -------
This testcase needs a rereduction, the two reductions here work now.
Reducing now.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[pinskia at gcc dot gnu dot org]

------- Comment #10 from pinskia at gcc dot gnu dot org  2007-08-20 11:55 -------
Here is a new reduced testcase (compile at -O3 -fno-strict-aliasing):
struct rxvt_salloc {
  char *firstblock;
  unsigned int firstfree;
};
struct line_t {
   unsigned int *t;
   unsigned int f;
};
struct rxvt_salloc *talloc;
struct line_t *row_buf;
static inline unsigned * alloc (struct rxvt_salloc *this1)
{
  void *r;
  if (this1->firstfree > 65536)
    this1->firstfree = 4;
  r = (void *) ((char *)this1->firstblock + this1->firstfree);
  return (unsigned *)r;
}
void
scr_reset (int qlines)
{
  struct line_t *qline;
  int qrow;
  for (qrow = 0; qlines--; qrow++)
      (qline = row_buf)->t = alloc (talloc);
  qline->f &= ~0x0001;
  qline->t = alloc (talloc);
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[pinskia at gcc dot gnu dot org]

------- Comment #11 from pinskia at gcc dot gnu dot org  2007-08-20 11:57 -------
> Here is a new reduced testcase (compile at -O3 -fno-strict-aliasing):
One more note, this testcase ICEs with the C front-end now :).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[pinskia at gcc dot gnu dot org]

------- Comment #12 from pinskia at gcc dot gnu dot org  2007-08-20 12:00 -------
You can also now invoke it just with "-O1 -ftree-store-ccp" :).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[reichelt at gcc dot gnu dot org]

------- Comment #13 from reichelt at gcc dot gnu dot org  2007-08-21 19:50 -------
Here's an even smaller testcase:

=============================
int *p;

inline int foo(int *q)
{
  if (*q)
    *q = 0;
  return *q;
}

void bar(int *r, int i)
{
  int *s;
  while (--i)
    *(s = r) = foo(p);
  ++(*s);
  *s = foo(p);
}
==============================


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[tbm at gcc dot gnu dot org]

------- Comment #14 from tbm at gcc dot gnu dot org  2007-08-25 09:37 -------
*** Bug 32607 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[tbm at gcc dot gnu dot org]

------- Comment #15 from tbm at gcc dot gnu dot org  2007-08-25 09:37 -------
*** Bug 31926 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[janis at gcc dot gnu dot org]

------- Comment #16 from janis at gcc dot gnu dot org  2007-10-19 22:14 -------
A regression hunt on powerpc-linux using the testcase from comment #3
identified this patch:

    http://gcc.gnu.org/viewcvs?view=rev&rev=119502

    r119502 | dberlin | 2006-12-04 19:07:05 +0000 (Mon, 04 Dec 2006)


-- 

janis at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dberlin at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[jakub at gcc dot gnu dot org]

------- Comment #17 from jakub at gcc dot gnu dot org  2007-12-11 12:35 -------
Can't reproduce any ICE on {x86_64,i686,ppc}-linux with here referenced
testcases at various flags (including e.g. -O3 -fno-strict-aliasing
-fno-tree-vectorize to make it more similar to the old setup).
The #c1 testcase went away on x86_64-linux between 200708{20,30}, the #c13
testcase between 200709{07,11}.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[rguenth at gcc dot gnu dot org]

------- Comment #18 from rguenth at gcc dot gnu dot org  2007-12-11 13:20 -------
The dups also all work.  Let's close this as fixed then.


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840

[Bug tree-optimization/30840] [4.3 Regression] ice for legal code with flags -O3 -fno-strict-aliasing

[jakub at gcc dot gnu dot org]

------- Comment #19 from jakub at gcc dot gnu dot org  2007-12-11 13:41 -------
The testcase that was broken longest is #c3, which got fixed by
http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=130222


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30840