[Bug tree-optimization/22615] New: [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[Bug tree-optimization/22615] New: [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[pinskia at gcc dot gnu dot org]

Take the following C++ code, with -O1 we ICE right now (This is forwarded from PR 22277 because the 
orginal bug there was fixed):

struct A
{
  char c;
  int i;
};

A a;

struct B
{
  char c, d;
};

union C
{
  A *p;
  B *q;

  C() : p(&a) {}
  char& foo() { return q->d; }
};

void bar() { C().foo() = 0; }

-- 
           Summary: [4.1 Regression] ICE in first_vi_for_offset, at tree-
                    ssa-structalias.c:2858
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: dberlin at gcc dot gnu dot org,gcc-bugs at gcc dot gnu
                    dot org
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615

[Bug tree-optimization/22615] [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-07-22 18:53 -------
Confirmed, because this is forwarding from one bug to another.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-07-22 18:53:56
               date|                            |
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615

[Bug tree-optimization/22615] [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-11 02:15 -------
first_vi_for_offset

Just to get a search off the comments to find this.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615

[Bug tree-optimization/22615] [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[rguenth at gcc dot gnu dot org]

------- Additional Comments From rguenth at gcc dot gnu dot org  2005-08-11 10:44 -------
We inline all and get

void bar() ()
{
  char & D.1777;
  struct B * D.1776;
  char & D.1773;
  union C D.1772;

<bb 0>:
  D.1772.p = &a;
  D.1776_5 = D.1772.q;
  D.1777_6 = &D.1776_5->d;
  D.1773_7 = D.1777_6;
  *D.1773_7 = 0;
  return;

}

where we access the padding between c and i in struct A through an
object of type B.  This must be invalid code.  Even if it is, the
gcc_unreachable () is probably not a good idea - Danny, how should
we deal with this?  Ignore references to padding and just return
NULL from first_vi_for_offset?

There's a similar problem in get_constraint_for_component_ref which
I hit with array-aliasing and work-around by

*************** get_constraint_for_component_ref (tree t
*** 2075,2082 ****
            }
          /* assert that we found *some* field there. The user couldn't be
             accessing *only* padding.  */
!
!         gcc_assert (curr);
        }
        else
        if (dump_file && (dump_flags & TDF_DETAILS))
--- 2076,2084 ----
            }
          /* assert that we found *some* field there. The user couldn't be
             accessing *only* padding.  */
!         /* Still the user could access one past the end of an array
!            embedded in a struct resulting in accessing *only* padding.  */
!         /* gcc_assert (curr); */
        }
        else
        if (dump_file && (dump_flags & TDF_DETAILS))


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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615

[Bug tree-optimization/22615] [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[rguenth at gcc dot gnu dot org]

------- Additional Comments From rguenth at gcc dot gnu dot org  2005-08-11 10:53 -------
With the patch we make

_Z3barv:
.LFB6:
        pushl   %ebp
.LCFI0:
        movl    %esp, %ebp
.LCFI1:
        movb    $0, a+1
        popl    %ebp
        ret

out of it btw, which looks ok.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615

[Bug tree-optimization/22615] [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[dberlin at dberlin dot org]

------- Additional Comments From dberlin at gcc dot gnu dot org  2005-08-11 12:55 -------
Subject: Re:  [4.1 Regression] ICE in
	first_vi_for_offset, at tree-ssa-structalias.c:2858

On Thu, 2005-08-11 at 10:44 +0000, rguenth at gcc dot gnu dot org wrote:
> ------- Additional Comments From rguenth at gcc dot gnu dot org  2005-08-11 10:44 -------
> We inline all and get
> 
> void bar() ()
> {
>   char & D.1777;
>   struct B * D.1776;
>   char & D.1773;
>   union C D.1772;
> 
> <bb 0>:
>   D.1772.p = &a;
>   D.1776_5 = D.1772.q;
>   D.1777_6 = &D.1776_5->d;
>   D.1773_7 = D.1777_6;
>   *D.1773_7 = 0;
>   return;
> 
> }
> 
> where we access the padding between c and i in struct A through an
> object of type B.  This must be invalid code.  Even if it is, the
> gcc_unreachable () is probably not a good idea - Danny, how should
> we deal with this?  Ignore references to padding and just return
> NULL from first_vi_for_offset?

I know what to do here. I've just been waiting as long as possible to
remove the assert because it also catches real bugs.
I actually plan on removing it today, and have bootstrapped and tested a
patch to do so.

> 
> There's a similar problem in get_constraint_for_component_ref which
> I hit with array-aliasing and work-around by

> 
> *************** get_constraint_for_component_ref (tree t
> *** 2075,2082 ****
>             }
>           /* assert that we found *some* field there. The user couldn't be
>              accessing *only* padding.  */
> !
> !         gcc_assert (curr);
>         }
>         else
>         if (dump_file && (dump_flags & TDF_DETAILS))
> --- 2076,2084 ----
>             }
>           /* assert that we found *some* field there. The user couldn't be
>              accessing *only* padding.  */
> !         /* Still the user could access one past the end of an array
> !            embedded in a struct resulting in accessing *only* padding.  */
> !         /* gcc_assert (curr); */

You are right, but this can only occur with your patch, since it
wouldn't have had fields before, and thus it would have overlapped with
the actual variable, giving the right answer.  :)







-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615

[Bug tree-optimization/22615] [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-08-14 19:24 -------
Subject: Bug 22615

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	dberlin@gcc.gnu.org	2005-08-14 19:23:57

Modified files:
	gcc            : ChangeLog tree-ssa-structalias.c 
Added files:
	gcc/testsuite/g++.dg/tree-ssa: pr22615.C 

Log message:
	2005-08-14  Daniel Berlin  <dberlin@dberlin.org>
	
	Fix PR tree-optimization/22615
	
	* tree-ssa-structalias.c (solution_set_add): Handle
	first_vi_for_offset returning NULL.
	(do_da_constraint): Ditto.
	(do_sd_constraint): Ditto.
	(do_ds_constraint): Ditto
	(find_func_aliases): Ditto.
	(build_constraint_graph): RHS is allowed be ANYTHING.
	(first_vi_for_offset): Return NULL if we couldn't find anything at
	the offset.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.9728&r2=2.9729
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/tree-ssa-structalias.c.diff?cvsroot=gcc&r1=2.26&r2=2.27
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/tree-ssa/pr22615.C.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615

[Bug tree-optimization/22615] [4.1 Regression] ICE in first_vi_for_offset, at tree-ssa-structalias.c:2858

[dberlin at gcc dot gnu dot org]

------- Additional Comments From dberlin at gcc dot gnu dot org  2005-08-14 20:58 -------
Fixed

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22615