[Bug tree-optimization/36343] New: Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[Bug tree-optimization/36343] New: Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

extern void abort (void);

void __attribute__((noinline))
bar (int **p)
{
  float *q = (float *)p;
  *q = 0.0;
}

float __attribute__((noinline))
foo (int b)
{
  int *i = 0;
  float f = 1.0;
  int **p;
  if (b)
    p = &i;
  else
    p = (int **)&f;
  bar (p);
  if (b)
    return **p;
  return f;
}

int main()
{
  if (foo(0) != 0.0)
    abort ();
  return 0;
}


We TBAA-prune the points-to-set of p due to the dereference *p but use
the pruned points-to-set for computing the call-clobber variables which
causes f not to be call-clobbered.  Thus we return 1.0 from foo.  Oops.


-- 
           Summary: Wrong code due to bad TBAA pruning of points-to-sets and
                    use in call clobbering
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Keywords: wrong-code, alias
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3/4.4 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-05-27 12:45:45
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3/4.4 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2008-05-27 12:45 -------
If you investigate why this doesn't happen more often you find that
directly_dereferenced is only ever set if you dereference a pointer and the
result is also a pointer.  (Thus the complicated testcase)

In essence - we almost _never_ TBAA-prune the points-to-sets.

The correct solution is (apart from improving the TBAA-pruning) to use the
original points-to solution for computing the call-clobbered variables, not
the TBAA-pruned points-to set.

For 4.3 the easiest and least invasive solution is to rip out the
TBAA-pruning code completely.  This is also the temporary solution for the
mainline.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.3.0 4.4.0
      Known to work|                            |4.1.3 4.2.4
            Summary|Wrong code due to bad TBAA  |[4.3/4.4 Regression] Wrong
                   |pruning of points-to-sets   |code due to bad TBAA pruning
                   |and use in call clobbering  |of points-to-sets and use in
                   |                            |call clobbering
   Target Milestone|---                         |4.3.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3/4.4 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3/4.4 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2008-05-29 10:32 -------
Subject: Bug 36343

Author: rguenth
Date: Thu May 29 10:31:58 2008
New Revision: 136152

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=136152
Log:
2008-05-29  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/36343
        PR tree-optimization/36346
        PR tree-optimization/36347
        * tree-flow.h (clobber_what_p_points_to): Declare.
        * tree-ssa-structalias.c (set_uids_in_ptset): Whether the
        pointed-to variable is dereferenced is irrelevant to whether
        the pointer can access the pointed-to variable.
        (clobber_what_p_points_to): New function.
        * tree-ssa-alias.c (set_initial_properties): Use it.
        * tree-ssa.c (verify_flow_sensitive_alias_info): Adjust
        call clobber check for NMTs.

        * gcc.c-torture/execute/pr36343.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr36343.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-flow.h
    trunk/gcc/tree-ssa-alias.c
    trunk/gcc/tree-ssa-structalias.c
    trunk/gcc/tree-ssa.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3/4.4 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-05-29 10:34 -------
Fixed on the mainline.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|4.3.0 4.4.0                 |4.3.0
      Known to work|4.1.3 4.2.4                 |4.1.3 4.2.4 4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2008-06-06 14:59 -------
4.3.1 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.1                       |4.3.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[jsm28 at gcc dot gnu dot org]

------- Comment #5 from jsm28 at gcc dot gnu dot org  2008-08-27 22:04 -------
4.3.2 is released, changing milestones to 4.3.3.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.2                       |4.3.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2008-09-17 14:46 -------
Created an attachment (id=16344)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16344&action=view)
patch disabling TBAA pruning

This is the patch we use for openSUSE to fix this bug.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[ebotcazou at gcc dot gnu dot org]

------- Comment #7 from ebotcazou at gcc dot gnu dot org  2008-09-17 15:07 -------
> This is the patch we use for openSUSE to fix this bug.

Any particular reason for not installing it at the FSF as well?


-- 

ebotcazou at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenther at suse dot de]

------- Comment #8 from rguenther at suse dot de  2008-09-17 15:10 -------
Subject: Re:  [4.3 Regression] Wrong code due
 to bad TBAA pruning of points-to-sets and use in call clobbering

On Wed, 17 Sep 2008, ebotcazou at gcc dot gnu dot org wrote:

> ------- Comment #7 from ebotcazou at gcc dot gnu dot org  2008-09-17 15:07 -------
> > This is the patch we use for openSUSE to fix this bug.
> 
> Any particular reason for not installing it at the FSF as well?

It disables optimizations and the testcase was artificially created by
me from looking at the source.  But let me just submit the patch
(again) and ask for feedback.

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2008-09-19 15:05 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to fail|4.3.0                       |4.3.0 4.3.2
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343

[Bug tree-optimization/36343] [4.3 Regression] Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2008-09-19 15:06 -------
Subject: Bug 36343

Author: rguenth
Date: Fri Sep 19 15:04:36 2008
New Revision: 140492

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=140492
Log:
2008-09-19  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/36343
        * tree-ssa-structalias.c (struct variable_info): Remove
        directly_dereferenced member.
        (new_var_info): Do not set it.
        (process_constraint_1): Likewise.
        (set_uids_in_ptset): Remove TBAA-pruning code.
        (find_what_p_points_to): Do not pass TBAA-pruning related
        parameters.

        * gcc.c-torture/execute/pr36343.c: New testcase.

Added:
    branches/gcc-4_3-branch/gcc/testsuite/gcc.c-torture/execute/pr36343.c
Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_3-branch/gcc/tree-ssa-structalias.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343