[Bug tree-optimization/36493] New: [4.3/4.4 Regression] vectorizer aliasing bug

[Bug tree-optimization/36493] New: [4.3/4.4 Regression] vectorizer aliasing bug

[jsm28 at gcc dot gnu dot org]

The following code aborts if built for i686-pc-linux-gnu with -msse2 -O3.

extern void abort (void);
int
main (void)
{
  int i;
  long x[12] __attribute__((aligned(16)));
  x[0] = 1;
  for (i = 0; i < 12; i++)
    x[i] = i;
  if (x[0] != 0)
    abort ();
  return 0;
}

The loop gets vectorized using "vector int *" pointers, and then the compiler
decides that "vector int" writes don't conflict with "long" reads.  (If an
array of int is used instead, the test passes.)

(Not x86-specific; originally observed as a failure of
gcc.c-torture/execute/loop-13.c on SPE with an unsubmitted patch to support
autovectorization there.)


-- 
           Summary: [4.3/4.4 Regression] vectorizer aliasing bug
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jsm28 at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[irar at il dot ibm dot com]

------- Comment #1 from irar at il dot ibm dot com  2008-06-11 08:00 -------
Reproduced on powerpc64-suse-linux.

Doesn't occur when compiled with -O2 -ftree-vectorize instead of -O3 (the
vectorizer generates the same code in both cases).


-- 

irar at il dot ibm dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-06-11 08:00:41
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2008-06-11 08:37 -------
Vectors have the alias set of their element type and int and long do not have
conflicting alias sets.  The vectorizer clearly should choose vector long *
instead of vector int *.


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[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=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[irar at gcc dot gnu dot org]

------- Comment #3 from irar at gcc dot gnu dot org  2008-06-16 10:39 -------
Subject: Bug 36493

Author: irar
Date: Mon Jun 16 10:39:07 2008
New Revision: 136843

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=136843
Log:
        PR tree-optimization/36493
        * tree-vect-transform.c (vect_create_data_ref_ptr): Remove TYPE from
        the arguments list. Use VECTYPE to create vector pointer.
        (vectorizable_store): Fail if accesses through a pointer to vectype
        do not alias the original memory reference operands.
        Call vect_create_data_ref_ptr without the removed argument.
        (vectorizable_load): Likewise.
        (vect_setup_realignment): Call vect_create_data_ref_ptr without the
        removed argument.


Added:
    trunk/gcc/testsuite/gcc.dg/vect/pr36493.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vect-transform.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[irar at gcc dot gnu dot org]

------- Comment #4 from irar at gcc dot gnu dot org  2008-06-16 10:43 -------
Subject: Bug 36493

Author: irar
Date: Mon Jun 16 10:42:56 2008
New Revision: 136844

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=136844
Log:
        PR tree-optimization/36493
        * tree-vect-transform.c (vect_create_data_ref_ptr): Remove TYPE from
        the arguments list. Use VECTYPE to create vector pointer.
        (vectorizable_store): Fail if accesses through a pointer to vectype
        do not alias the original memory reference operands.
        Call vect_create_data_ref_ptr without the removed argument.
        (vectorizable_load): Likewise.
        (vect_setup_realignment): Call vect_create_data_ref_ptr without the
        removed argument.


Added:
    branches/gcc-4_3-branch/gcc/testsuite/gcc.dg/vect/pr36493.c
Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_3-branch/gcc/tree-vect-transform.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[irar at il dot ibm dot com]

------- Comment #5 from irar at il dot ibm dot com  2008-06-17 11:49 -------
Fixed.


-- 

irar at il dot ibm dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
           Priority|P1                          |P3
         Resolution|                            |FIXED
   Target Milestone|4.3.2                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493

[Bug tree-optimization/36493] [4.3/4.4 Regression] vectorizer aliasing bug

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
   Target Milestone|---                         |4.3.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493