[Bug tree-optimization/60505] New: Warning caused by GCC vectorizer.

[Bug tree-optimization/60505] New: Warning caused by GCC vectorizer.

[congh at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

            Bug ID: 60505
           Summary: Warning caused by GCC vectorizer.
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: congh at google dot com

The compilation on the code below fails with options "-Wall  -Werror -O2
-ftree-loop-vectorize". The reason is that the epilogue generated by the
vectorizer tries to access the memory outside of ovec[16] and the the vrp pass
emits the warning "array subscript is above array bounds" for the access to
ovec[i]. The vectorizer should not generate the epilogue for this loop.



void foo(char *in, char *out, int num)
{
 int i;
 unsigned char ovec[16] = {0};

 for(i=0; i < num ; ++i)
   out[i] = (ovec[i] = in[i]);
 out[num] = ovec[num/2];
}

[Bug tree-optimization/60505] Warning caused by GCC vectorizer.

[congh at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

--- Comment #1 from Cong Hou <congh at google dot com> ---
Google ref: b/13403465

[Bug tree-optimization/60505] Warning caused by GCC vectorizer.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-03-12
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed for the warning.  Note that  'out[num] = ovec[num/2];' at the
end means that num < 16(!) and thus the vectorized loop is never entered
(which means we likely warn for in practice dead code).

[Bug tree-optimization/60505] Warning caused by GCC vectorizer.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Why would out[num] = ovec[num/2]; imply num < 16?  The loop implies num <= 16,
and out[num] = ovec[num/2]; just implies num >= 0 && num <= 31.

[Bug tree-optimization/60505] [4.8/4.9 Regression] Warning caused by GCC vectorizer.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic,
                   |                            |missed-optimization
      Known to work|                            |4.7.3
   Target Milestone|---                         |4.8.3
            Summary|Warning caused by GCC       |[4.8/4.9 Regression]
                   |vectorizer.                 |Warning caused by GCC
                   |                            |vectorizer.

[Bug tree-optimization/60505] [4.8/4.9 Regression] Warning caused by GCC vectorizer.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

Richard Biener <rguenth at gcc dot gnu.org> changed:

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

[Bug tree-optimization/60505] [4.8/4.9 Regression] Warning caused by GCC vectorizer.

[congh at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

--- Comment #4 from Cong Hou <congh at gcc dot gnu.org> ---
Author: congh
Date: Thu Apr  3 23:05:42 2014
New Revision: 209065

URL: http://gcc.gnu.org/viewcvs?rev=209065&root=gcc&view=rev
Log:
2014-04-03  Cong Hou  <congh@google.com>

PR tree-optimization/60505
    * tree-vectorizer.h (struct _stmt_vec_info): Add th field as the
    threshold of number of iterations below which no vectorization will be
    done.
    * tree-vect-loop.c (new_loop_vec_info):
    Initialize LOOP_VINFO_COST_MODEL_THRESHOLD.
    * tree-vect-loop.c (vect_analyze_loop_operations):
    Set LOOP_VINFO_COST_MODEL_THRESHOLD.
    * tree-vect-loop.c (vect_transform_loop):
    Use LOOP_VINFO_COST_MODEL_THRESHOLD.
    * tree-vect-loop.c (vect_analyze_loop_2): Check the maximum number
    of iterations of the loop and see if we should build the epilogue.

2014-04-03  Cong Hou  <congh@google.com>

    PR tree-optimization/60505
    * gcc.dg/vect/pr60505.c: New test.


Added:
    trunk/gcc/testsuite/gcc.dg/vect/pr60505.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vect-loop.c
    trunk/gcc/tree-vectorizer.h

[Bug tree-optimization/60505] [4.8 Regression] Warning caused by GCC vectorizer.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.9.0
            Summary|[4.8/4.9 Regression]        |[4.8 Regression] Warning
                   |Warning caused by GCC       |caused by GCC vectorizer.
                   |vectorizer.                 |
      Known to fail|                            |4.8.2

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk.

[Bug tree-optimization/60505] [4.8 Regression] Warning caused by GCC vectorizer.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.3                       |4.8.4

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 4.8.3 is being released, adjusting target milestone.

[Bug tree-optimization/60505] [4.8 Regression] Warning caused by GCC vectorizer.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.4                       |4.8.5

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.4 has been released.

[Bug tree-optimization/60505] [4.8 Regression] Warning caused by GCC vectorizer.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|4.8.5                       |4.9.0
      Known to fail|                            |4.8.5

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed for 4.9.0.