[Bug tree-optimization/60012] New: Vectorizer generates unnecessary loop versioning for alias

[Bug tree-optimization/60012] New: Vectorizer generates unnecessary loop versioning for alias

[bmei at broadcom dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60012

            Bug ID: 60012
           Summary: Vectorizer generates unnecessary loop versioning for
                    alias
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bmei at broadcom dot com

typedef struct
{
   short real;
   short imag;
} complex16_t;

void
libvector_AccSquareNorm_ref (unsigned long long  *acc,
                             const complex16_t *x, unsigned len)
{
    for (unsigned i = 0; i < len; i++)
    {
        acc[i] +=
            ((unsigned long long)((int)x[i].real * x[i].real)) +
            ((unsigned long long)((int)x[i].imag * x[i].imag));
    }
}

Compiler the code with 
~/scratch/install-x86/bin/gcc tst.c -O2 -S -ftree-vectorize
-fdump-tree-vect-details -std=c99

GCC generates unnecessary loop versioning because it cannot disambiguate mem
accesses. 

tst.c:12:5: note: versioning for alias required: can't determine dependence
between *_8 and _12->real
tst.c:12:5: note: mark for run-time aliasing test between *_8 and _12->real

This should be handled by TBAA info as acc & x clearly point to different data
types. But unfortunately, TBAA doesn't handle Anti- & Output- dependencies.

[Bug tree-optimization/60012] Vectorizer generates unnecessary loop versioning for alias

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60012

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-02-03
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Mine.

[Bug tree-optimization/60012] Vectorizer generates unnecessary loop versioning for alias

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60012

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |4.9.0
         Resolution|---                         |FIXED

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed for 4.9.

[Bug tree-optimization/60012] Vectorizer generates unnecessary loop versioning for alias

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60012

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Tue Feb  4 09:34:58 2014
New Revision: 207455

URL: http://gcc.gnu.org/viewcvs?rev=207455&root=gcc&view=rev
Log:
2014-02-04  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/60012
    * tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Apply
    TBAA disambiguation to all DDRs.

    * gcc.dg/vect/pr60012.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/vect/pr60012.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vect-data-refs.c