[Bug tree-optimization/56625] New: After if-conversion vectorizer doesn't recognize similar stores

[Bug tree-optimization/56625] New: After if-conversion vectorizer doesn't recognize similar stores

[michael.v.zolotukhin at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56625

             Bug #: 56625
           Summary: After if-conversion vectorizer doesn't recognize
                    similar stores
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: michael.v.zolotukhin@gmail.com
                CC: kirill.yukhin@intel.com,
                    michael.v.zolotukhin@gmail.com
             Build: 4.8.0 20130313


Created attachment 29673
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29673
Reproducer

In the following example there are two stores a[i]<-b[i] after if-conversion.
void foo (double a[], double b[])
{
  int i;
  for (i = 0; i < 100; i++)
    {
      if (a[i] == 0)
        a[i] = b[i]*4;
      else
        a[i] = b[i]*3;
    }
}
As vectorizer knows nothing about dependencies between a and b, it needs a
runtime test for it. But in the given example, vectorizer generates two
runtime-tests instead of one:
note: mark for run-time aliasing test between *_11 and *_8
note: mark for run-time aliasing test between *_15 and *_8

The test is attached, command line to reproduce:
gcc if-conv-runtime-tests.c -O3 -c -ftree-vectorizer-verbose=15
-ftree-loop-if-convert-stores  -fdump-tree-vect

[Bug tree-optimization/56625] After if-conversion vectorizer doesn't recognize similar stores

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56625

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2013-03-15
     Ever Confirmed|0                           |1
              Build|4.8.0 20130313              |

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-15 12:27:08 UTC ---
For me cselim already sinks the store, making this a non-issue (and vectorizing
the loop).  On x86_64, that is.

So - which target?

[Bug tree-optimization/56625] After if-conversion vectorizer doesn't recognize similar loads

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56625

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
            Summary|After if-conversion         |After if-conversion
                   |vectorizer doesn't          |vectorizer doesn't
                   |recognize similar stores    |recognize similar loads

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-15 12:29:50 UTC ---
Oh, it's about the loads!

  <bb 3>:
  # i_22 = PHI <i_19(4), 0(2)>
  # ivtmp_28 = PHI <ivtmp_24(4), 100(2)>
  _5 = (long unsigned int) i_22;
  _6 = _5 * 8;
  _8 = a_7(D) + _6;
  _9 = *_8;
  _11 = b_10(D) + _6;
  _12 = *_11;
  _13 = _12 * 4.0e+0;
  _15 = b_10(D) + _6;
  _16 = *_15;
  _17 = _16 * 3.0e+0;
  cstore_18 = _9 == 0.0 ? _13 : _17;
  *_8 = cstore_18;

and

t.c:4: note: versioning for alias required: can't determine dependence between
*_11 and *_8
t.c:4: note: mark for run-time aliasing test between *_11 and *_8
t.c:4: note: versioning for alias required: can't determine dependence between
*_15 and *_8
t.c:4: note: mark for run-time aliasing test between *_15 and *_8

Creating dr for *_11
analyze_innermost: success.
        base_address: b_10(D)
        offset from base address: 0
        constant offset from base address: 0
        step: 8
        aligned to: 128
        base_object: *b_10(D)
        Access function 0: {0B, +, 8}_1
Creating dr for *_15
analyze_innermost: success.
        base_address: b_10(D)
        offset from base address: 0
        constant offset from base address: 0
        step: 8
        aligned to: 128
        base_object: *b_10(D)
        Access function 0: {0B, +, 8}_1

somehow the equality test (which we have!) doesn't work here.