[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

amker at gcc dot gnu.org changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |FIXED

--- Comment #9 from amker at gcc dot gnu.org ---
Fixed.

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #8 from amker at gcc dot gnu.org ---
vect_perm added for the the test case.  It should be bypassed now on
sparc-sun-solaris2.12?

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #7 from amker at gcc dot gnu.org ---
(In reply to Rainer Orth from comment #6)
> Created attachment 41456 [details]
> sparc-sun-solaris2.12 pr80815-3.c.156t.vect

Thanks for reporting, I will investigate it and disable on targets if it's not
a general case.

Thanks.

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[ro at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

Rainer Orth  changed:

   What|Removed |Added

 CC||ro at gcc dot gnu.org

--- Comment #6 from Rainer Orth  ---
Created attachment 41456
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41456=edit
sparc-sun-solaris2.12 pr80815-3.c.156t.vect

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #5 from amker at gcc dot gnu.org ---
Author: amker
Date: Fri May 26 14:18:26 2017
New Revision: 248512

URL: https://gcc.gnu.org/viewcvs?rev=248512=gcc=rev
Log:
PR tree-optimization/80815
* tree-data-ref.c (prune_runtime_alias_test_list): Simplify condition
for merging runtime alias checks.  Handle negative DR_STEPs.
gcc/testsuite
* gcc.dg/vect/pr80815-1.c: New test.
* gcc.dg/vect/pr80815-2.c: New test.

Added:
trunk/gcc/testsuite/gcc.dg/vect/pr80815-1.c
trunk/gcc/testsuite/gcc.dg/vect/pr80815-2.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/testsuite/ChangeLog
trunk/gcc/tree-data-ref.c

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #4 from amker at gcc dot gnu.org ---
Also the three cases:
  /* If the left segment does not extend beyond the start of the
 right segment the new segment length is that of the right
 plus the segment distance.  */
  if (tree_fits_uhwi_p (dr_a1->seg_len)
  && compare_tree_int (dr_a1->seg_len, diff) <= 0)
{
  dr_a1->seg_len = size_binop (PLUS_EXPR, dr_a2->seg_len,
   size_int (diff));
  do_remove = true;
}
  /* Generally the new segment length is the maximum of the
 left segment size and the right segment size plus the distance.
 ???  We can also build tree MAX_EXPR here but it's not clear this
 is profitable.  */
  else if (tree_fits_uhwi_p (dr_a1->seg_len)
   && tree_fits_uhwi_p (dr_a2->seg_len))
{
  unsigned HOST_WIDE_INT seg_len_a1 = tree_to_uhwi
(dr_a1->seg_len);
  unsigned HOST_WIDE_INT seg_len_a2 = tree_to_uhwi
(dr_a2->seg_len);
  dr_a1->seg_len = size_int (MAX (seg_len_a1, diff + seg_len_a2));
  do_remove = true;
}
  /* Now we check if the following condition is satisfied:

 DIFF - SEGMENT_LENGTH_A < SEGMENT_LENGTH_B

 where DIFF = DR_A2_INIT - DR_A1_INIT.  However,
 SEGMENT_LENGTH_A or SEGMENT_LENGTH_B may not be constant so we
 have to make a best estimation.  We can get the minimum value
 of SEGMENT_LENGTH_B as a constant, represented by MIN_SEG_LEN_B,
 then either of the following two conditions can guarantee the
 one above:

 1: DIFF <= MIN_SEG_LEN_B
 2: DIFF - SEGMENT_LENGTH_A < MIN_SEG_LEN_B  */
  else
{
  unsigned HOST_WIDE_INT min_seg_len_b
= (tree_fits_uhwi_p (dr_b1->seg_len)
   ? tree_to_uhwi (dr_b1->seg_len)
   : factor);

  if (diff <= min_seg_len_b
  || (tree_fits_uhwi_p (dr_a1->seg_len)
  && diff - tree_to_uhwi (dr_a1->seg_len) < min_seg_len_b))
{
  dr_a1->seg_len = size_binop (PLUS_EXPR,
   dr_a2->seg_len, size_int
(diff));
  do_remove = true;
}
}

Can be merged together.  the merged dr_a1->seg_len is dr_a2->seg_len + diff,
with an exception checking MAX (seg_len_a1, diff + seg_len_a2).

Of course, negative step still needs to be handled.

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #3 from amker at gcc dot gnu.org ---
(In reply to rguent...@suse.de from comment #2)
> On Fri, 19 May 2017, amker at gcc dot gnu.org wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815
> > 
> > --- Comment #1 from amker at gcc dot gnu.org ---
> > GCC uses vect_factor as minimal segment length for dr_b when merging alias
> > pairs, I think it could be relaxed to vect_factor * abs (DR_STEP (dr_b)). 
> > Below test shows this change can merge additional alias checks:
> 
> But it would make cases aliasing that are not (that's always a trade off
> between more precise result and less runtime checking).

Hmm, it only does compilation time (and still conservative) check if segment
dr_b resides in the gap between dr_a1 and dr_a2.  the overall effect would be
equal to checking ,  and ?

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #2 from rguenther at suse dot de  ---
On Fri, 19 May 2017, amker at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815
> 
> --- Comment #1 from amker at gcc dot gnu.org ---
> GCC uses vect_factor as minimal segment length for dr_b when merging alias
> pairs, I think it could be relaxed to vect_factor * abs (DR_STEP (dr_b)). 
> Below test shows this change can merge additional alias checks:

But it would make cases aliasing that are not (that's always a trade off
between more precise result and less runtime checking).

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #1 from amker at gcc dot gnu.org ---
GCC uses vect_factor as minimal segment length for dr_b when merging alias
pairs, I think it could be relaxed to vect_factor * abs (DR_STEP (dr_b)). 
Below test shows this change can merge additional alias checks:

#include 

int arr[2048];

int
foo (int *a, int *b, int len)
{
  int i;
  int *a1 = a;
  int *a0 = a1 - 4;
  for (i = 0; i < len; i++)
{
  *b = *a0 + *a1;
  b--;
  a0++;
  a1++;
}
  return 0;
}

int main (void)
{
  int *a = [1027];
  int *b = [1024];

  int i;
  for (i = 0; i < 2048; i++)
arr[i] = i;

  foo (a, b, 500);

  for (i = 0; i < 2048; i++)
fprintf (stdout, "%d: %d\n", i, arr[i]);

  return 0;
}

$ ./gcc -Ofast -fno-inline ./z.c -o z.exe -fdump-tree-vect-details

Of course, alias check should fail and vectorized loop in foo should never be
executed.
Thanks,

[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

amker at gcc dot gnu.org changed:

   What|Removed |Added

   Keywords||wrong-code
   Priority|P3  |P2