[Bug c/52298] New: ICE: verify_ssa failed: definition in block follows use

[Bug c/52298] New: ICE: verify_ssa failed: definition in block follows use

[regehr at cs dot utah.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

             Bug #: 52298
           Summary: ICE: verify_ssa failed: definition in block follows
                    use
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: regehr@cs.utah.edu
                CC: chenyang@cs.utah.edu
              Host: x86_64-unknown-linux-gnu
            Target: x86_64-unknown-linux-gnu
             Build: x86_64-unknown-linux-gnu


regehr@gamow 4]$ current-gcc -O3 -c small.c
small.c: In function 'fn1':
small.c:6:1: error: definition in block 4 follows the use
for SSA_NAME: vect_cst_.18_24 in statement:
vect_var_.19_37 = VEC_PERM_EXPR <vect_cst_.18_24, vect_cst_.18_24, { 3, 2, 1, 0
}>;
small.c:6:1: internal compiler error: verify_ssa failed
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
[regehr@gamow 4]$ cat small.c
int a, b, c, h;

int i[5][5];

void
fn1 ()
{
  int l = 0;

  for (a = 0; a <= 3; a++)
    for (b = 1; b >= 0; b -= 1)
      l |= i[0][b];
  c = l;
}
[regehr@gamow 4]$ current-gcc -v
Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/uusoc/exports/scratch/regehr/z/compiler-install/gcc-r184342-install/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.7.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/compiler-install/gcc-r184342-install
--program-prefix=r184342- --enable-languages=c,c++
Thread model: posix
gcc version 4.7.0 20120217 (experimental) (GCC)

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-02-18
          Component|c                           |tree-optimization
                 CC|                            |jakub at gcc dot gnu.org
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1
   Target Milestone|---                         |4.7.0

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-02-18 10:05:50 UTC ---
Confirmed, looking into it.

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|jakub at gcc dot gnu.org    |unassigned at gcc dot
                   |                            |gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-02-20 08:57:40 UTC ---
Unassigning myself, not familiar enough with the nested_in_vect_loop stuff,
Richard, could you please have a look at this?
Just random comments:

Shorter testcase (-O3):
int a, b, i[2];

int
foo (void)
{
  int l = 0;

  for (a = 0; a <= 3; a++)
    for (b = 1; b >= 0; b--)
      l |= i[b];
  return l;
}

The immediate problem I see is that in vectorizable_load we initialize
  negative = tree_int_cst_compare (DR_STEP (dr), size_zero_node) < 0;
i.e. from the inner loop's step (which is really negative), while we actually
use STMT_VINFO_DR_STEP when deciding if it is invariant and how to adjust the
read in each loop.  STMT_VINFO_DR_STEP is 0 here, i.e. invariant, and
vectorizable_load in that case inserts stmts after the original stmt, but as
negative is true, we then put a permutation of it (which doesn't make any sense
for invariant loads, as all the vector elements are the same) before the
original stmt.  So, a quick hack of ignoring negative if inv_p && !bb_vinfo
fixes this, but can't be the right fix.  I guess negative flag should be taken
from STMT_VINFO_DR_STEP if nested_in_vect_loop, but not sure if always, and the
question is what to do with the testing for the negative case, which needs to
pass a dr around, and for the outer loop we don't have any dr with the right
step etc.

I think the testcase shows several other issues, which can be observed also on
(-O3):

int a, b, i[2];

int
foo (void)
{
  int l = 0;

  for (a = 0; a <= 3; a++)
    for (b = 0; b <= 1; b++)
      l |= i[b];
  return l;
}

1) it is unfortunately cunrolli pass doesn't do anything here, then the
vectorizer wouldn't make such weird decisions; but when cunrolli is run, lim
hasn't moved out the b variable loads/stores from the loop yet, and the next
complete unrolling happens only after vectorization.  Perhaps another inner
loop complete unrolling a couple of passes before vectorization would help
here, but the question is if it would help even real-world apps.

2) if the outer loop has zero step and inner non-zero step, the question is if
it is worthwhile to do the vectorization at all, and at least on the above
testcase the cost model should say that it can't be beneficial given the large
cost of the reduction for a single iteration.

3) after complete unrolling, we end up with:
vect_var_.18_27 = vect_cst_.17_14 | { 0, 0, 0, 0 };
but nothing at the tree level optimizes that away into just
vect_var_.18_27 = vect_cst_.17_14;

So, the resulting assembly:
        movd    i(%rip), %xmm0
        movl    $2, b(%rip)
        movd    i+4(%rip), %xmm2
        movl    $4, a(%rip)
        pshufd  $0, %xmm0, %xmm1
        pshufd  $0, %xmm2, %xmm0
        por     %xmm1, %xmm0
        movdqa  %xmm0, %xmm1
        psrldq  $8, %xmm1
        por     %xmm1, %xmm0
        movdqa  %xmm0, %xmm1
        psrldq  $4, %xmm1
        por     %xmm1, %xmm0
        movd    %xmm0, -12(%rsp)
        movl    -12(%rsp), %eax
        ret
really can't be faster than
        movl    i+4(%rip), %edx
        movl    i(%rip), %eax
        movl    $2, b(%rip)
        movl    $4, a(%rip)
        orl     %edx, %eax
        orl     %edx, %eax
        ret
(but even for the non-vectorized loop, we should optimize away the second orl).

While playing with this, I ended up with a wrong-code testcase as opposed to
ice-on-valid:

/* { dg-options "-O1 -ftree-vectorize -fno-tree-pre -fno-tree-loop-im" } */

extern void abort (void);
int c[80];

__attribute__((noinline)) int
foo (void)
{
  int l = 0;
  int a, b;

  for (a = 3; a >= 0; a--)
    for (b = 7; b >= 0; b--)
      l |= c[a+60];
  return l;
}

int
main ()
{
  int i;
  for (i = 0; i < 60; i++)
    c[i] = 1;
  for (; i < 64; i++)
    c[i] = 1 << (i - 59);
  if (foo () != 30)
    abort ();
  return 0;
}

And last minor thing (shouldn't we have a warning for it, at least static code
analyzers should and usually do warn about it):

vect_analyze_data_ref_access does:
  tree step = DR_STEP (dr);
...
  HOST_WIDE_INT dr_step = TREE_INT_CST_LOW (step);
...
  if (loop_vinfo && !step)
    {
      if (vect_print_dump_info (REPORT_DETAILS))
        fprintf (vect_dump, "bad data-ref access in loop");
      return false;
    }
So, either the if should go, because we'd segfault if step is NULL, or
initialization of dr_step needs to be moved after this test.

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-20 12:14:17 UTC ---
Mine.

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-20 13:41:59 UTC ---
DOM optimizes the |s with zero if you adjust the integer_..._p predicates like

Index: gcc/tree.c
===================================================================
--- gcc/tree.c  (revision 184390)
+++ gcc/tree.c  (working copy)
@@ -1714,12 +1714,25 @@ integer_zerop (const_tree expr)
 {
   STRIP_NOPS (expr);

-  return ((TREE_CODE (expr) == INTEGER_CST
-          && TREE_INT_CST_LOW (expr) == 0
-          && TREE_INT_CST_HIGH (expr) == 0)
-         || (TREE_CODE (expr) == COMPLEX_CST
-             && integer_zerop (TREE_REALPART (expr))
-             && integer_zerop (TREE_IMAGPART (expr))));
+  switch (TREE_CODE (expr))
+    {
+    case INTEGER_CST:
+      return (TREE_INT_CST_LOW (expr) == 0
+             && TREE_INT_CST_HIGH (expr) == 0);
+    case COMPLEX_CST:
+      return (integer_zerop (TREE_REALPART (expr))
+             && integer_zerop (TREE_IMAGPART (expr)));
+    case VECTOR_CST:
+      {
+       tree elt;
+       for (elt = TREE_VECTOR_CST_ELTS (expr); elt; elt = TREE_CHAIN (elt))
+         if (!integer_zerop (TREE_VALUE (elt)))
+           return false;
+       return true;
+      }
+    default:
+      return false;
+    }
 }

 /* Return 1 if EXPR is the integer constant one or the corresponding
@@ -1730,12 +1743,25 @@ integer_onep (const_tree expr)
 {
   STRIP_NOPS (expr);

-  return ((TREE_CODE (expr) == INTEGER_CST
-          && TREE_INT_CST_LOW (expr) == 1
-          && TREE_INT_CST_HIGH (expr) == 0)
-         || (TREE_CODE (expr) == COMPLEX_CST
-             && integer_onep (TREE_REALPART (expr))
-             && integer_zerop (TREE_IMAGPART (expr))));
+  switch (TREE_CODE (expr))
+    {
+    case INTEGER_CST:
+      return (TREE_INT_CST_LOW (expr) == 1
+             && TREE_INT_CST_HIGH (expr) == 0);
+    case COMPLEX_CST:
+      return (integer_onep (TREE_REALPART (expr))
+             && integer_zerop (TREE_IMAGPART (expr)));
+    case VECTOR_CST:
+      {
+       tree elt;
+       for (elt = TREE_VECTOR_CST_ELTS (expr); elt; elt = TREE_CHAIN (elt))
+         if (!integer_onep (TREE_VALUE (elt)))
+           return false;
+       return true;
+      }
+    default:
+      return false;
+    }
 }

 /* Return 1 if EXPR is an integer containing all 1's in as much precision as
@@ -1754,6 +1780,15 @@ integer_all_onesp (const_tree expr)
       && integer_zerop (TREE_IMAGPART (expr)))
     return 1;

+  else if (TREE_CODE (expr) == VECTOR_CST)
+    {
+      tree elt;
+      for (elt = TREE_VECTOR_CST_ELTS (expr); elt; elt = TREE_CHAIN (elt))
+       if (!integer_all_onesp (TREE_VALUE (elt)))
+         return 0;
+      return 1;
+    }
+
   else if (TREE_CODE (expr) != INTEGER_CST)
     return 0;


I'll queue that for 4.8.

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-20 14:14:48 UTC ---
Not sure why in vect_model_reduction_cost we do not consider the reduction
at all if nested_in_vect_loop_p (loop, orig_stmt).  I think simply dropping
that conditional would model the cost more appropriately (though the question
is how outer loop vectorization uses the costs).

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

--- Comment #6 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-20 15:16:00 UTC ---
Author: rguenth
Date: Mon Feb 20 15:15:52 2012
New Revision: 184396

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=184396
Log:
2012-02-20  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/52298
    * tree-vect-stmts.c (vectorizable_store): Properly use
    STMT_VINFO_DR_STEP instead of DR_STEP when vectorizing
    outer loops.
    (vectorizable_load): Likewise.
    * tree-vect-data-refs.c (vect_analyze_data_ref_access):
    Access DR_STEP after ensuring it is not NULL.

    * gcc.dg/torture/pr52298.c: New testcase.
    * gcc.dg/vect/pr52298.c: Likewise.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr52298.c
    trunk/gcc/testsuite/gcc.dg/vect/pr52298.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vect-data-refs.c
    trunk/gcc/tree-vect-stmts.c

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-20 15:16:25 UTC ---
Fixed.

[Bug tree-optimization/52298] ICE: verify_ssa failed: definition in block follows use

[uweigand at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52298

--- Comment #8 from Ulrich Weigand <uweigand at gcc dot gnu.org> 2012-02-28 23:40:37 UTC ---
Author: uweigand
Date: Tue Feb 28 23:40:32 2012
New Revision: 184645

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=184645
Log:
    Partially revert:

    2012-02-20  Richard Guenther  <rguenther@suse.de>
    PR tree-optimization/52298
    * tree-vect-stmts.c (vectorizable_load): Properly use
    STMT_VINFO_DR_STEP instead of DR_STEP when vectorizing
    outer loops.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-vect-stmts.c