[Bug tree-optimization/103029] New: [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[Bug tree-optimization/103029] New: [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[seurer at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

            Bug ID: 103029
           Summary: [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: seurer at gcc dot gnu.org
  Target Milestone: ---

g:f35af8df241a9eb9c2edf7da26d3c5f53d6e2511, r12-4818

This occurs on power 7 (powerpc64 big endian):

make  -k check-gcc RUNTESTFLAGS="vect.exp=gcc.dg/vect/pr82436.c"
FAIL: gcc.dg/vect/pr82436.c (internal compiler error)
FAIL: gcc.dg/vect/pr82436.c (test for excess errors)
FAIL: gcc.dg/vect/pr82436.c -flto -ffat-lto-objects (internal compiler error)
FAIL: gcc.dg/vect/pr82436.c -flto -ffat-lto-objects (test for excess errors)
# of unexpected failures        4


Executing on host: /home/seurer/gcc/git/build/gcc-test/gcc/xgcc
-B/home/seurer/gcc/git/build/gcc-test/gcc/
/home/seurer/gcc/git/gcc-test/gcc/testsuite/gcc.dg/vect/pr82436.c   
-fdiagnostics-plain-output   -maltivec -mvsx -mno-allow-movmisalign
-ftree-vectorize -fno-tree-loop-distribute-patterns -fno-vect-cost-model
-fno-common -O2 -fdump-tree-vect-details -Ofast -fno-tree-scev-cprop -S -o
pr82436.s    (timeout = 300)
spawn -ignore SIGHUP /home/seurer/gcc/git/build/gcc-test/gcc/xgcc
-B/home/seurer/gcc/git/build/gcc-test/gcc/
/home/seurer/gcc/git/gcc-test/gcc/testsuite/gcc.dg/vect/pr82436.c
-fdiagnostics-plain-output -maltivec -mvsx -mno-allow-movmisalign
-ftree-vectorize -fno-tree-loop-distribute-patterns -fno-vect-cost-model
-fno-common -O2 -fdump-tree-vect-details -Ofast -fno-tree-scev-cprop -S -o
pr82436.s
during GIMPLE pass: vect
dump file: pr82436.c.169t.vect
/home/seurer/gcc/git/gcc-test/gcc/testsuite/gcc.dg/vect/pr82436.c: In function
'foo':
/home/seurer/gcc/git/gcc-test/gcc/testsuite/gcc.dg/vect/pr82436.c:20:5:
internal compiler error: Segmentation fault
0x10ba1eeb crash_signal
        /home/seurer/gcc/git/gcc-test/gcc/toplev.c:322
0x10dc5b88 find_uses_to_rename_use
        /home/seurer/gcc/git/gcc-test/gcc/tree-ssa-loop-manip.c:391
0x10dc5b88 find_uses_to_rename_bb
        /home/seurer/gcc/git/gcc-test/gcc/tree-ssa-loop-manip.c:466
0x10dc9623 find_uses_to_rename
        /home/seurer/gcc/git/gcc-test/gcc/tree-ssa-loop-manip.c:498
0x10dc9623 rewrite_into_loop_closed_ssa_1(bitmap_head*, unsigned int, int,
loop*)
        /home/seurer/gcc/git/gcc-test/gcc/tree-ssa-loop-manip.c:664
0x10dc9623 rewrite_into_loop_closed_ssa_1(bitmap_head*, unsigned int, int,
loop*)
        /home/seurer/gcc/git/gcc-test/gcc/tree-ssa-loop-manip.c:629
0x10fabbdb vectorize_loops()
        /home/seurer/gcc/git/gcc-test/gcc/tree-vectorizer.c:1320
0x10def927 execute
        /home/seurer/gcc/git/gcc-test/gcc/tree-ssa-loop.c:413
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
compiler exited with status 1
FAIL: gcc.dg/vect/pr82436.c (internal compiler error)

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[seurer at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

seurer at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |powerpc64-linux-gnu
                 CC|                            |bergner at gcc dot gnu.org,
                   |                            |luoxhu at cn dot ibm.com
              Build|                            |powerpc64-linux-gnu
               Host|                            |powerpc64-linux-gnu

--- Comment #1 from seurer at gcc dot gnu.org ---
commit f35af8df241a9eb9c2edf7da26d3c5f53d6e2511
Author: Xionghu Luo <luoxhu@linux.ibm.com>
Date:   Mon Nov 1 00:12:36 2021 -0500

    Refactor loop_version

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[luoxhu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

luoxhu at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luoxhu at gcc dot gnu.org,
                   |                            |rguenther at suse dot de

--- Comment #2 from luoxhu at gcc dot gnu.org ---
Confirmed.

P7's extra option -mno-allow-movmisalign makes this ICE happens.  If add this
option on P9 also ICEs. Reason is the phi arguments order changes if switch the
sequence of loopify and lv_adjust_loop_entry_edge.

the constant input argument from bb 18 is in phi index 1 now makes the followed
vectorize code fail to handle?

if (_42 != 0)
  goto <bb 18>; [80.00%]
else
  goto <bb 19>; [20.00%]

<bb 18> [local count: 67276368]:

<bb 9> [local count: 611603351]:
# i_76 = PHI <i_57(10), 1(18)>         // here
# y_lsm.6_74 = PHI <_61(10), 0.0(18)>  // here
# w_lsm.7_73 = PHI <_58(10), 0.0(18)>  // here
i.0_72 = (unsigned int) i_76;
_70 = (long unsigned int) i.0_72;
_69 = _70 * 80;
x_68 = r_22(D) + _69;
fpred_67 = x_68->f_pred;
fexp_66 = x_68->f_exp;
tem_65 = fpred_67 - fexp_66;
_64 = x_68->f_sigma;
_63 = tem_65 / _64;
_62 = ABS_EXPR <_63>;
_61 = _62 + y_lsm.6_74;
_60 = tem_65 / fexp_66;
_59 = ABS_EXPR <_60>;
_58 = _59 + w_lsm.7_73;
i_57 = i_76 + 1;
if (n_19(D) > i_57)
  goto <bb 10>; [89.00%]
else
  goto <bb 14>; [11.00%]

<bb 10> [local count: 544326983]:
goto <bb 9>; [100.00%]



It was:


if (_42 != 0)
  goto <bb 18>; [80.00%]
else
  goto <bb 19>; [20.00%]

<bb 18> [local count: 67276368]:

<bb 9> [local count: 611603351]:
# i_76 = PHI <1(18), i_57(10)>   
# y_lsm.6_74 = PHI <0.0(18), _61(10)>
# w_lsm.7_73 = PHI <0.0(18), _58(10)>
i.0_72 = (unsigned int) i_76;
_70 = (long unsigned int) i.0_72;
_69 = _70 * 80;
x_68 = r_22(D) + _69;
fpred_67 = x_68->f_pred;
fexp_66 = x_68->f_exp;
tem_65 = fpred_67 - fexp_66;
_64 = x_68->f_sigma;
_63 = tem_65 / _64;
_62 = ABS_EXPR <_63>;
_61 = _62 + y_lsm.6_74;
_60 = tem_65 / fexp_66;
_59 = ABS_EXPR <_60>;
_58 = _59 + w_lsm.7_73;
i_57 = i_76 + 1;
if (n_19(D) > i_57)
  goto <bb 10>; [89.00%]
else
  goto <bb 20>; [11.00%]

<bb 10> [local count: 544326983]:
goto <bb 9>; [100.00%]


The comments in function gimple_lv_adjust_loop_header_phi says 

  /* Browse all 'second' basic block phi nodes and add phi args to
     edge 'e' for 'first' head. PHI args are always in correct order.  */ 

Any function to fix the phi order?

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[luoxhu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

--- Comment #3 from luoxhu at gcc dot gnu.org ---
This hack could restore the previous phi order to put nondfs phi args before
dfs_edge args.  But I am not sure whether this is the correct direction.  At
least  it proves that the phi order matters for later vectorizer code.


diff --git a/gcc/cfgloopmanip.c b/gcc/cfgloopmanip.c
index 455c3ef8db9..2ca256c15fa 100644
--- a/gcc/cfgloopmanip.c
+++ b/gcc/cfgloopmanip.c
@@ -31,6 +31,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimplify-me.h"
 #include "tree-ssa-loop-manip.h"
 #include "dumpfile.h"
+#include "ssa.h"

 static void copy_loops_to (class loop **, int,
                           class loop *);
@@ -1577,6 +1578,41 @@ lv_adjust_loop_entry_edge (basic_block first_head,
basic_block second_head,
   e1->probability = then_prob;
   e->probability = else_prob;

+  edge le, dfs = NULL, nondfs = NULL;
+  edge_iterator ei;
+
+  if (EDGE_COUNT (e1->dest->preds) > 1)
+  {
+    FOR_EACH_EDGE (le, ei, e1->dest->preds)
+      {
+       if (le->flags & EDGE_DFS_BACK)
+         dfs = le;
+       else
+         nondfs = le;
+      }
+    if (dfs && nondfs && dfs->dest_idx < nondfs->dest_idx)
+      {
+       gphi_iterator psi;
+       gphi *phi;
+       tree dfsdef, nondfsdef;
+       for (psi = gsi_start_phis (e1->dest); !gsi_end_p (psi); gsi_next
(&psi))
+         {
+           phi = psi.phi ();
+           dfsdef = PHI_ARG_DEF (phi, dfs->dest_idx);
+           nondfsdef = PHI_ARG_DEF (phi, nondfs->dest_idx);
+           SET_PHI_ARG_DEF (phi, dfs->dest_idx, nondfsdef);
+           SET_PHI_ARG_DEF (phi, nondfs->dest_idx, dfsdef);
+         }
+
+       EDGE_PRED (e1->dest, dfs->dest_idx) = nondfs;
+       EDGE_PRED (e1->dest, nondfs->dest_idx) = dfs;
+
+       unsigned int temp = nondfs->dest_idx;
+       nondfs->dest_idx = dfs->dest_idx;
+       dfs->dest_idx = temp;
+      }
+  }
+

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-11-02
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
   Target Milestone|---                         |12.0
     Ever confirmed|0                           |1

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Let me have a look here.

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
The gimple_lv_adjust_loop_header_phi comment isn't relevant but what is is the
association between PHI node argument and SLP node index from the analysis
phase,
in particular for backedges.  See vect_schedule_scc which does

  /* Now fixup the backedge def of the vectorized PHIs in this SCC.  */
  slp_tree phi_node;
  FOR_EACH_VEC_ELT (phis_to_fixup, i, phi_node)
    {
      gphi *phi = as_a <gphi *> (SLP_TREE_REPRESENTATIVE (phi_node)->stmt);
      edge_iterator ei;
      edge e;
      FOR_EACH_EDGE (e, ei, gimple_bb (phi)->preds)
        {
          unsigned dest_idx = e->dest_idx;
          child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
          if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
            continue;

but here

(gdb) p e
$14 = <edge 0x7ffff63c0690 (10 -> 9)>
(gdb) p e->dest_idx
$12 = 0
(gdb) p debug (phi_node)
pr82436.c:20:5: note: node 0x3448ba8 (max_nunits=2, refcnt=1)
pr82436.c:20:5: note: op template: w_lsm.7_73 = PHI <_58(10), 0.0(25)>
pr82436.c:20:5: note:   stmt 0 w_lsm.7_73 = PHI <_58(10), 0.0(25)>
pr82436.c:20:5: note:   stmt 1 y_lsm.6_74 = PHI <_61(10), 0.0(25)>
pr82436.c:20:5: note:   children (nil) 0x34487f0

so in fact the entry edge edge now has the backedge SLP node.

I think the former dance redirecting edges back and forth made the edge
order consistent but nothing really forced it the same order as the
original loop which could have either order as well.

In fact the old code seems to reliably put the entry edge first
(but we start with the entry edge second with the very first version)
but the new code manages to swap the edges on the _old_ loop
which I think is something we should try to avoid.

That happens when we loop_redirect_edge (latch_edge, nloop->header);

I suppose without making loop_version entirely SSA dependent we can
for the moment mostly ensure we end up with the same order but not
necessarily avoid changing the original IL order.

diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index 8ed8c69b5b1..81b0dcb7006 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -9044,6 +9044,23 @@ gimple_lv_adjust_loop_header_phi (basic_block first,
basic_block second,
       def = PHI_ARG_DEF (phi2, e2->dest_idx);
       add_phi_arg (phi1, def, e, gimple_phi_arg_location_from_edge (phi2,
e2));
     }
+
+  /* If the edges into the old and new loop end up at different PHI arg
+     indices swap one by redirecting it to its own destination.  */
+  if (e->dest_idx != e2->dest_idx)
+    {
+      if (e->dest_idx == 0)
+       {
+         ssa_redirect_edge (e, e->dest);
+         flush_pending_stmts (e);
+       }
+      else
+       {
+         gcc_assert (e2->dest_idx == 0);
+         ssa_redirect_edge (e2, e2->dest);
+         flush_pending_stmts (e2);
+       }
+    }
 }

ensures this and fixes the testcase.  As said it would be desirable to
preserve the original loop PHI argument order.

A way to have the vectorizer less fragile would of course be also appreciated.

I am testing the above.

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:164bbf701ff10ff44e272525e8f462ed3ff1cf43

commit r12-4850-g164bbf701ff10ff44e272525e8f462ed3ff1cf43
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Nov 2 18:47:14 2021 +0100

    tree-optimization/103029 - ensure vect loop versioning constraint on PHIs

    PHI nodes in vectorizer loop versioning need to maintain the same
    order of PHI arguments to not disturb SLP discovery.  The following
    adds an assertion and mitigation in case loop versioning breaks this
    which happens more often after the recent reorg.

    2021-11-02  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/103029
            * tree-vect-loop-manip.c (vect_loop_versioning): Ensure
            the PHI nodes in the loop maintain their original operand
            order.

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

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

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

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Should be fixed now.

[Bug tree-optimization/103029] [12 regression] gcc.dg/vect/pr82436.c ICEs on r12-4818

[luoxhu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103029

luoxhu at gcc dot gnu.org changed:

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

--- Comment #8 from luoxhu at gcc dot gnu.org ---
*** Bug 103041 has been marked as a duplicate of this bug. ***