[Bug tree-optimization/114832] New: ICE at -O{2,3} with "-fno-tree-loop-if-convert -fno-tree-loop-distribute-patterns -ftree-vectorize" on x86_64-linux-gnu: in verify_dominators, at dominance.cc:1194

[Bug tree-optimization/114832] New: ICE at -O{2,3} with "-fno-tree-loop-if-convert -fno-tree-loop-distribute-patterns -ftree-vectorize" on x86_64-linux-gnu: in verify_dominators, at dominance.cc:1194

[zhendong.su at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114832

            Bug ID: 114832
           Summary: ICE at -O{2,3} with "-fno-tree-loop-if-convert
                    -fno-tree-loop-distribute-patterns -ftree-vectorize"
                    on x86_64-linux-gnu: in verify_dominators, at
                    dominance.cc:1194
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhendong.su at inf dot ethz.ch
  Target Milestone: ---

It appears to be a recent regression and does not reproduce with 13.2 and
earlier.

Compiler Explorer: https://godbolt.org/z/1do4bc9W7


[515] % gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/local/suz-local/software/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/14.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--enable-checking=yes --prefix=/local/suz-local/software/local/gcc-trunk
--enable-sanitizers --enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.1 20240423 (experimental) (GCC) 
[516] % 
[516] % gcctk -c -O2 -fno-tree-loop-if-convert
-fno-tree-loop-distribute-patterns -ftree-vectorize small.c 
small.c: In function ‘e’:
small.c:2:6: error: dominator of 6 should be 13, not 5
    2 | void e() {
      |      ^
during GIMPLE pass: vect
small.c:2:6: internal compiler error: in verify_dominators, at
dominance.cc:1194
0x7a1828 verify_dominators(cdi_direction)
        ../../gcc-trunk/gcc/dominance.cc:1194
0x145a0d0 checking_verify_dominators(cdi_direction)
        ../../gcc-trunk/gcc/dominance.h:76
0x145a0d0 slpeel_tree_duplicate_loop_to_edge_cfg(loop*, edge_def*, loop*,
edge_def*, edge_def*, edge_def**, bool, vec<basic_block_def*, va_heap,
vl_ptr>*)
        ../../gcc-trunk/gcc/tree-vect-loop-manip.cc:1961
0x145d46c vect_do_peeling(_loop_vec_info*, tree_node*, tree_node*, tree_node**,
tree_node**, tree_node**, int, bool, bool, tree_node**)
        ../../gcc-trunk/gcc/tree-vect-loop-manip.cc:3444
0x144cd58 vect_transform_loop(_loop_vec_info*, gimple*)
        ../../gcc-trunk/gcc/tree-vect-loop.cc:11910
0x149374e vect_transform_loops
        ../../gcc-trunk/gcc/tree-vectorizer.cc:1006
0x1493e53 try_vectorize_loop_1
        ../../gcc-trunk/gcc/tree-vectorizer.cc:1152
0x1493e53 try_vectorize_loop
        ../../gcc-trunk/gcc/tree-vectorizer.cc:1182
0x149448c execute
        ../../gcc-trunk/gcc/tree-vectorizer.cc:1298
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
[517] % 
[517] % cat small.c
int a, b, c, d[3];
void e() {
  int f, g = 0;
  for (; g < 3; g++) {
    if (f || a || b && c) {
      int h, *i = &h, **j = &i;
    }
    d[g] = 0;
  }
}

[Bug tree-optimization/114832] [14 Regression] ICE at -O{2,3} with "-fno-tree-loop-if-convert -fno-tree-loop-distribute-patterns -ftree-vectorize" on x86_64-linux-gnu: in verify_dominators, at dominance.cc:1194

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114832

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|ICE at -O{2,3} with         |[14 Regression] ICE at
                   |"-fno-tree-loop-if-convert  |-O{2,3} with
                   |-fno-tree-loop-distribute-p |"-fno-tree-loop-if-convert
                   |atterns -ftree-vectorize"   |-fno-tree-loop-distribute-p
                   |on x86_64-linux-gnu: in     |atterns -ftree-vectorize"
                   |verify_dominators, at       |on x86_64-linux-gnu: in
                   |dominance.cc:1194           |verify_dominators, at
                   |                            |dominance.cc:1194
   Target Milestone|---                         |14.0
      Known to fail|                            |14.0
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-04-24
      Known to work|                            |13.2.0
           Keywords|                            |ice-checking

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. ICE does not happen with -fno-checking so adding ice-checking.

[Bug tree-optimization/114832] [14 Regression] ICE at -O{2,3} with "-fno-tree-loop-if-convert -fno-tree-loop-distribute-patterns -ftree-vectorize" on x86_64-linux-gnu: in verify_dominators, at dominance.cc:1194

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114832

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> Confirmed. ICE does not happen with -fno-checking so adding ice-checking.

Also GCC 13.2.0 didn't ICE with -fchecking either.

[Bug tree-optimization/114832] [14 Regression] ICE at -O{2,3} with "-fno-tree-loop-if-convert -fno-tree-loop-distribute-patterns -ftree-vectorize" on x86_64-linux-gnu: in verify_dominators, at dominance.cc:1194

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114832

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

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

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
With the early break code we now allow multiple blocks in the loop body but
guess this only happens for blocks with exits.  In this case we have a simple
forwarder which seems to confuse the code.  Usually if-conversion gets rid of
those so -fno-tree-loop-if-convert is critical to trigger this.

If we want to fix this on the release branch I think we should reject loops
with this kind of CFG again.  In stage1 we should fix the real issue.

I think the fix is just

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 8d9b533d50f..43c7881c640 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1523,7 +1523,7 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop,
edge loop_exit,

   exit_dest = exit->dest;
   was_imm_dom = (get_immediate_dominator (CDI_DOMINATORS,
-                                         exit_dest) == loop->header ?
+                                         exit_dest) == exit->src ?
                 true : false);

   /* Also copy the pre-header, this avoids jumping through hoops to

[Bug tree-optimization/114832] [14 Regression] ICE at -O{2,3} with "-fno-tree-loop-if-convert -fno-tree-loop-distribute-patterns -ftree-vectorize" on x86_64-linux-gnu: in verify_dominators, at dominance.cc:1194

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114832

--- Comment #4 from GCC 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:e28e8ab1a92e9b49f7c4045377577c8dc17751b7

commit r14-10105-ge28e8ab1a92e9b49f7c4045377577c8dc17751b7
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Apr 24 06:24:22 2024 +0200

    tree-optimization/114832 - wrong dominator info with vect peeling

    When we update the dominator of the redirected exit after peeling
    we check whether the immediate dominator was the loop header rather
    than the exit source when we later want to just update it to the
    new source.  The following fixes this oversight.

            PR tree-optimization/114832
            * tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
            Fix dominance check.

            * gcc.dg/vect/pr114832.c: New testcase.

[Bug tree-optimization/114832] [14 Regression] ICE at -O{2,3} with "-fno-tree-loop-if-convert -fno-tree-loop-distribute-patterns -ftree-vectorize" on x86_64-linux-gnu: in verify_dominators, at dominance.cc:1194

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114832

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED
            Version|unknown                     |14.0

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.