[Bug tree-optimization/103458] New: [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree)

[Bug tree-optimization/103458] New: [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree)

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

            Bug ID: 103458
           Summary: [12 Regression] ICE in verify_loop_structure, at
                    cfgloop.c:1736 (error: loop with header 4 not in loop
                    tree)
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

gcc-12.0.0-alpha20211121 snapshot (g:da17c304e22ba256eba0b03710aa329115163b08)
ICEs when compiling the following testcase w/ -O2:

__attribute__ ((returns_twice)) int
bar (void);

void
foo (int *p, int x)
{
  *p = 0;
  while (*p < 1)
    {
      x = 0;
      while (x < 1)
        bar ();

      x /= 0;
    }

  foo (p, x);
}

% gcc-12.0.0 -O2 -w -c xiksrvsw.c
xiksrvsw.c: In function 'foo':
xiksrvsw.c:5:1: error: loop with header 4 not in loop tree
    5 | foo (int *p, int x)
      | ^~~
during GIMPLE pass: cddce
xiksrvsw.c:5:1: internal compiler error: in verify_loop_structure, at
cfgloop.c:1736
0x6816e7 verify_loop_structure()
       
/var/tmp/portage/sys-devel/gcc-12.0.0_alpha20211121/work/gcc-12-20211121/gcc/cfgloop.c:1736
0xdb8457 execute_function_todo
       
/var/tmp/portage/sys-devel/gcc-12.0.0_alpha20211121/work/gcc-12-20211121/gcc/passes.c:2058
0xdb8cbe execute_todo
       
/var/tmp/portage/sys-devel/gcc-12.0.0_alpha20211121/work/gcc-12-20211121/gcc/passes.c:2096

[Bug tree-optimization/103458] [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0

[Bug tree-optimization/103458] [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
           Keywords|                            |needs-bisection
   Last reconfirmed|                            |2021-11-29
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. It looks like a latent bug though.

[Bug tree-optimization/103458] [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

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

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

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I will have a look.

[Bug tree-optimization/103458] [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue is that we have


   bb3:<-\ <--\
    |\   /    |
    | --      |
    |         |
   bb4:       |
    .ABNORMAL_DISPATCHER

at the start of CDDCE and the abnormal predecessor makes us not consider BB3
a loop header.  But then we have an opportunity to create a forwarder
(we avoid creating them for loop headers but this isn't one ...) which
shows the opportunity to represent this CFG as an outer loop with an inner
cycle with abnormal edge.  CFG cleanup doesn't undo this forwarder because
there are virtual PHIs in it.

ethread is the pass that introduces this problematic header while this is
all inside an irreducible region.

In principle handling the abnormal edge in this case would be OK but in
general abnormal latches pose a problem since with several loop opts we
are facing the need to split/redirect those so relaxing this condition
doesn't look feasible (but it creates nicer CFG for this particular testcase).

[Bug tree-optimization/103458] [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree) since r12-5301-g045206450386bcd7

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-bisection             |
            Summary|[12 Regression] ICE in      |[12 Regression] ICE in
                   |verify_loop_structure, at   |verify_loop_structure, at
                   |cfgloop.c:1736 (error: loop |cfgloop.c:1736 (error: loop
                   |with header 4 not in loop   |with header 4 not in loop
                   |tree)                       |tree) since
                   |                            |r12-5301-g045206450386bcd7
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #4 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r12-5301-g045206450386bcd7.

[Bug tree-optimization/103458] [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree) since r12-5301-g045206450386bcd7

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

--- Comment #5 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:85e91ad55a69282c1b0e34569836a026a1a954d1

commit r12-5572-g85e91ad55a69282c1b0e34569836a026a1a954d1
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Nov 29 09:15:47 2021 +0100

    tree-optimization/103458 - avoid creating new loops in CD-DCE

    When creating forwarders in CD-DCE we have to avoid creating loops
    where we formerly did not consider those because of abnormal
    predecessors.  At this point simply excuse us when there are any
    abnormal predecessors.

    2021-11-29  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/103458
            * tree-ssa-dce.c (make_forwarders_with_degenerate_phis): Do not
            create forwarders for blocks with abnormal predecessors.

            * gcc.dg/torture/pr103458.c: New testcase.

[Bug tree-optimization/103458] [12 Regression] ICE in verify_loop_structure, at cfgloop.c:1736 (error: loop with header 4 not in loop tree) since r12-5301-g045206450386bcd7

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103458

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

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

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.