[Bug tree-optimization/98845] New: [8/9/10 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.)

[Bug tree-optimization/98845] New: [8/9/10 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.)

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

            Bug ID: 98845
           Summary: [8/9/10 Regression] ICE: SSA corruption (Unable to
                    coalesce ssa_names 2 and 23 which are marked as MUST
                    COALESCE.)
           Product: gcc
           Version: 11.0
            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-11.0.0-alpha20210124 snapshot (g:6b1633378b74bed1d999a0ae2549088515a30ba0)
ICEs when compiling the following testcase w/ -Os -fno-tree-dce:

int __attribute__ ((returns_twice))
func_58 (int);

int
func_215 (int func_215___trans_tmp_2, int g_180, int p_217, int p_218)
{
  if (func_215___trans_tmp_2)
    func_215 (0, 0, 0, 0);
  else if (g_180)
    {
      if (p_218)
        return 1;

      p_218 = p_217;
    }
  else
    {
      p_217 = 0;
      while (!p_217)
        {
        }
    }

  p_218 = 0;
  while (p_218)
    {
      func_58 (p_217);
      func_58 (p_217 + 1);
    }

  return 0;
}

% gcc-11.0.0 -Os -fno-tree-dce -c gdh96e2t.c

Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.
p_217_2(ab) and  p_217_23(D)(ab)
during RTL pass: expand
gdh96e2t.c: In function 'func_215':
gdh96e2t.c:5:1: internal compiler error: SSA corruption
    5 | func_215 (int func_215___trans_tmp_2, int g_180, int p_217, int p_218)
      | ^~~~~~~~
0xf1d345 fail_abnormal_edge_coalesce
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20210124/work/gcc-11-20210124/gcc/tree-ssa-coalesce.c:1003
0xf1d345 coalesce_partitions
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20210124/work/gcc-11-20210124/gcc/tree-ssa-coalesce.c:1425
0xf1d345 coalesce_ssa_name(_var_map*)
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20210124/work/gcc-11-20210124/gcc/tree-ssa-coalesce.c:1755
0xeb8fcc remove_ssa_form
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20210124/work/gcc-11-20210124/gcc/tree-outof-ssa.c:1065
0xeb8fcc rewrite_out_of_ssa(ssaexpand*)
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20210124/work/gcc-11-20210124/gcc/tree-outof-ssa.c:1323
0x961e60 execute
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20210124/work/gcc-11-20210124/gcc/cfgexpand.c:6533

[Bug tree-optimization/98845] [8/9/10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection
   Target Milestone|---                         |8.5
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-01-27
           Priority|P3                          |P2
             Status|UNCONFIRMED                 |ASSIGNED
            Summary|[8/9/10 Regression] ICE:    |[8/9/10/11 Regression] ICE:
                   |SSA corruption (Unable to   |SSA corruption (Unable to
                   |coalesce ssa_names 2 and 23 |coalesce ssa_names 2 and 23
                   |which are marked as MUST    |which are marked as MUST
                   |COALESCE.)                  |COALESCE.)
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug tree-optimization/98845] [8/9/10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-bisection             |
            Summary|[8/9/10/11 Regression] ICE: |[8/9/10/11 Regression] ICE:
                   |SSA corruption (Unable to   |SSA corruption (Unable to
                   |coalesce ssa_names 2 and 23 |coalesce ssa_names 2 and 23
                   |which are marked as MUST    |which are marked as MUST
                   |COALESCE.)                  |COALESCE.) since
                   |                            |r6-528-g465770e43996a132
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r6-528-g465770e43996a132.

[Bug tree-optimization/98845] [8/9/10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Looks like tail merging triggers this.

[Bug tree-optimization/98845] [8/9/10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
+find_duplicates: <bb 6> duplicate of <bb 20>
+Removing basic block 20

@@ -170,7 +180,7 @@
   <bb 17> [local count: 3614577]:
   goto <bb 13>; [100.00%]

-  <bb 6> [local count: 7016531]:
+  <bb 6> [local count: 8742389]:
   p_218_24 = p_217_23(D)(ab);
   p_217_32 = p_217_23(D)(ab);
   goto <bb 13>; [100.00%]
@@ -213,12 +223,10 @@
   if (p_218_8 != 0)
     goto <bb 19>; [83.51%]
   else
-    goto <bb 20>; [16.49%]
-
-  <bb 20> [local count: 1725858]:
+    goto <bb 6>; [16.49%]

   <bb 13> [local count: 12356965]:
-  # _9 = PHI <1(17), 0(20), 0(6)>
+  # _9 = PHI <1(17), 0(6)>
   return _9;

but that makes _23(D) live on the path from bb 12 to bb 13.  The issue here
is that _23 and _32 are unused but their RHS is still accounted for during
LIVE problem solving but they are ignored during VN and by tail-merging
which just looks at BB side-effects.

So the testcase is really an artifact of -fno-tree-dce.

One could argue that tail merging should treat a use of abnormals as
side-effect but I think that won't play well with its structure.

[Bug tree-optimization/98845] [9/10/11/12 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug tree-optimization/98845] [9/10/11/12 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

--- Comment #6 from Arseny Solokha <asolokha at gmx dot com> ---
gcc-12.0.0-alpha20210530 snapshot (g:a0a7adeea31918deefb053a9a15257af94aecfaf)
compiles the testcase w/o ICE.

[Bug tree-optimization/98845] [9/10/11/12 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

--- Comment #7 from Martin Liška <marxin at gcc dot gnu.org> ---
Fixed on master with r12-248-gb58dc0b803057c0e.

[Bug tree-optimization/98845] [9/10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 31 May 2021, marxin at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845
> 
> --- Comment #7 from Martin Liška <marxin at gcc dot gnu.org> ---
> Fixed on master with r12-248-gb58dc0b803057c0e.

Yeah, not "fixed" but worked around.

[Bug tree-optimization/98845] [9/10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug tree-optimization/98845] [9/10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
*** Bug 104947 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/98845] [9/10/11/12 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

Arseny Solokha <asolokha at gmx dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[9/10/11 Regression] ICE:   |[9/10/11/12 Regression]
                   |SSA corruption (Unable to   |ICE: SSA corruption (Unable
                   |coalesce ssa_names 2 and 23 |to coalesce ssa_names 2 and
                   |which are marked as MUST    |23 which are marked as MUST
                   |COALESCE.) since            |COALESCE.) since
                   |r6-528-g465770e43996a132    |r6-528-g465770e43996a132

--- Comment #11 from Arseny Solokha <asolokha at gmx dot com> ---
It should be labeled [12 Regression] again, then, as the issue is still there
on trunk.

[Bug tree-optimization/98845] [9/10/11/12 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Arseny Solokha from comment #11)
> It should be labeled [12 Regression] again, then, as the issue is still
> there on trunk.

 w/ -O2 -fno-tree-dce -fno-tree-dse (possibly with -fno-tree-dse also for the
testcase in the description)

int n;

__attribute__ ((returns_twice)) void
foo (void);

void
bar (void);

void
quux (int x)
{
  if (x)
    ++x;
  else
    {
      if (n)
        {
          x = 1;
          foo ();
        }
      else
        bar ();

      if (n)
        {
          ++x;
          ++n;
        }
    }
}

[Bug tree-optimization/98845] [10/11/12/13 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.5                         |10.4

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed

[Bug tree-optimization/98845] [10/11/12/13 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug tree-optimization/98845] [11/12/13/14 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST COALESCE.) since r6-528-g465770e43996a132

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98845

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.