[Bug tree-optimization/96349] New: [10/11 Regression] ICE: SSA corruption (Unable to coalesce ssa_names 2 and 3 which are marked as MUST COALESCE.) [in fail_abnormal_edge_coalesce]

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96349

            Bug ID: 96349
           Summary: [10/11 Regression] ICE: SSA corruption (Unable to
                    coalesce ssa_names 2 and 3 which are marked as MUST
                    COALESCE.) [in fail_abnormal_edge_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-alpha20200726 snapshot (g:39ddfef9a5c24acf6412236f52f6716c8e0ebc9e)
ICEs when compiling the following testcase w/ -O3:

void __attribute__ ((returns_twice))
gr (void);

void
ib (void);

void
zg (void);

void
yw (int uz)
{
  gr ();

  for (;;)
    if (uz != 0)
      {
        uz = 0;
        ib ();
      }
    else
      zg ();
}

% gcc-11.0.0 -O3 -c kl7mlgao.c

Unable to coalesce ssa_names 2 and 3 which are marked as MUST COALESCE.
uz_2(ab) and  uz_3(ab)
during RTL pass: expand
kl7mlgao.c: In function 'yw':
kl7mlgao.c:11:1: internal compiler error: SSA corruption
   11 | yw (int uz)
      | ^~
0xedadfa fail_abnormal_edge_coalesce
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20200726/work/gcc-11-20200726/gcc/tree-ssa-coalesce.c:1003
0xedadfa coalesce_partitions
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20200726/work/gcc-11-20200726/gcc/tree-ssa-coalesce.c:1425
0xedadfa coalesce_ssa_name(_var_map*)
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20200726/work/gcc-11-20200726/gcc/tree-ssa-coalesce.c:1755
0xe78937 remove_ssa_form
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20200726/work/gcc-11-20200726/gcc/tree-outof-ssa.c:1065
0xe78937 rewrite_out_of_ssa(ssaexpand*)
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20200726/work/gcc-11-20200726/gcc/tree-outof-ssa.c:1323
0x912f80 execute
       
/var/tmp/portage/sys-devel/gcc-11.0.0_alpha20200726/work/gcc-11-20200726/gcc/cfgexpand.c:6377