[Bug lto/84592] New: [openacc] lto1: ICE in input_varpool_node, at lto-cgraph.c:1424: for CSWTCH symbol

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84592

            Bug ID: 84592
           Summary: [openacc] lto1: ICE in input_varpool_node, at
                    lto-cgraph.c:1424: for CSWTCH symbol
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

Consider the following openacc testcase:
...
/* { dg-additional-options "-ftree-switch-conversion" } */

#include <stdio.h>

#pragma acc routine seq
static int __attribute__((noinline)) foo (int n)
{
  switch (n & 3)
    {
    case 0: return 4;
    case 1: return 3;
    case 2: return 2;
    default:
      return 1;
    }
}

int
main (void)
{
  int n[1];
  n[1] = 4;
#pragma acc parallel copy(n)
  {
    n[0] = foo (n[0]); 
  }
  printf ("n: %d\n", n[0]);

  return 0;
}
...

When compiling this (by copying it into
libgomp/testsuite/libgomp.oacc-c-c++-common), we run into:
...
lto1: internal compiler error: in input_varpool_node, at lto-cgraph.c:1424^M
0x959ebb input_varpool_node^M
        gcc/lto-cgraph.c:1422^M
0x959ebb input_cgraph_1^M
        gcc/lto-cgraph.c:1544^M
0x959ebb input_symtab()^M
        gcc/lto-cgraph.c:1858^M
0x5aceac read_cgraph_and_symbols^M
        gcc/lto/lto.c:2891^M
0x5aceac lto_main()^M
        gcc/lto/lto.c:3356^M
...

When running lto1 using gdb we find the node we're processing is:
...
(gdb) call debug_generic_expr ( node.decl )
CSWTCH.4
...

The CSWTCH.4 is a symbol introduced by -ftree-switch-conversion. If we use
-fno-tree-switch-conversion there's no ICE.