[Bug target/84028] New: [nvptx] nested-function-1.f90 hangs at -O1

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84028

            Bug ID: 84028
           Summary: [nvptx] nested-function-1.f90 hangs at -O1
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

These openacc fails are left on trunk:
...
WARNING: program timed out.
FAIL: libgomp.oacc-fortran/nested-function-1.f90 -DACC_DEVICE_TYPE_nvidia=1
-DACC_MEM_SHARED=0  -O1  execution test
WARNING: program timed out.
FAIL: libgomp.oacc-fortran/nested-function-1.f90 -DACC_DEVICE_TYPE_nvidia=1
-DACC_MEM_SHARED=0  -O2  execution test
FAIL: libgomp.oacc-fortran/nested-function-1.f90 -DACC_DEVICE_TYPE_nvidia=1
-DACC_MEM_SHARED=0  -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops
-ftracer -finline-functions  execution test
FAIL: libgomp.oacc-fortran/nested-function-1.f90 -DACC_DEVICE_TYPE_nvidia=1
-DACC_MEM_SHARED=0  -O3 -g  execution test
...

This minimal test-case hangs at GOMP_NVPTX_JIT=-O1 and higher:
...
program foo
  integer :: a(3,3,3), k, kk, kkk, l, ll, lll

  a = 1

  !$acc parallel num_gangs(1) num_workers(2)

  if (any(a(1:3,1:3,1:3).ne.1)) call abort

  do ll=1,1
     !$acc loop vector
     do lll=1,1
        a(1,1,1) = 2
     enddo
  enddo

  if (a(1,1,1).ne.2) call abort

  !$acc end parallel

end program foo
...

We generate for the abort:
...
$L4:
@ %r56 bra.uni $L27;
@ %r57 bra $L28;
{
  call _gfortran_abort;
  trap;
  exit;
}
$L28:
exit;
$L27:
...

This is similar to PR81352, but for workers. The neutered workers start
executing random code after $L27.