With option -fcoarray=single, affects versions down to at least r5 :
(compiles with -fcoarray=lib)
(compiles always without attribute volatile)


$ cat z1.f90
program p
   integer, volatile :: a = 1
   integer, volatile :: b[*] = 1
   if (a /= b) stop
end


$ gfortran-11-20210418 -c z1.f90 -fcoarray=lib
$
$ gfortran-11-20210418 -c z1.f90 -fcoarray=single
z1.f90:5:3:

    5 | end
      |   1
internal compiler error: Segmentation fault
0xc0b22f crash_signal
        ../../gcc/toplev.c:327
0x7425b1 gfc_trans_array_cobounds(tree_node*, stmtblock_t*, gfc_symbol const*)
        ../../gcc/fortran/trans-array.c:6257
0x75e271 gfc_trans_deferred_vars(gfc_symbol*, gfc_wrapped_block*)
        ../../gcc/fortran/trans-decl.c:4858
0x75fe22 gfc_generate_function_code(gfc_namespace*)
        ../../gcc/fortran/trans-decl.c:6988
0x6e66b6 translate_all_program_units
        ../../gcc/fortran/parse.c:6351
0x6e66b6 gfc_parse_file()
        ../../gcc/fortran/parse.c:6620
0x7329cf gfc_be_parse_file
        ../../gcc/fortran/f95-lang.c:212