[Bug fortran/78990] New: ICE when assigning polymorphic array function result

["cmacmackin at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78990

            Bug ID: 78990
           Summary: ICE when assigning polymorphic array function result
           Product: gcc
           Version: 6.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cmacmackin at gmail dot com
  Target Milestone: ---

Created attachment 40459
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40459&action=edit
Minimal reproducer

When a function returns a polymorphic array which is to be assigned to a local
array (via defined assignment), gfortran experiences a segfault. I've attached
a minimal example, which produces an ICE in gfortran 6.2.0 and 5.4.1 (both from
the Ubuntu 16.04 repos, the former from the ubuntu-toolchain-r/test PPA). The
error message is as follows:

minimal.f90:36:0:

   v3 = return_t1(v1)

internal compiler error: Segmentation fault
0xa71b9f crash_signal
        ../../src/gcc/toplev.c:333
0x696d84 gfc_conv_array_stride(tree_node*, int)
        ../../src/gcc/fortran/trans-array.c:2776
0x696d84 gfc_trans_preloop_setup
        ../../src/gcc/fortran/trans-array.c:3528
0x69793a gfc_start_scalarized_body(gfc_loopinfo*, stmtblock_t*)
        ../../src/gcc/fortran/trans-array.c:3586
0x6ed5cf gfc_trans_call(gfc_code*, bool, tree_node*, tree_node*, bool)
        ../../src/gcc/fortran/trans-stmt.c:476
0x68ef73 trans_code
        ../../src/gcc/fortran/trans.c:1768
0x6b25dc gfc_generate_function_code(gfc_namespace*)
        ../../src/gcc/fortran/trans-decl.c:6167
0x64a800 translate_all_program_units
        ../../src/gcc/fortran/parse.c:5915
0x64a800 gfc_parse_file()
        ../../src/gcc/fortran/parse.c:6121
0x68c1c2 gfc_be_parse_file
        ../../src/gcc/fortran/f95-lang.c:201
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-6/README.Bugs> for instructions.

Note that I'm not 100% certain that this is legal code (I don't have access to
any other compilers to check).