[Bug fortran/71807] New: Internal compiler error with NULL() reference in structure constructor

[ian_harvey at bigpond dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71807

            Bug ID: 71807
           Summary: Internal compiler error with NULL() reference in
                    structure constructor
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ian_harvey at bigpond dot com
  Target Milestone: ---

The following snippet, when compiled with gfortran recent trunk (r238061) or
6.1.1 results in an internal compiler error.

~~

MODULE fold_convert_loc_ice
  IMPLICIT NONE
  PRIVATE

  TYPE, PUBLIC :: ta
    PRIVATE
    INTEGER :: a_comp
  END TYPE ta

  TYPE, PUBLIC :: tb
    TYPE(ta), ALLOCATABLE :: b_comp
  END TYPE tb
CONTAINS
  SUBROUTINE proc
    TYPE(tb) :: b

    b = tb(null())
  END SUBROUTINE proc
END MODULE fold_convert_loc_ice

~~

$ gfortran -c -v fold_convert_loc_ice.f90
Using built-in specs.
COLLECT_GCC=gfortran
Target: x86_64-pc-linux-gnu
Configured with: .././src/configure --prefix=/home/MEGMS2/ian/usr/gcc-7.0.0
--enable-languages=c,c++,fortran --enable-libgomp --enable-checking=release
Thread model: posix
gcc version 7.0.0 20160706 (experimental) (GCC)
COLLECT_GCC_OPTIONS='-c' '-v' '-mtune=generic' '-march=x86-64'
 /home/MEGMS2/ian/usr/gcc-7.0.0/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/f951
fold_convert_loc_ice.f90 -quiet -dumpbase fold_convert_loc_ice.f90
-mtune=generic -march=x86-64 -auxbase fold_convert_loc_ice -version
-fintrinsic-modules-path
/home/MEGMS2/ian/usr/gcc-7.0.0/lib/gcc/x86_64-pc-linux-gnu/7.0.0/finclude -o
/tmp/cc3kuTzv.s
GNU Fortran (GCC) version 7.0.0 20160706 (experimental) (x86_64-pc-linux-gnu)
        compiled by GNU C version 7.0.0 20160704 (experimental), GMP version
6.1.0, MPFR version 3.1.4, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU Fortran2008 (GCC) version 7.0.0 20160706 (experimental)
(x86_64-pc-linux-gnu)
        compiled by GNU C version 7.0.0 20160704 (experimental), GMP version
6.1.0, MPFR version 3.1.4, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
fold_convert_loc_ice.f90:17:0:

     b = tb(null())

internal compiler error: in fold_convert_loc, at fold-const.c:2371
0x833153 fold_convert_loc(unsigned int, tree_node*, tree_node*)
        ../.././src/gcc/fold-const.c:2371
0x6b6e27 gfc_trans_subcomponent_assign
        ../.././src/gcc/fortran/trans-expr.c:7250
0x6b6653 gfc_trans_structure_assign(tree_node*, gfc_expr*, bool)
        ../.././src/gcc/fortran/trans-expr.c:7391
0x6b7dbf gfc_conv_structure(gfc_se*, gfc_expr*, int)
        ../.././src/gcc/fortran/trans-expr.c:7420
0x6b8e62 gfc_trans_assignment_1
        ../.././src/gcc/fortran/trans-expr.c:9317
0x682275 trans_code
        ../.././src/gcc/fortran/trans.c:1678
0x6a6019 gfc_generate_function_code(gfc_namespace*)
        ../.././src/gcc/fortran/trans-decl.c:6202
0x685a39 gfc_generate_module_code(gfc_namespace*)
        ../.././src/gcc/fortran/trans.c:2056
0x63d2eb translate_all_program_units
        ../.././src/gcc/fortran/parse.c:5873
0x63d2eb gfc_parse_file()
        ../.././src/gcc/fortran/parse.c:6092
0x67ec62 gfc_be_parse_file
        ../.././src/gcc/fortran/f95-lang.c:198
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