[Bug fortran/81898] New: Issue with polymorphic container class

["jdhughes at usgs dot gov" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81898

            Bug ID: 81898
           Summary: Issue with polymorphic container class
           Product: gcc
           Version: 7.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jdhughes at usgs dot gov
  Target Milestone: ---

Created attachment 42006
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42006&action=edit
Offending code

The attached code is a minimal example of a problem we have encountered
compiling one of our software products with version 7.1.1. The compiled code
returns the following:

    Program received signal SIGSEGV: Segmentation fault - invalid memory
reference.

    Backtrace for this error: 
    #0  0x10b7310bc
    #1  0x10b7308aa
    #2  0x7fffe6ebdb39
    Segmentation fault: 11

when compiled with gfortran 7.1.1 2017062 on OSX from macports using the
following fortran flags:

    -g -fcheck=all -fbacktrace -fbounds-check -O0 -Wall -Wextra
-fno-strict-aliasing -fwrapv

The code also fails on linux with GNU Fortran (Ubuntu 7.1.0-5ubuntu2~14.04)
7.1.0 using the following fortran flags

    -O2 -fbacktrace -ffpe-summary=overflow -ffpe-trap=overflow,zero,invalid

The code runs successfully when compiled on ubuntu linux with the following:

    4.9.4
    5.4.1 20160904
    6.3.0 20170519

The segmentation fault occurs after the program completes allocation and
initialization of this%element(i)%obj on line 117 for each element and makes
the call to a_rd on line 121.

A segmentation fault does not occur if this%elements is defined as:

    type(Btype), pointer, dimensions(:) :: elements => null()

and the code is modified to reflect the change to this%elements.

Is this a bug in 7.1.1?