[Bug fortran/96018] New: Optimization issue with external HDF5 library

[martin.schlipf at damnthespam dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96018

            Bug ID: 96018
           Summary: Optimization issue with external HDF5 library
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: martin.schlipf at damnthespam dot com
  Target Milestone: ---

Created attachment 48817
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48817&action=edit
Minimal example to demonstrate the issue.

On a clean Ubuntu 20.04 with the following setup

sudo apt-get update
sudo apt-get install gfortran-10
sudo apt-get install libhdf5-dev

the attached code produces an error when compiled with optimization

gfortran-10 -O2 hdf5_bug.f90 -I/usr/include/hdf5/serial/
-L/usr/lib/x86_64-linux-gnu/ -lhdf5_serial_fortran

As far as I can tell, the reason this appears is that the compiler fails to
recognize that the function call in line 98 has side effects and optimizes it
away. If you check the status of the error code, the issue disappears.
Strangely, the exact same sequence of calls with a 2d array instead of a 3d one
works fine.