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To: fortran@gcc.gnu.org
From: Patrick Begou <Patrick.Begou@univ-grenoble-alpes.fr>
Subject: gfortran 10.2 and tests in debug mode
Message-ID: <3961ac8d-17d1-8391-25e0-a54ee51f4089@univ-grenoble-alpes.fr>
Date: Sat, 6 Feb 2021 17:59:01 +0100
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Hi,

this is my first post on this list.

I have a strange behavior with gfortran 10.2 freshly deployed.  This
small test-case program below give a segfault in debug mode only with
gfortran 10.2 and not with 7.3, 6.3.0 or 4.8.5.

In the real life, the do_it could be a parameter received in a function
saying "if 0 do nothing else do something every do_it timestep".

In my mind, if the first condition in the if line is false, the second
one must not be evaluated. But with gfortran 10.2 it is.

    program badtest
       implicit none
       integer:: i,do_it=0

       do i=1,4
          if (do_it > 0 .and. mod(i,do_it) .eq.0) then
             print*, "Do it!"
          else
             print*, "No!"
          endif
       enddo
    end program badtest


Compilation with:

*gfortran -O0 -Wall -g  -ffree-line-length-none -fbacktrace
-ffpe-trap=zero,overflow -finit-real=nan -fcheck=all badtest.F90 -o badtest*

I've split all such tests in 2 consecutives "if" lines in my code to
allow debuging but not sure it is the right behavior in Fortran.

Patrick