[Bug fortran/60543] New: Random number problems with REAL64 precision at different optimization levels

[Bug fortran/60543] New: Random number problems with REAL64 precision at different optimization levels

[sarantis.pantazis at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

            Bug ID: 60543
           Summary: Random number problems with REAL64 precision at
                    different optimization levels
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sarantis.pantazis at gmail dot com

Created attachment 32365
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32365&action=edit
code and compiled files

The attached code is meant to generate particle velocities with different
magnitudes but uniform angle distribution. In this process, I have checked the
sign of the three velocity components and have found the following:

(1) In DEBUG mode (-O0, please see the included makefile for the exact flags)
no problem appears.
(2) In OPT1 mode (-O1) the number of positive components in the y- and z-
direction seem to be always the same.
(3) In OPT1 mode the code "gets stuck" if I deactivate the WRITE statements of
lines 31 and 34 in bugMain.f.

No error/warning messages given by the compiler.

I have attached a compiled version of (1)-(3) with the -save-temps flag.


The output of lsb_release -a:

LSB Version:   
core-2.0-amd64:core-2.0-noarch:core-3.0-amd64:core-3.0-noarch:core-3.1-amd64:core-3.1-noarch:core-3.2-amd64:core-3.2-noarch:core-4.0-amd64:core-4.0-noarch:core-4.1-amd64:core-4.1-noarch:security-4.0-amd64:security-4.0-noarch:security-4.1-amd64:security-4.1-noarch
Distributor ID:    Ubuntu
Description:    Ubuntu 13.10
Release:    13.10
Codename:    saucy


The output of gfortran -v:

Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.8.1-10ubuntu9' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.8 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin
--with-system-zlib --disable-browser-plugin --enable-java-awt=gtk
--enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu9)

[Bug fortran/60543] [4.8/4.9 Regression] Function with side effect removed by the optimizer.

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-03-16
            Summary|Random number problems with |[4.8/4.9 Regression]
                   |REAL64 precision at         |Function with side effect
                   |different optimization      |removed by the optimizer.
                   |levels                      |
     Ever confirmed|0                           |1

--- Comment #1 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Confirmed, although this has nothing to do with REAL64 precision nor with
random number. The problem comes from the fact that one call to random() is
optimized away.

On trunk (4.9) the code is optimized as with following changes:

@@ -45,7 +45,7 @@ USE globalParameters
 USE generalFunctions
 IMPLICIT NONE

-REAL(DP):: magnitude
+REAL(DP):: magnitude, tmp
 REAL(DP):: mass
 REAL(DP):: angle1, angle2
 REAL(DP):: upsilon0_local, gasConstant, T
@@ -71,11 +71,12 @@ DO i=1,2000
     DO
         magnitude = 5e0_DP*random()
 !        WRITE(*,*) magnitude, EXP(-magnitude**2)
-        IF ( random() <= EXP(-magnitude**2) ) EXIT
+        tmp = random()
+        IF ( tmp <= EXP(-magnitude**2) ) EXIT
     END DO
 !    WRITE(*,*)

-    angle1=random()*twopi
+    angle1=tmp*twopi
     angle2=ACOS(2e0_DP*random()-1e0_DP) ; angle2=angle2-pi/2e0_DP

     upsilon0_local=SQRT(2e0_DP * gasConstant * T)

For the moment I don't really understand what is happening with 4.8, i.e.,
infinite loop. AFAIU the dumps it looks optimized as

@@ -69,9 +69,10 @@ T=293.15e0_DP
 DO i=1,2000

     DO
-        magnitude = 5e0_DP*random()
+        tmp = random()
+        magnitude = 5e0_DP*tmp
 !        WRITE(*,*) magnitude, EXP(-magnitude**2)
-        IF ( random() <= EXP(-magnitude**2) ) EXIT
+        IF ( tmp <= EXP(-magnitude**2) ) EXIT
     END DO
 !    WRITE(*,*)

But the executable does not hang when compiled with 4.7.4 or trunk.

[Bug fortran/60543] [4.8/4.9 Regression] Function with side effect removed by the optimizer.

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
                 CC|                            |burnus at gcc dot gnu.org
   Target Milestone|---                         |4.8.3

--- Comment #2 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Confirmed.

The problem is that "function random" is regarded as (implicit) pure. However,
gfortran's subroutine random_number is properly declared as impure.

Reduced example:

  module m
  contains
    REAL(8) FUNCTION random()
      CALL RANDOM_NUMBER(random)
    END FUNCTION random
  end module m

$ zgrep -i pure m.mod 
0 0 FUNCTION IMPLICIT_PURE) () (REAL 8 0 0 0 REAL ()) 0 0 () () 3 () ()

Draft patch:

--- a/gcc/fortran/intrinsic.c
+++ b/gcc/fortran/intrinsic.c
@@ -4407 +4407 @@ gfc_intrinsic_sub_interface (gfc_code *c, int error_flag)
-  if (gfc_pure (NULL) && !isym->pure)
+  if (!isym->pure && gfc_pure (NULL))
@@ -4413,0 +4414,3 @@ gfc_intrinsic_sub_interface (gfc_code *c, int error_flag)
+  if (!isym->pure && gfc_implicit_pure (NULL))
+    gfc_current_ns->proc_name->attr.implicit_pure = 0;
+

[Bug fortran/60543] [4.8/4.9 Regression] Function with side effect removed by the optimizer.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4
                 CC|                            |jakub at gcc dot gnu.org

[Bug fortran/60543] [4.8/4.9 Regression] Function with side effect removed by the optimizer.

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Author: burnus
Date: Wed Mar 19 21:03:14 2014
New Revision: 208687

URL: http://gcc.gnu.org/viewcvs?rev=208687&root=gcc&view=rev
Log:
2014-03-18  Tobias Burnus  <burnus@net-b.de>

        PR fortran/60543
        PR fortran/60283
        * gfortran.h (gfc_unset_implicit_pure): New prototype.
        * resolve.c (gfc_unset_implicit_pure): New.
        (resolve_structure_cons, resolve_function,
        pure_subroutine): Use it.
        * decl.c (match_old_style_init, gfc_match_data,
        match_pointer_init, variable_decl): Ditto.
        * expr.c (gfc_check_pointer_assign): Ditto.
        * intrinsic.c (gfc_intrinsic_sub_interface): Ditto.
        * io.c (match_vtag, gfc_match_open, gfc_match_close,
        match_filepos, gfc_match_inquire, gfc_match_print,
        gfc_match_wait): Ditto.
        * match.c (gfc_match_critical, gfc_match_stopcode,
        lock_unlock_statement, sync_statement, gfc_match_allocate,
        gfc_match_deallocate): Ditto.
        * parse.c (decode_omp_directive): Ditto.
        * symbol.c (gfc_add_save): Ditto.

2014-03-18  Tobias Burnus  <burnus@net-b.de>

        PR fortran/60543
        PR fortran/60283
        * gfortran.dg/implicit_pure_4.f90: New.


Added:
    trunk/gcc/testsuite/gfortran.dg/implicit_pure_4.f90
Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/decl.c
    trunk/gcc/fortran/expr.c
    trunk/gcc/fortran/gfortran.h
    trunk/gcc/fortran/intrinsic.c
    trunk/gcc/fortran/io.c
    trunk/gcc/fortran/match.c
    trunk/gcc/fortran/parse.c
    trunk/gcc/fortran/resolve.c
    trunk/gcc/fortran/symbol.c
    trunk/gcc/testsuite/ChangeLog

[Bug fortran/60543] [4.8/4.9 Regression] Function with side effect removed by the optimizer.

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #4 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Author: burnus
Date: Thu Mar 20 06:53:01 2014
New Revision: 208693

URL: http://gcc.gnu.org/viewcvs?rev=208693&root=gcc&view=rev
Log:
2014-03-19  Tobias Burnus  <burnus@net-b.>

        PR fortran/60543
        * io.c (check_io_constraints): Use gfc_unset_implicit_pure.
        * resolve.c (resolve_ordinary_assign): Ditto.


Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/io.c
    trunk/gcc/fortran/resolve.c

[Bug fortran/60543] [4.8/4.9 Regression] Function with side effect removed by the optimizer.

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #6 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Author: burnus
Date: Thu Mar 20 19:42:15 2014
New Revision: 208733

URL: http://gcc.gnu.org/viewcvs?rev=208733&root=gcc&view=rev
Log:
2014-03-20  Tobias Burnus  <burnus@net-b.de>

        PR fortran/60543
        PR fortran/60283
        * gfortran.h (gfc_unset_implicit_pure): New prototype.
        * resolve.c (gfc_unset_implicit_pure): New.
        (resolve_structure_cons, resolve_function,
        pure_subroutine, resolve_ordinary_assign): Use it.
        * decl.c (match_old_style_init, gfc_match_data,
        match_pointer_init, variable_decl): Ditto.
        * expr.c (gfc_check_pointer_assign): Ditto.
        * intrinsic.c (gfc_intrinsic_sub_interface): Ditto.
        * io.c (match_vtag, gfc_match_open, gfc_match_close,
        match_filepos, gfc_match_inquire, gfc_match_print,
        gfc_match_wait, check_io_constraints): Ditto.
        * match.c (gfc_match_critical, gfc_match_stopcode,
        lock_unlock_statement, sync_statement, gfc_match_allocate,
        gfc_match_deallocate): Ditto.
        * parse.c (decode_omp_directive): Ditto.
        * symbol.c (gfc_add_save): Ditto.

2014-03-20  Tobias Burnus  <burnus@net-b.de>

        PR fortran/60543
        PR fortran/60283
        * gfortran.dg/implicit_pure_4.f90: New.


Added:
    branches/gcc-4_7-branch/gcc/testsuite/gfortran.dg/implicit_pure_4.f90
Modified:
    branches/gcc-4_7-branch/gcc/fortran/ChangeLog
    branches/gcc-4_7-branch/gcc/fortran/decl.c
    branches/gcc-4_7-branch/gcc/fortran/gfortran.h
    branches/gcc-4_7-branch/gcc/fortran/intrinsic.c
    branches/gcc-4_7-branch/gcc/fortran/io.c
    branches/gcc-4_7-branch/gcc/fortran/match.c
    branches/gcc-4_7-branch/gcc/fortran/parse.c
    branches/gcc-4_7-branch/gcc/fortran/resolve.c
    branches/gcc-4_7-branch/gcc/fortran/symbol.c
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog

[Bug fortran/60543] [4.8/4.9 Regression] Function with side effect removed by the optimizer.

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #5 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Author: burnus
Date: Thu Mar 20 19:42:00 2014
New Revision: 208732

URL: http://gcc.gnu.org/viewcvs?rev=208732&root=gcc&view=rev
Log:
2014-03-20  Tobias Burnus  <burnus@net-b.de>

        PR fortran/60543
        PR fortran/60283
        * gfortran.h (gfc_unset_implicit_pure): New prototype.
        * resolve.c (gfc_unset_implicit_pure): New.
        (resolve_structure_cons, resolve_function,
        pure_subroutine, resolve_ordinary_assign): Use it.
        * decl.c (match_old_style_init, gfc_match_data,
        match_pointer_init, variable_decl): Ditto.
        * expr.c (gfc_check_pointer_assign): Ditto.
        * intrinsic.c (gfc_intrinsic_sub_interface): Ditto.
        * io.c (match_vtag, gfc_match_open, gfc_match_close,
        match_filepos, gfc_match_inquire, gfc_match_print,
        gfc_match_wait, check_io_constraints): Ditto.
        * match.c (gfc_match_critical, gfc_match_stopcode,
        lock_unlock_statement, sync_statement, gfc_match_allocate,
        gfc_match_deallocate): Ditto.
        * parse.c (decode_omp_directive): Ditto.
        * symbol.c (gfc_add_save): Ditto.

2014-03-20  Tobias Burnus  <burnus@net-b.de>

        PR fortran/60543
        PR fortran/60283
        * gfortran.dg/implicit_pure_4.f90: New.


Added:
    branches/gcc-4_8-branch/gcc/testsuite/gfortran.dg/implicit_pure_4.f90
Modified:
    branches/gcc-4_8-branch/gcc/fortran/ChangeLog
    branches/gcc-4_8-branch/gcc/fortran/decl.c
    branches/gcc-4_8-branch/gcc/fortran/expr.c
    branches/gcc-4_8-branch/gcc/fortran/gfortran.h
    branches/gcc-4_8-branch/gcc/fortran/intrinsic.c
    branches/gcc-4_8-branch/gcc/fortran/io.c
    branches/gcc-4_8-branch/gcc/fortran/match.c
    branches/gcc-4_8-branch/gcc/fortran/parse.c
    branches/gcc-4_8-branch/gcc/fortran/resolve.c
    branches/gcc-4_8-branch/gcc/fortran/symbol.c
    branches/gcc-4_8-branch/gcc/testsuite/ChangeLog

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|4.8.3                       |4.7.4
            Summary|[4.8/4.9 Regression]        |[4.7/4.8/4.9 Regression]
                   |Function with side effect   |Function with side effect
                   |removed by the optimizer.   |removed by the optimizer.

--- Comment #7 from Tobias Burnus <burnus at gcc dot gnu.org> ---
FIXED on the 4.7 and 4.8 branches and on the trunk (to become 4.9.0).

Thanks for the report and sorry for the breakage!

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[sarantis.pantazis at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #8 from Sarantis Pantazis <sarantis.pantazis at gmail dot com> ---
Created attachment 32430
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32430&action=edit
Compilation logs and installation workflow

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[sarantis.pantazis at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #9 from Sarantis Pantazis <sarantis.pantazis at gmail dot com> ---
Thank you for the fast response and effort. I have installed gcc from svn but
the results are still the same. Perhaps I mis-installed something? Attached you
will find the logs and the installation workflow. Is step #14 perhaps wrong?

The output of gfortran -v seems correct though.

Using built-in specs.
COLLECT_GCC=/home/sarantis/latestGcc/gcc-build/gcc/gfortran
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --prefix=/home/sarantis/latestGcc
--enable-languages=c,fortran,c++ --disable-multilib
Thread model: posix
gcc version 4.9.0 20140323 (experimental) (GCC)

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #10 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> Thank you for the fast response and effort. I have installed gcc from svn
> but the results are still the same. Perhaps I mis-installed something?
> Attached you will find the logs and the installation workflow.
> Is step #14 perhaps wrong?

Did you recompile the module defining random()?

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #12 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> Yes, I did; I used "make clean" first (also "rm *.o *.f90 *.s" in the main
> folder to clean up the files generated by -save-temps).

Did you update the compiler name in your makefile? I have just been caught by
that when comparing the results in the bug_OPT1mode_withWRITE and
bug_OPT1mode_noWRITE directories. With the right compiler for both, I get

        2000        1058        1005        1017

Can you do the following

cp MOD/generalfunctions.mod generalFunctions.mod.gz
gunzip generalFunctions.mod.gz
grep PURE generalFunctions.mod

you should only see

UNKNOWN-PROC DECL UNKNOWN 0 0 INTRINSIC FUNCTION PURE) () (CHARACTER 1 0
UNKNOWN-PROC DECL UNKNOWN 0 0 INTRINSIC FUNCTION PURE) () (CHARACTER 1 0

i.e., no IMPLICIT_PURE.

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[sarantis.pantazis at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #13 from Sarantis Pantazis <sarantis.pantazis at gmail dot com> ---
> Did you update the compiler name in your makefile?

I have left the line COMPILER=gfortran at the top as it is and I have defined
an alias in my ~/.bashrc for gfortran pointing to the newly installed location
(alias gfortran='$HOME/latestGcc/gcc-build/gcc/gfortran').


> cp MOD/generalfunctions.mod generalFunctions.mod.gz
> gunzip generalFunctions.mod.gz

I get "gzip: generalFunctions.mod.gz: not in gzip format". But anyway, the mod
file is readable so I can skip to the third line.


> grep PURE generalFunctions.mod

UNKNOWN-INTENT MODULE-PROC DECL UNKNOWN 0 0 SUBROUTINE IMPLICIT_PURE) (
MODULE-PROC DECL UNKNOWN 0 0 FUNCTION IMPLICIT_PURE) (REAL 8 0 0 0 REAL

So, I still get IMPLICIT_PURE. And when I run it I still get the infinite loop
as well, so I guess I missed something during the installation?

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[mikael at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

Mikael Morin <mikael at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mikael at gcc dot gnu.org

--- Comment #14 from Mikael Morin <mikael at gcc dot gnu.org> ---
(In reply to Sarantis Pantazis from comment #13)
> > Did you update the compiler name in your makefile?
> 
> I have left the line COMPILER=gfortran at the top as it is and I have
> defined an alias in my ~/.bashrc for gfortran pointing to the newly
> installed location (alias gfortran='$HOME/latestGcc/gcc-build/gcc/gfortran').
> 
> 
> > cp MOD/generalfunctions.mod generalFunctions.mod.gz
> > gunzip generalFunctions.mod.gz
> 
> I get "gzip: generalFunctions.mod.gz: not in gzip format". But anyway, the
> mod file is readable so I can skip to the third line.
> 
This means you are using an old compiler.
Did you install the compiler (i.e. run 'make install')?
Do you get gzip'ed modules if you use .../gcc/f951 instead of .../gcc/gfortran?

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[sarantis.pantazis at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #15 from Sarantis Pantazis <sarantis.pantazis at gmail dot com> ---
> Did you install the compiler (i.e. run 'make install')?

Yes, I did. I read http://gcc.gnu.org/install/index.html and made a summary of
the steps I followed (attached here). I also kept a log of "make" and "make
install" (also attached here).


I also tried changing COMPILER=gfortran to
COMPILER=/home/sarantis/latestGcc/gcc-build/gcc/gfortran and got the following
error:

gfortran: error trying to exec 'f951': execvp: No such file or directory


> Do you get gzip'ed modules if you use .../gcc/f951 instead of .../gcc/gfortran?

Compiling with COMPILER=/home/sarantis/latestGcc/gcc-build/gcc/f951 leads to
zipped files and no IMPLICIT_PURE. But f951 does not accept -c so no executable
was produced.


It seems it is something trivial but my knowledge outside of fortran is still
rather limited...

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[anlauf at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #16 from Harald Anlauf <anlauf at gmx dot de> ---
(In reply to Sarantis Pantazis from comment #13)
> > Did you update the compiler name in your makefile?
> 
> I have left the line COMPILER=gfortran at the top as it is and I have
> defined an alias in my ~/.bashrc for gfortran pointing to the newly
> installed location (alias gfortran='$HOME/latestGcc/gcc-build/gcc/gfortran').

I think that aliases in a Makefile are a bad idea.  You need to make sure
that the aliases are exported from the invoking shell.

On my system I get:

% alias gfc
alias gfc='gfortran'
% cat Makefile

SHELL = /bin/bash

aliastest:
        echo "Running make: alias:"; alias
% make aliastest
echo "Running make: alias:"; alias
Running make: alias:

So no aliases are set!  Try "man bash" and search for "expand_aliases".
I use a symbolic link gfc-trunk (you might prefer gfortran-latest)
to the installed binary and use this in the makefile.

[Bug fortran/60543] [4.7/4.8/4.9 Regression] Function with side effect removed by the optimizer.

[kargl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543

--- Comment #17 from kargl at gcc dot gnu.org ---
(In reply to Sarantis Pantazis from comment #15)
>
> It seems it is something trivial but my knowledge outside of fortran is
> still rather limited...
>

Bugzilla is not a Fortran User support forum.  But, to aid in your
suffering.  Remove ALL installed versions of gfortran.  Make sure
that there are no leftover gfortrans or f951 in your path and remove
all old *.mod files.  Now, re-install the latest and greatest version
of gfortran from trunk.