Using Optimization flag in Fortran

Using Optimization flag in Fortran

[Vardhan, Sundara (GE Infra, Energy)]

Hi All

Recently I added the -O3 flag to compile gfortran code. The application
uses OPEN() call to open files. These calls are made in a sequence, one
after another to open about 4 files before any operation on any of these
files are performed. This code works fine when compiled with no
Optimization flags. However upon adding the Optimization flags (be it -O
or -O3), the first OPEN() works fine and the next OPEN() call fails. I
suspect that the optimization flag turns on some check which may be
causing this failure. I would very much appreciate your help and advice
on what may be the reason for such a behaviour.

Thanks in advance

With Regards

Vardhan

Re: Using Optimization flag in Fortran

[Tim Prince]

Vardhan, Sundara (GE Infra, Energy) wrote:

> Recently I added the -O3 flag to compile gfortran code. The application
> uses OPEN() call to open files. These calls are made in a sequence, one
> after another to open about 4 files before any operation on any of these
> files are performed. This code works fine when compiled with no
> Optimization flags. However upon adding the Optimization flags (be it -O
> or -O3), the first OPEN() works fine and the next OPEN() call fails. I
> suspect that the optimization flag turns on some check which may be
> causing this failure. 
It looks more likely you have a bug in your program whose ill effect is 
worsened with optimization.  Perhaps you could find it by setting -O 
along with -Wall and subscript range checking.
It may also be useful to assure that you have a more stable version of 
gfortran than would be furnished by some of the "enterprise" linux distros.

RE: Using Optimization flag in Fortran

[Vardhan, Sundara (GE Infra, Energy)]

Hi Tim

Thanks much for your reply. I will try this out as soon as I get a
system to work on. I am working on RedHat Linux enterprise version but a
very old gcc - version 4.1.2.

With Regards

Vardhan 

-----Original Message-----
From: Tim Prince [mailto:n8tm@aol.com] 
Sent: Tuesday, December 01, 2009 8:53 AM
To: Vardhan, Sundara (GE Infra, Energy)
Cc: gcc-help@gcc.gnu.org
Subject: Re: Using Optimization flag in Fortran

Vardhan, Sundara (GE Infra, Energy) wrote:

> Recently I added the -O3 flag to compile gfortran code. The 
> application uses OPEN() call to open files. These calls are made in a 
> sequence, one after another to open about 4 files before any operation

> on any of these files are performed. This code works fine when 
> compiled with no Optimization flags. However upon adding the 
> Optimization flags (be it -O or -O3), the first OPEN() works fine and 
> the next OPEN() call fails. I suspect that the optimization flag turns

> on some check which may be causing this failure.
It looks more likely you have a bug in your program whose ill effect is
worsened with optimization.  Perhaps you could find it by setting -O
along with -Wall and subscript range checking.
It may also be useful to assure that you have a more stable version of
gfortran than would be furnished by some of the "enterprise" linux
distros.