[Bug libfortran/41335] VOLATILE in Fortran does not take effect

[sgk at troutmask dot apl dot washington dot edu]

------- Comment #13 from sgk at troutmask dot apl dot washington dot edu  2009-09-11 20:26 -------
Subject: Re:  VOLATILE in Fortran does not take effect

> 
> What is your hardware? x86 or something else?

Opteron.

> I have Atlon 2000 MP and Intel Quad and on both of these systems I get
> differences in output for "real" and "double precision".
> 
> What I can do to prove that I do have differences and what to do to find out
> why?
> 

Have you tried -ffloat-store?  This should save/load a FPU register
after every operation. 

There is the -fpmath= option, but I'm not sure which switches
are appropriate for your cpu.  There is also the -msse set of
options.

To find out why you have differences, print out intermediate values
to 16 and 7 significant figures for real and double precision.  It
may also be helpful to read Goldberg's paper if you haven't (see
the gfortran wiki, manuals section).


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41335